# Sustainable Amination of Bio-Based Alcohols by Hydrogen Borrowing Catalysis

Sophie Hameury, H. Bensalem, Karine de Oliveira Vigier

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Sophie Hameury, H. Bensalem, Karine de Oliveira Vigier. Sustainable Amination of Bio-Based Alcohols by Hydrogen Borrowing Catalysis. Catalysts, 2022, 12 (11), pp.1306. 10.3390/catal12111306. hal-04233934

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Review

# Sustainable Amination of Bio-Based Alcohols by Hydrogen Borrowing Catalysis

Sophie Hameury* ID, Hana Bensalem and Karine De Oliveira Vigier ID

Institut de Chimie des Milieux et Matériaux de Poitiers (IC2MP), Université de Poitiers, CNRS, F-86073 Poitiers, France

* Correspondence: sophie.hameury@univ-poitiers.fr

**Abstract:** In this review, we aim to give an overview of the use of the Borrowing Hydrogen (BH) methodology with bio-based alcohols. This methodology only forms water as a by-product, thus providing a sustainable way to amines, which have a large range of applications. This process is of particular interest when related to biomass due to the high abundance of alcohol functions in natural compounds. However, natural compounds often comprise multiple chemical functions that can change the reactivity of the substrate. This comprehensive review, comprising both homogeneous and heterogeneous catalysts, aims at summarizing the recent advancements in biomass amination for every class of substrate, highlighting the key parameters governing their reactivity and the remaining scientific hurdles. Even though most substrates have successfully been converted into the corresponding amines, reaction selectivity and functional group tolerance still need to be improved.

**Keywords:** bio-based alcohol; amination; hydrogen borrowing

<figure><img src="image_2.png" /></figure>

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**Citation:** Hameury, S.; Bensalem, H.; De Oliveira Vigier, K. Sustainable Amination of Bio-Based Alcohols by Hydrogen Borrowing Catalysis.

*Catalysts* **2022**, *12*, 1306. https://doi.org/10.3390/catal12111306

Academic Editors: Nicolas Abatzoglou and Ajay K. Dalai

Received: 15 September 2022

Accepted: 16 October 2022

Published: 24 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

## 1. Introduction

Replacing fossil fuels used in the production of energy or as industrial feedstocks with renewable sources has become the paramount objective in combating climate change and environmental pollution. In this context, biorefining, which aims to use biomass as a raw material, stands out as a relevant solution towards sustainable development [1]. Because of the inherent differences between hydrocarbons—simple molecules composed of C and H atoms—and the complex entities that make up biomass feedstocks, new approaches are required to achieve efficient conversion. Lignocellulosic biomass represents 90% of all plants and presents the advantage of being abundant and available from non-edible resources. Lignocellulose is composed of lignin, cellulose, and hemicellulose and is easily available from waste residue. Cellulose and hemicellulose are carbohydrate polymers and thus contain large amounts of oxygen atoms, often in the form of hydroxyl functions, which are also found in a large number of natural compounds [2]. Hydroxyl groups have two reactive bonds: the C-O and the O-H bonds, each of which displays a particular reactivity. Aside from the well-known redox and elimination reactions, substitution pathways are a possibility, and mastering them could pave the way to a large variety of compounds. On the one hand, substitution of the hydroxyl hydrogen proved to be relatively easy due to its acid nature. On the other hand, nucleophilic substitution of the hydroxyl moiety can be problematic due to the poor leaving group ability of the OH group. To circumvent its low reactivity, acids can be added, but the main drawback of this strategy lies in the stoichiometric amounts often required along with the formation of side products. Transforming the alcohol functional groups into more reactive entities via treatment with SOCl₂ or PBr₃ is another possible approach with the inconvenience of adding an extra step to the synthesis.

A particular interest is devoted to the formation of amines as they are essential building blocks used to yield pharmaceutical compounds, solvents, food additives, polymer
materials, personal care products, detergents, or agrochemicals. On a general basis, amines can be obtained by various methods such as the Hofmann N-alkylation reaction, the Gabriel method, reduction of nitro compounds, Ullmann/Buchwald-Hartwig coupling, reductive amination, and hydroamination [3]. These approaches involve multiple steps and/or generate a stoichiometric amount of waste. Alternatives are thus in high demand.

The conversion of oxygen-rich biomass into amines usually involves C=O bond transformations since they are easily reactive and can undergo reductive amination reactions [4]. However, when these bonds are not present in the initial substrate, an extra step involving a stoichiometric amount of oxidant must be added to form the C=O moiety. Alternatively, the borrowing hydrogen methodology (BH) can be used when alcohol functions are found in the substrate. This reaction is also referred to as transfer hydrogenation or hydrogen autotransfer (Scheme 1) [5–7].

<figure><img src="image_4.png" /><figcaption>**Scheme 1.** Alcohol amination via hydrogen borrowing.</figcaption></figure>

Complex structures can be catalytically obtained in only one step, thus suppressing multistep sequences. The key step of this methodology involves dehydrogenation of the substrate and its storage on the catalyst for later use in the last step of the catalytic cycle. Within only one step, oxidation/dehydrogenation and reduction/hydrogenation reactions are coupled, thus allowing the coupling of exothermic with endothermic reactions, which presents various advantages [8]. When this methodology is applied to an alcohol, the transformation starts with the dehydrogenation of the alcohol, forming a carbonyl moiety in concomitance with the catalyst hydrogenation. This step is followed by the classical amine/carbonyl condensation to form the corresponding imine. Finally, hydrogenation of the imine occurs, leading to the targeted amine such as the regeneration of the catalyst to complete the catalytic cycle. The H₂ used for this transformation arises from the catalyst (from the first dehydrogenation). The need for a stoichiometric amount of oxidant/reductant is thus removed. It is important to note that in some cases, extra H₂ was required to perform the reaction. An imbalance between the hydrogen borrowed from the substrate and consumed during the reaction can thus be observed. This extra hydrogen can be needed to prevent the catalyst deactivation, to reduce the amount of catalyst used, to control the selectivity of the reaction or to help to perform the last hydrogenation step [9].

Alcohol amination was first mentioned in 1932 by Winans and Adkins [10]. Hydrogen borrowing using homogeneous catalysts was first reported by Grigg [11] and Watanabe [12] and is gaining increasing attention due to the ease of the synthesis and the low amount of by-products formed. The term "borrowing hydrogen" was first used in 2004 [13] and was followed by extensive research on the topic. This has become an appealing methodology since functionalization of a large variety of alcohols is possible, with water being the only by-product formed in contrast with classical amine synthesis methods.
Due to the high presence of alcohol functions in natural substrates, this methodology was applied to a large variety of compounds arising from biomass, such as terpenes, furan derivatives, isohexides, fatty alcohols, diols, triols, polyfunctional alcohols, and carbohydrates (Scheme 2). Herein, we review these reactions and identify the key parameters for the amination of natural substrates. As an example, the use of fatty alcohols involves the presence of long aliphatic chains. The impact of these chains on the reaction conditions will be examined. The presence of multiple chemical functions will also be evaluated (double bonds, heterocycles, amides, carboxylic acids, and esters). Finally, the impact of the presence of multiple alcohol functions will be investigated. A large alcohol structural diversity can indeed be produced from biomass, and each class of natural substances will present some particular specificities. We have decided to classify the substrates used, to give a general trend for the BH amination. The latest studies on biomass amination via BH methodology will be summarized and discussed in this comprehensive review with an emphasis on the structure/functionalization-reactivity relationship.

<figure><img src="image_5.png" /><figcaption>**Scheme 2.** Substrate aminated with a borrowing hydrogen strategy.</figcaption></figure>

## 2. Amination of Bio-Based Alcohols by Hydrogen Borrowing Catalysis

### 2.1. Fatty Alcohols

Fatty alcohols are derived from natural fats and oils and correspond to long-straight-chain primary alcohols. The amination of small-chain alcohols has been extensively studied and is well documented in the literature [5,6]. We will only discuss long-chain fatty alcohols with carbon chains containing at least 14 carbon atoms. To the best of our knowledge, only two examples are reported in the literature [14]. The fatty alcohols were aminated in methoxycyclopentane using [Ni(cod)₂] as catalyst, in the presence of 30 mol% of KOH with an 85–90% yield (Scheme 3). KOH is used to stabilize the in situ formed Ni nanoparticles. This methodology is well suited for the amination of alcohols with aniline, but the use
of aliphatic amines, leads to catalyst poisoning due to the increased basicity of aliphatic amines thus providing a stronger coordination ability. Shorter aliphatic chains could also be aminated and give similar yields. The length of the aliphatic chain has no impact on the reactivity of the catalytic system. In 2021, Ding et al. reported a homogeneous catalyst that was efficient in the presence of a base as an additive with slightly increased yields (90–99%) [15].

<figure><img src="image_6.png" /><figcaption>**Scheme 3.** Amination of fatty alcohols.</figcaption></figure>

## 2.2. Terpenoids

Terpenoids are natural compounds arising from isoprene units that can be found in plants and are often used for their aromatic properties. They present a large structural and functional variety, and some display alcohol functions that were used in hydrogen borrowing reactions.

Vogt et al. described in 2013 the amination of various alcohols belonging to the terpene family (Scheme 4) [16]. Satisfactory conversion ranging from 32 to 99% was achieved depending on the substrate used. Selectivity varied from 44 to 98% due to the high functionality of the targeted terpenoids. As an example, since unsaturations are commonly found in terpenoids, the intermediate formation of enals is observed. They could easily isomerize to a mixture of compounds (such as the corresponding saturated amines or alcohols). Additionally, the formation of secondary amines from the primary alcohols was also observed, i.e., the dialkylation of ammonia instead of the desired monoalkylation. Moreover, in the case of bulky terpenoids, the reaction is hardly completed. The corresponding ketone is thus the main product obtained with these substrates. This highlights some of the difficulties encountered with natural substrates.

<figure><img src="image_7.png" /><figcaption>**Scheme 4.** Terpene amination.</figcaption></figure>

## 2.3. Furan Derivatives

Furan derivatives can be obtained via the dehydration of carbohydrate monomers under acid conditions. The amination of several furan derivatives is reported in the literature: mainly 5-(hydroxymethyl)furfural (5-HMF), 2,5-bis(hydroxymethyl)furan (BHMF), and furfuryl alcohol. In addition, rare examples of 1-(2-furyl)ethanol, 5-methylfurfuryl alcohol or tetrahydrofurfuryl alcohol were also mentioned in the literature. This section will be ordered according to the alcohol substrate used.
### 2.3.1. Furfuryl Alcohol

Furfuryl alcohol was aminated under various reaction conditions. Interestingly, a large structural variety of products was obtained, such as various primary, secondary, or tertiary amines, depending on the amine substrates and the reaction conditions (Scheme 5).

<figure><img src="image_8.png" /><figcaption>**Scheme 5.** Furfuryl alcohol amination.</figcaption></figure>

#### Ammonia as a Nitrogen Source

Only two different structures are accessible from furfuryl alcohol and ammonia: furfuryl amine and its hydrogenated counterpart, tetrahydrofurfurylamine (Scheme 6).

<figure><img src="image_9.png" /><figcaption>**Scheme 6.** Furfuryl alcohol amination using ammonia as a nitrogen source.</figcaption></figure>

The catalytic systems used to provide furfuryl amine from furfuryl alcohol and ammonia are summarized in Table 1.

<table><caption>**Table 1.** Catalytic synthesis of furfuryl amine.</caption><thead><tr><th>Entry</th><th>Catalyst</th><th>T (°C)</th><th>t (h)</th><th>Solvent</th><th>Additive</th><th>Yield (%)</th><th>Ref</th></tr></thead><tbody><tr><td>1</td><td>Ru-PNP complex<br/>[Ru<sub>3</sub>CO<sub>12</sub>]/</td><td>135</td><td>12</td><td>Toluene</td><td>—</td><td>95</td><td>[17]</td></tr><tr><td>2</td><td>CataCXium® PCy</td><td>150</td><td>20</td><td>Neat</td><td>—</td><td>71</td><td>[18]</td></tr><tr><td>3</td><td>Ru nanoparticles</td><td>180</td><td>20</td><td>Neat</td><td>H<sub>2</sub> (2 bar)</td><td>38</td><td>[19]</td></tr><tr><td>4</td><td>Ru/Al<sub>2</sub>O<sub>3</sub></td><td>180</td><td>20</td><td>Neat</td><td>H<sub>2</sub> (2 bar)</td><td>10</td><td>[19]</td></tr><tr><td>5</td><td>Ru-MgO/TiO<sub>2</sub></td><td>110</td><td>20</td><td>Toluene</td><td>—</td><td>94</td><td>[20]</td></tr><tr><td>6</td><td>RANEY® Ni</td><td>180</td><td>24</td><td>THF</td><td>—</td><td>82</td><td>[21]</td></tr><tr><td>7</td><td>Ni/Al<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub></td><td>160</td><td>18</td><td>t-amyl<br/>alcohol</td><td>—</td><td>52</td><td>[22]</td></tr></tbody></table>
This reaction was first reported in 2008 by Milstein et al. with the synthesis and catalytic activity of an acridine-based Ru complex for the production of primary amines (Scheme 7, Table 1 Entry 1) [17]. This catalyst provided 95% of furfurylamine after 12 h. This particular catalyst is believed to operate via metal-ligand cooperation. Indeed, the acridine moiety is known to dearomatize and thus activate the alcohol in concomitance with the metallic center to perform the oxidation of the alcohol to a carbonyl [23]. In 2010, Beller also described the synthesis of the primary amine in 71% yield using [Ru₃CO₁₂]/CataCXium® PCy as a catalyst (Table 1 Entry 2) [18]. Even though a lower yield was obtained compared to the previous report by Milstein, the catalytic system is commercially available.

<figure><img src="image_10.png" /><figcaption>**Scheme 7.** Furfuryl alcohol amination to the corresponding primary amine.</figcaption></figure>

Additionally, for these homogeneous systems, several heterogeneous catalysts were reported (Table 1 Entry 3–7). To the best of our knowledge, only Ru- and Ni-based catalysts have been described. Although the non-supported Ru nanoparticles proved to have superior catalytic activity, the primary amine yield was quite low: 38 and 10% for Ru NP and Ru/Al₂O₃, respectively (Table 1 Entry 3 and 4) [19]. The yield of the reaction was drastically increased in 2020 with the work of Hara (Table 1 Entry 5) [20]. In the presence of Ru-MgO/TiO₂, 94% of the desired furfurylamine was obtained. The main advantage of this catalyst, besides its high yield, is that no external H₂ was needed for the reaction to proceed at excellent yields.

Earth abundant based catalysts were also efficient in furfuryl alcohol amination with ammonia. The most efficient system consists of the use of RANEY® Ni (Table 1, Entry 6) [21,24]. When this catalyst was used, furfuryl alcohol could be transformed into either furfurylamine or tetrahydrofurfurylamine depending on the reaction conditions (Scheme 8) [21,24]. Indeed, the selectivity of the reaction was driven by the presence of H₂. Although the alcohol amination does not require the use of external H₂ since it is "borrowed" from the alcohol dehydrogenation, it is mandatory for the hydrogenation of the furan ring. Indeed, 1 MPa of H₂ led to the hydrogenation of the furan ring in addition to the amination reaction, thus forming tetrahydrofurfurylamine. Whereas the catalyst could be reused at least five times in the case of the tetrahydrofurfurylamine, the absence of H₂ pressure for the furfurylamine formation catalysis led to catalyst deactivation after one run [21]. The remarkable catalytic activity of RANEY® Ni was ascribed to the small absorption energy difference between NH₃ and H₂. Thanks to this small difference, some of the active sites of the catalyst are available to perform the dehydrogenation/hydrogenation reactions that are required for the amination to occur and thus improve the overall catalytic activity of the catalyst [21].

<figure><img src="image_11.png" /><figcaption>**Scheme 8.** Furfuryl alcohol amination over RANEY® Ni.</figcaption></figure>
Primary Amines as a Nitrogen Source

Furfuryl amination using a primary amine as a nitrogen source led to the expected furfuryl amine and to more unexpected structures. Indeed, cyclic aminated compounds can be obtained from the use of diamine as a nitrogen source, and one example of amidation has been reported (Scheme 9).

<figure><img src="image_12.png" /><figcaption>**Scheme 9.** Furfuryl alcohol amination/amidation using a primary amine as a nitrogen source.</figcaption></figure>

If a primary amine was used instead of ammonia, secondary amines were obtained under various conditions. The catalytic activity of various homogeneous catalysts was assessed and resulted in yields ranging from 66 to 93% (Table 2 Entry 1–6). The first report in 2007 described the use of [Ru$_3$CO$_{12}$]/CataCXium® PCy, which allowed the isolation of 66% of products (Table 2 Entry 1) [25]. Only a moderate yield was obtained for this reaction due to the occurrence of side reactions (mainly difuryl side products). More and more well-defined catalysts were designed, synthesized, and investigated on natural alcohol, such as a complex containing a tridentate P,N,O ligand which efficiently catalyzed the amination of furfuryl alcohol with aniline with a 68% yield in only 4 h (Scheme 10, Table 2 Entry 2) [26]. It is worth mentioning that the presence of a base as an additive was used for this reaction. The base was assumed to deprotonate the alcohol, thus facilitating the coordination of the formed alcoholate to the Ru center.

<table><caption>**Table 2.** Catalytic furfuryl alcohol amination with a primary amine as a nitrogen source.</caption><thead><tr><th>Entry</th><th>Catalyst</th><th>T (°C)</th><th>t (h)</th><th>Solvent</th><th>Additive</th><th>Yield (%)</th><th>Ref</th></tr></thead><tbody><tr><td>1</td><td>[Ru<sub>3</sub>CO<sub>12</sub>]/CataCXiumPCy®</td><td>110</td><td>24</td><td>Neat</td><td>—</td><td>66</td><td>[25]</td></tr><tr><td>2</td><td>Ru-PNO complex</td><td>110–130</td><td>4</td><td>Neat</td><td>t-BuOK</td><td>68</td><td>[26]</td></tr><tr><td>3</td><td>Ru-NHC</td><td>120</td><td>24</td><td>Toluene</td><td>t-BuOK</td><td>93</td><td>[27]</td></tr><tr><td>4</td><td>[Ir<sub>2</sub>Cp*]<sub>2</sub></td><td>115</td><td>10</td><td>H<sub>2</sub>O</td><td>—</td><td>86</td><td>[28]</td></tr><tr><td>5</td><td>Cyclometalated Iridium complex</td><td>80</td><td>24</td><td>H<sub>2</sub>O</td><td>KOH</td><td>91</td><td>[29]</td></tr><tr><td>6</td><td>Mn-NNS complex</td><td>140</td><td>72</td><td>Toluene</td><td>KOH</td><td>67<sup>1</sup></td><td>[30]</td></tr><tr><td>7</td><td>Ti<sup>III</sup><sub>0.2</sub>Ti<sup>IV</sup><sub>0.8</sub>(NTf<sub>2</sub>)<sub>2</sub>(O)<sub>x</sub>(OH)<sub>y</sub>(H<sub>2</sub>O)<sub>z</sub>·2.5H<sub>2</sub>O</td><td>100</td><td>2</td><td>Toluene</td><td>Bipyridine or terpyridine</td><td>98<sup>2</sup></td><td>[31]</td></tr><tr><td>8</td><td>Nanosized zeolite beta</td><td>135</td><td>4</td><td>Neat</td><td>—</td><td>52</td><td>[32]</td></tr><tr><td>9</td><td>PdZn/Al<sub>2</sub>O<sub>3</sub></td><td>110</td><td>4</td><td>p-xylene</td><td>—</td><td>85</td><td>[33]</td></tr><tr><td>10</td><td>[Ni(COD)<sub>2</sub>]</td><td>140</td><td>18</td><td>CPME</td><td>KOH</td><td>51</td><td>[14]</td></tr></tbody></table>

<footnote n="1">¹ A diamine was used as a nitrogen source. ² The reaction was performed under microwave irradiation. Cp* is the classical abbreviation for pentamethylcyclopentadiene.</footnote>
<figure><img src="image_13.png" /><figcaption>**Scheme 10.** Amination of furfuryl alcohol with aniline.</figcaption></figure>

In addition to the homogeneous systems already described, heterogeneous catalysts were used to perform this reaction (Table 2 Entry 7–10). The most efficient catalyst is the complex Ti<sup>III</sup><sub>0.2</sub>Ti<sup>IV</sup><sub>0.8</sub>(NTf<sub>2</sub>)<sub>2</sub>(O)<sub>x</sub>(OH)<sub>y</sub>(H<sub>2</sub>O)<sub>z</sub>·2.5H<sub>2</sub>O (Table 2 Entry 7) [31]. Indeed, only 2 h were required at 100 °C in the presence of bipyridine or terpyridine as ligands under microwave irradiations to reach a 98% yield of the targeted amines. Interestingly, the authors are proposing an SN-type mechanism rather than the classical borrowing hydrogen one, which is classically encountered in alcohol amination. The ligand may help to solubilize the catalyst, avoiding its deactivation and increasing its activity by forming cationic species. Zeolites were also used as catalysts and their catalytic activity was ascribed to the acidity of the catalyst (Table 2 Entry 8) [32]. The first step of the mechanism is assumed to be the adsorption of the alcohol on the acid sites of the zeolite for further reaction with the amine, thus increasing its reactivity. Oxophilic catalysts such as PdZn/Al<sub>2</sub>O<sub>3</sub> were effective for this transformation (Table 2 Entry 9) [33]. The alcohol is believed to be alkylated on the surface of the PdZn catalyst. Indeed, the oxophilic nature of Zn atoms played a crucial role in the reaction, whereas Pd atoms are azophilic. This may explain the high catalytic activity of the intermetallic PdZn/Al<sub>2</sub>O<sub>3</sub> catalyst.

When a diamine was used as a substrate, the corresponding 2,3-dihydro-1H-perimidine derivative was formed (Scheme 11, Table 2 Entry 6) [30]. This sustainable system, comprising a nontoxic earth-abundant manganese complex and an air- and moisture-stable ligand scaffold, could afford a 67% yield of the desired compound.

<figure><img src="image_14.png" /><figcaption>**Scheme 11.** Amination of furfuryl alcohol with 1,8-diaminonaphthalene.</figcaption></figure>

Note that Huynh et al. used a cationic Ru-NHC catalyst [RuCl(*p*-cymene)(NHC)(PPh<sub>3</sub>))[PF<sub>6</sub>] to perform the amidation of furfuryl alcohol in the presence of NaH as a base (Scheme 12) [34]. Interestingly, the nature of the base influences the nature of the product formed. The amidation reaction was effective only in the presence of a strong base otherwise, the formation of the expected amine was observed.

<figure><img src="image_15.png" /><figcaption>**Scheme 12.** Furfuryl alcohol amidation.</figcaption></figure>
## Tertiary Amines as Nitrogen Sources

There is only one example of tertiary amines synthesized from furfuryl alcohol reported in the literature [35]. The use of [RuCl₃·3H₂O] and 1,10-bis(diphenylphosphino)ferrocene (dppf) allowed for the alkylation of a tertiary amine at a good yield (Scheme 13). Interestingly, the amination agent was a tertiary amine. The reaction afforded a mixture of mono- and bis-substituted products with a preference for the mono-substituted product.

<figure><img src="image_16.png" /><figcaption>**Scheme 13.** Tertiary amines synthesis from furfuryl alcohol.</figcaption></figure>

### 2.3.2. 1-(2-Furyl)ethanol

Under the same conditions used for furfuryl alcohol, the amination of 1-(2-furyl)ethanol was investigated. The reaction was performed with a primary amine or with ammonia as nitrogen sources, leading to the formation of a secondary or primary amine respectively. Both reactions proceeded using [Ru₃CO₁₂] in combination with CataCXium® PCy as catalyst (Scheme 14) [18,25].

<figure><img src="image_17.png" /><figcaption>**Scheme 14.** 1-(2-furyl)ethanol amination.</figcaption></figure>

### 2.3.3. 5-Methylfurfuryl Alcohol

Similar to that which was reported with furfuryl alcohol, in 2019, Barta et al. performed the amination of 5-methylfurfuryl alcohol using Ni/Al₂O₃-SiO₂ as a catalyst to provide 45% of the desired primary amine (Scheme 15) [22].

<figure><img src="image_18.png" /><figcaption>**Scheme 15.** 5-methylfurfuryl alcohol amination.</figcaption></figure>

### 2.3.4. 5-(Hydroxymethyl)furfural

The compound 2,5-bisaminomethylfuran (2,5-BAMF) can be formed starting with either 5-(hydroxymethyl)furfural (5-HMF) [21,36,37] or 2,5-bis(hydroxymethyl)furan (BHMF) (see below) [20,36].

When 5-HMF was used as a substrate, the reaction combined a reductive amination of the carbonyl moiety and the borrowing hydrogen methodology on the alcohol function. Whereas it was possible to perform selectively the reductive amination of the carbonyl function, selective transformation of the alcohol function has never been observed. This is presumably due to the increased reactivity of the carbonyl group compared to the alcohol and to the similar reaction conditions needed to undergo both reductive amination and hydrogen borrowing reactions. This shows the selectivity limit of the use of natural substrates with hydrogen borrowing methodology. As an example, a stepwise amination of 5-HMF was described in 2017 by Hara [38]. The reductive amination of the aldehyde
function was performed by Ru/Nb₂O₅ using ammonia as a nitrogen source. No amination of the alcohol function was observed. It was necessary to perform the amination of this amino alcohol with [Ru(CO)ClH(PPh₃)₃]/Xantphos to yield the desired diamine at a yield of 93%.

However, the formation of 2,5-BAMF starting from 5-HMF can be performed using either homogeneous (Table 3 Entry 1) or heterogeneous catalysts (Table 3 Entry 2–3). All systems required the use of external H₂ as an additive.

<table><caption>**Table 3.** Catalytic amination of 5-HMF with ammonia as a nitrogen source to produce 2,5-BAMF.</caption><thead><tr><th>Entry</th><th>Catalyst</th><th>T (°C)</th><th>t (h)</th><th>Solvent</th><th>Additive</th><th>Yield (%)</th><th>Refs</th></tr></thead><tbody><tr><td>1</td><td>Ru-PNP complex</td><td>140</td><td>11</td><td>t-amyl alcohol</td><td>H₂ (10 bar)</td><td>85</td><td>[36]</td></tr><tr><td>2</td><td>RANEY® Ni</td><td>160</td><td>12</td><td>THF</td><td>H₂ (10 bar)</td><td>61</td><td>[21]</td></tr><tr><td>3</td><td>CuNiAlOₓ</td><td>210¹</td><td>27</td><td>Dioxane</td><td>Na₂CO₃<br>H₂ (45 bar)</td><td>86</td><td>[37,39,40]</td></tr></tbody></table>

Homogeneous catalysts proved to be efficient with complete conversion in the reaction of 5-HMF with ammonia using 10 bar H₂ and t-amyl alcohol as solvent at 140 °C for 11 h (Scheme 16, Table 3 Entry 1) [36].

<figure><img src="image_19.png" /><figcaption>**Scheme 16.** Homogeneous amination of 5-HMF.</figcaption></figure>

Several heterogeneous catalysts were also tested for this reaction: RANEY® Ni, RANEY® Co, CuNiAlOₓ Pd/C, Pt/C, and Ru/C [21,37,39,40]. Whereas Pd/C, Pt/C, and Ru/C were only efficient for reductive amination of the carbonyl moiety, RANEY® Ni was effective for 5-HMF diamination with a 61% yield (Table 3 Entry 2) [21]. The catalytic activity could be increased to 86% with the use of the bifunctional CuNiAlOₓ catalyst (Scheme 17, Table 3 Entry 3) [37,39,40]. This catalyst combined the hydrogenation ability of Ni with the dehydrogenation ability of Cu. A base was used as an additive to promote the hydrogen transfer reaction. A gradual heating of the reaction was necessary to achieve high selectivity. Indeed, the reductive amination of the aldehyde only required 90 °C heating for 9 h, whereas the hydrogen borrowing of the alcohol required 210 °C for 18 h.

<figure><img src="image_20.png" /><figcaption>**Scheme 17.** Heterogeneous amination of 5-HMF.</figcaption></figure>

Only one example of 5-HMF amination using primary amines as nitrogen sources was described by Pera-Titus et al. [41]. A mechanical mixture of 5%Ru/C + 5%Pd/C catalysts or a bifunctional (Ru + Pd)/C were required to afford more than an 87% yield of

<footnote n="1">¹ 9 h at 90 °C, followed by 18 h at 210 °C.</footnote>
diamines (Scheme 18). The reaction consists of two consecutive steps: the aerobic oxidation of HMF to 2,5-diformylfuran, followed by reductive amination of 2,5-diformylfuran to the corresponding diamines in the presence of H₂. Even though the reaction cannot be categorized as a hydrogen borrowing reaction, the overall chemical equation is a reductive amination of the carbonyl and the amination of the alcohol of HMF in a one-step process and shall therefore be mentioned here.

<figure><img src="image_21.png" /><figcaption>**Scheme 18.** Tandem oxidation-amination reaction of 5-HMF.</figcaption></figure>

### 2.3.5. 2,5-Bis(hydroxymethyl)furan

The compound 2,5-bis(hydroxymethyl)furan (BHMF) was used as a substrate in amination reactions with ammonia as a nitrogen source to produce 2,5-bis(aminomethyl)furan (BAMF) using either homogeneous or heterogeneous catalysts [20,36]. For homogeneous reaction, the amination of the alcohol moieties was observed with an 85% yield after 9 h (Scheme 19) [36]. The heterogeneous system provided a similar yield since 86% of BAMF was obtained when Ru–MgO/TiO₂ was used as a catalyst [20].

<figure><img src="image_22.png" /><figcaption>**Scheme 19.** Homogeneous amination of BHMF.</figcaption></figure>

### 2.4. Polyfunctional Alcohols

Alcohols found in nature are often bearing multiple functionalities, for this reason, the reaction conditions should be adapted to the specificities of other groups that may also be reactive. The amination is complex due to the functional group, which may hinder the coordination sites of the catalyst. In some cases, the functional groups can also be reactive, as shown with the aldehyde function of 5-HMF, which is more reactive than the alcohol function. We will here take α-hydroxy amides, α-hydroxy acids, and α-/β-hydroxy esters as examples of bifunctional molecules.

#### 2.4.1. α-hydroxy Amides

The first amination of α-hydroxy amides was reported in 2011 by Beller et al. [42]. The reaction went well when [Ru₃(CO)₁₂] was used as a metallic precursor with 1,2-bis(dicyclohexylphosphino)ethane as a ligand in t-amyl alcohol at 160 °C for 24 h, yielding 91% (Scheme 20). The reaction was quite tolerant to the substituent borne by the amine and by the α-hydroxy amides, even though the yields decreased to 20% when both alcohol and nitrogen sources were sterically hindered. Alternatively, [TiCl₄] could be used stoichiometrically at only 100 °C, instead of the Ru based catalyst, to provide the desired α-amino amides with moderate to good yields [43].
<figure><img src="image_23.png" /><figcaption>**Scheme 20.** α-hydroxy amides amination.</figcaption></figure>

### 2.4.2. α-hydroxy Acids

α-hydroxy acids can be transformed into α-amino acids in one step with high yields using ruthenium nanoparticles supported on carbon nanotubes or on nitrogen-doped carbon nanotubes as catalysts [44–46]. This methodology provides an alternative to the classical microbial cultivation process used for α-amino acids production. It seems, however, limited to the transformation of α-hydroxy acids since the use of β-hydroxy acids only led to poor yields (below 4%). Doping the carbon nanotubes with nitrogen led to an increase in catalytic activity. This enhancement is believed to be due to the improvement of the Ru nanoparticle dispersion on the support and to their strong interaction with the support. Additionally, the absorption of the substrate is believed to be facilitated when a N-dopant is used.

Changing the catalyst to an ultrathin CdS nanosheet using $NH_3$ under visible light irradiation provides the formation of the desired α-amino acids at only 50 °C with relatively low yields (Scheme 21) [47]. The formation of oxygen-centered radicals under these conditions is considered to be responsible for the activity of the catalytic system. Unfortunately, once again low activity was detected with β-hydroxy acids (yields below 6%).

<figure><img src="image_24.png" /><figcaption>**Scheme 21.** α-hydroxy acid amination.</figcaption></figure>

### 2.4.3. α-and β-hydroxy Esters

The use of α-hydroxy esters as substrates under reaction conditions which are known to be effective for non-functional alcohols provided a rather unexpected reaction [42]. Indeed, the reaction was selectively performed on the alcohol but also on the ester moiety, with 78% of alanamide observed (Scheme 22). This indicates a low ester tolerance under these conditions.

<figure><img src="image_25.png" /><figcaption>**Scheme 22.** α-hydroxy ester amination.</figcaption></figure>
However, the reaction of ammonia and α-hydroxy esters in the presence of [RuHCl(PPh₃)₃(CO)] and Xantphos resulted in the formation of the desired primary amine in good yields [48]. In the particular case of β-hydroxyl acid esters, the use of a Brønsted acid as an additive was an efficient methodology for their amination with various aniline derivatives [49]. The catalyst and the additive are believed to form adducts which are presumably more active than the catalyst alone (Scheme 23).

<figure><img src="image_26.png" /><figcaption>**Scheme 23.** β-hydroxy esters amination.</figcaption></figure>

## 2.5. Polyols

### 2.5.1. Diols

A large number of publications on the amination of diols can be found in the literature. For this reason, we have selected examples to give a general trend to understand the remaining barriers with this type of substrate. Isohexides will be treated separately as they are complex compounds due to the difference in reactivity between the two hydroxyl groups.

As shown in Scheme 24, amination of diols can lead to a broad structural variety depending on: (i) the substrates used (nitrogen source and/or diol), (ii) the catalysts used, and (iii) the reaction conditions. The main products encountered in this section are the expected diamines, formed by the double amination of the two alcohol functions, and the amino alcohols, arising from the amination of only one alcohol, in line with the cyclization products. This cyclization can be inter- or intra-molecular. On the one hand, a diamine reacts with a diol, thus forming a cycle, and on the other hand, an amino alcohol is formed, and the amine function reacts with the remaining alcohol, thus providing cyclization of the product. Finally, aromatic heterocycles or dehydrated/aminated products can sometimes be obtained. In these reactions, oligomer formation (or at least dimerization) was one of the side reactions often encountered [50–57].

### Diamines and Amino Alcohol Synthesis

The main products of diol amination are diamines. However when the reaction does not go to completion, the formation of amino alcohols was observed. Homogeneous and heterogeneous catalysts leading to diamination and/or monoamination of diols are reported in Table 4. Several factors influence the reactivity of the catalytic system, and the important parameters will be reviewed herein with selected examples. Note that the reaction could also provide the formation of an amino ketone when the reaction proceeds further than amino alcohol formation without going to completion [58].
<figure><img src="image_27.png" /><figcaption>**Scheme 24.** Diol amination.</figcaption></figure>

**Nature of the alcohols:** primary alcohols were found to be much more reactive than secondary ones. When primary and secondary alcohol diols were combined, amino-alcohols were formed instead of the corresponding diamines [59,60]. This shows the increased activity of primary alcohols toward secondary ones and the importance of the steric hindrance of alcoholic substrates [59]. However, under certain conditions, the reactivity of secondary alcohols can be pushed to complete the reaction. Stepwise amination of primary and secondary diols was also performed and was significantly faster with primary alcohols compared to secondary ones (Scheme 25) [61].

<figure><img src="image_28.png" /><figcaption>**Scheme 25.** Stepwise amination of diol.</figcaption></figure>

The selectivity of the reaction was also driven by the length/nature of the spacer between the two alcohol functions [62] and its steric hindrance [63]. For example, the use of an *O*-tethered spacer led to the formation of amino-alcohols, whereas the use of a simple aliphatic chain gave diamines [62].

**Nature of the nitrogen sources:** in addition to the nature of the alcohol substrates, the selectivity of the reaction strongly depends on the steric hindrance of the nitrogen sources (Scheme 26) [64]. It was demonstrated that, within a homogeneous process catalyzed by [RuCl₂(PPh₃)₂], highly sterically hindered amines preferentially provided the formation of amino alcohols, while the use of small nitrogen sources allowed access to diaminated compounds.
<figure><img src="image_29.png" /><figcaption>**Scheme 26.** Effect of the steric parameter on selectivity.</figcaption></figure>

<table><caption>**Table 4.** Typical catalysts used for diol amination.</caption><thead><tr><th></th><th>Diamination</th><th>Monoamination</th></tr></thead><tbody><tr><td rowspan="14">Heterogeneous Catalysts</td><td>zeolite</td><td>zeolites</td></tr><tr><td>Ni-Cu-Cr<sub>2</sub>O<sub>3</sub></td><td>Ni-Cu-Cr<sub>2</sub>O<sub>3</sub></td></tr><tr><td>Ru/Co/Al<sub>2</sub>O<sub>3</sub></td><td>Ru/Co/Al<sub>2</sub>O<sub>3</sub></td></tr><tr><td>Ru-Co-Sn</td><td>Ru-Co-Sn</td></tr><tr><td>CuNiAlO<sub>x</sub></td><td>CuNiAlO<sub>x</sub></td></tr><tr><td>Re-Ru-Co</td><td>Re-Ru-Co</td></tr><tr><td>Co-Fe</td><td>Co-Fe</td></tr><tr><td>Cu-Zn-Zr oxide</td><td>Cu-Zn-Zr oxide</td></tr><tr><td>Cu/Al<sub>2</sub>O<sub>3</sub></td><td>Cu/Al<sub>2</sub>O<sub>3</sub></td></tr><tr><td>Cu-Ni-Ca-Ba</td><td>Ni nanoparticles</td></tr><tr><td>Pt-Sn/γ-Al<sub>2</sub>O<sub>3</sub></td><td>CuCrO</td></tr><tr><td>Ru/Al<sub>2</sub>O<sub>3</sub></td><td>RhIn/C</td></tr><tr><td>Ru/C</td><td>Co/γ-Al<sub>2</sub>O<sub>3</sub></td></tr><tr><td>Re-Ru-Co</td><td></td></tr><tr><td>RANEY® Ni</td><td></td></tr><tr><td>Co-Fe</td><td></td></tr><tr><td rowspan="14">Homogeneous Catalysts</td><td>[RuCl<sub>3</sub>·xH<sub>2</sub>O]</td><td>[RuCl<sub>3</sub>·xH<sub>2</sub>O]/PPh<sub>3</sub></td></tr><tr><td>[RuCl<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub>]</td><td>[RuCl<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub>]</td></tr><tr><td>[Ru<sub>3</sub>(CO)<sub>12</sub>]/</td><td>[Ru<sub>3</sub>(CO)<sub>12</sub>]/</td></tr><tr><td>CataCXium PCy</td><td>CataCXium PCy</td></tr><tr><td>[RuCl(p-cymene)(P,N)]</td><td>[RuCl(p-cymene)(P,N)]</td></tr><tr><td>[Cl]</td><td>[Cl]</td></tr><tr><td>[IrCl<sub>2</sub>Cp*(NHC)]</td><td>[IrCl<sub>2</sub>Cp*(NHC)]</td></tr><tr><td>[Ru<sub>3</sub>(CO)<sub>12</sub>]/ PNP</td><td>[Ru<sub>3</sub>(CO)<sub>12</sub>]/ PNP</td></tr><tr><td>[IrCl<sub>3</sub>·xH<sub>2</sub>O]/PPh<sub>3</sub></td><td>[RuHCl(PPh<sub>3</sub>)<sub>3</sub>]</td></tr><tr><td>[RuHCl(CO)(PPh<sub>3</sub>)<sub>3</sub>]/</td><td>[RuHCl(CO)(PPh<sub>3</sub>)<sub>3</sub>]/</td></tr><tr><td>Xantphos</td><td>Triphos</td></tr><tr><td></td><td>[RuCl<sub>2</sub>(p-cymene)]<sub>2</sub>/</td><td>[DPEphos]</td></tr><tr><td></td><td>[RuCl<sub>2</sub>(p-cymene)]<sub>2</sub>/</td><td>[Josiphos]</td></tr><tr><td></td><td>[IrH<sub>2</sub>Cl((iPr<sub>2</sub>PC<sub>2</sub>H<sub>4</sub>)<sub>2</sub>NH)]</td><td>[Fe(CO)<sub>4</sub>]</td></tr><tr><td></td><td>(cyclopentadienone)]</td><td>[Fe(CO)<sub>4</sub>]</td></tr></tbody></table>

**Reaction conditions:** the reaction temperature was found to be a critical parameter [72,90]. For example, in 1987, the amination of 1,6-hexanediol was performed at temperatures ranging from 165 to 230 °C. A mixture of diamines and aminols was always obtained. However, selectivity toward amino-alcohols is increased at low temperatures (up to 90% at 180 °C) and selectivity toward diaminated products increases with temperature (up to 65% at 230 °C) [72]. This temperature dependence is commonly observed [67,83]. The selectivity also strongly depends on the catalyst loading [69]. In the case of a heterogeneous process, the nature of the support, is also of capital importance. Li et al. showed that basic (Ru/MgO) and neutral (Ru/Al<sub>2</sub>O<sub>3</sub>) supported catalysts were efficient for monoammonia reactions, whereas acidic supported catalysts (Ru/Nb<sub>2</sub>O<sub>5</sub>) provided mainly diaminated products (in line with by-products formation) [51].

**Stoichiometry:** in addition to the amination of one of the alcohol moiety, a dehydration of the second alcohol and subsequent hydrogenation can sometimes be observed [16,50,81].
The quantity of amines plays a crucial role in the latter transformation. Hence, the use of an excess of amines led to the formation of the expected diamines, preventing the dehydration reaction (Scheme 27). Similar dehydration reactions were observed in the absence of amine [50].

<figure><img src="image_30.png" /><figcaption>**Scheme 27.** Dehydration reaction.</figcaption></figure>

## Cyclization Reactions

Cyclized compounds could also be obtained as products owing to the presence of two alcohol functions on the same molecule. Cyclization could either be inter- or intra-molecular depending on the nitrogen sources used (Scheme 28). The homogeneous and heterogeneous catalysts leading to the cyclization of diols are reported in Table 5.

<figure><img src="image_31.png" /><figcaption>**Scheme 28.** Cyclization reactions.</figcaption></figure>

<table><caption>**Table 5.** Typical catalysts used for diol cyclization.</caption><thead><tr><th></th><th>Intermolecular Cyclization</th><th></th><th>Intramolecular Cyclization</th><th></th></tr></thead><tbody><tr><td rowspan="15">Heterogeneous Catalysts</td><td>Pt-Sn/γ-Al<sub>2</sub>O<sub>3</sub></td><td>[62]</td><td>Pt-Sn/γ-Al<sub>2</sub>O<sub>3</sub></td><td>[62,91]</td></tr><tr><td>Pd/MgO</td><td>[92]</td><td>zeolites</td><td>[65,66,93–95]</td></tr><tr><td></td><td></td><td>Re-Ru-Co</td><td>[70]</td></tr><tr><td></td><td></td><td>NiCuFeO<sub>x</sub></td><td>[96]</td></tr><tr><td></td><td></td><td>CuNiAlO<sub>x</sub></td><td>[69]</td></tr><tr><td></td><td></td><td>(Ni<sub>0.5</sub>Cu<sub>0.5</sub>)Fe<sub>2</sub>O<sub>4</sub></td><td>[97]</td></tr><tr><td></td><td></td><td>Cu-Zn-Zr oxide</td><td>[71]</td></tr><tr><td></td><td></td><td>CuCrO</td><td>[75]</td></tr><tr><td></td><td></td><td>Ru/Co/Al<sub>2</sub>O<sub>3</sub></td><td>[67]</td></tr><tr><td></td><td></td><td>Ru-Co-Sn</td><td>[68]</td></tr><tr><td></td><td></td><td>Ni/Co/Cu/Sn/Al<sub>2</sub>O<sub>3</sub></td><td>[98]</td></tr><tr><td></td><td></td><td>Ru/C</td><td>[78]</td></tr></tbody></table>
<table><caption>**Table 5.** *Cont.*</caption><thead><tr><th></th><th>Intermolecular Cyclization</th><th>Intramolecular Cyclization</th></tr></thead><tbody><tr><td rowspan="10">Homogeneous Catalysts</td><td>[Fe(CO)<sub>4</sub> (cyclopentadienone)]<br/>[IrCl<sub>2</sub>Cp*]<sub>2</sub><br/>[RuCl(p-cymene)(P,N)]<br/>[Cl]</td><td>[Fe(CO)<sub>4</sub> (cyclopentadienone)]<br/>[IrCl<sub>2</sub>Cp*]<sub>2</sub><br/>[RuCl(p-cymene)(P,N)]<br/>[Cl]</td></tr><tr><td>[RuCl<sub>2</sub>(p-cymene)]<sub>2</sub>/DPEphos</td><td>[RuCl<sub>3</sub>·xH<sub>2</sub>O]/PPh<sub>3</sub></td></tr><tr><td>[Pd(OAc)<sub>2</sub>]/PPh<sub>3</sub></td><td>[RuCl<sub>2</sub>(PPh<sub>3</sub>)<sub>3</sub>]<br/>[RuCl(p-cymene)<br/>(NHC)(PPh<sub>3</sub>)][PF<sub>6</sub>]<br/>[RuCl<sub>2</sub>(PPh<sub>3</sub>)<br/>(C<sub>5</sub>H<sub>3</sub>N-2,6-(CH<sub>2</sub>NMe<sub>2</sub>)<sub>2</sub>]<br/>Ru-PNP complex</td></tr><tr><td></td><td>[RuHCl(CO)(PPh<sub>3</sub>)<sub>3</sub>]/<br/>Triphos</td></tr><tr><td></td><td>[Ru(acac)<sub>3</sub>]/Triphos</td></tr><tr><td></td><td>cyclometalated Ir catalyst</td></tr><tr><td></td><td>[CuBr<sub>2</sub>]</td></tr><tr><td></td><td>1,3,5-triazo-2,4,6-triphosphorine-<br/>2,2,4,4,6,6-hexachloride<br/>(TAPC)</td></tr></tbody></table>

On the one hand, diols can react with diamines to promote the cyclization process, thus providing an intermolecular reaction. In this case, two nitrogen atoms are comprised in the newly formed cycle when [Fe(CO)<sub>4</sub>(cyclopentadienone)] is used as a catalyst (Scheme 29).

<figure><img src="image_32.png" /><figcaption>**Scheme 29.** Intermolecular cyclization.</figcaption></figure>

On the other hand, cyclization occurred by reaction of the newly formed amine with the second alcohol function of the starting diols, thus providing a heterocycle with only one nitrogen atom. A critical parameter in the cyclization is the stability of the cycle formed. Cycles comprising of five or six atoms are the most common, even though seven-atom rings were also reported (Scheme 30) [62].

<figure><img src="image_33.png" /><figcaption>**Scheme 30.** Intramolecular cyclization.</figcaption></figure>

**Nature of the amines:** the nature of the amines used was of prime importance for the cyclization. As an example, the use of unsubstituted benzylamine led to the formation of an amino alcohol, whereas the chloro-substituted one led to a high yield of cycle products [89], highlighting the importance of electronic density on the nitrogen sources.
**Nature of the alcohols:** the cyclization reaction also seems to be sensitive to steric hindrance of the alcohol substrates used, as shown by Madsen et al. [55]. Although [IrCl₂Cp*]₂, can efficiently convert ethylene glycol into the corresponding piperazine in the presence of a catalytic amount of base (isolated yields from 35 to 86%), no dimerization was observed when phenylethylene glycol and cyclohexane-1,2-diol were used as substrates.

One example of morpholine derivatives formation was reported from the intermolecular amination of ethanolamine. A 75% yield was obtained from the reaction of ethyleneglycol and NH₃ in the presence of a NiO/CuO/TiO₂/Cr₂O₃ catalyst under an H₂ atmosphere [111].

## Aromatic Heterocycles Formation

**Pyrrole:** coupling amines with unsaturated 1,4-diols led to the formation of pyrrole using [Fe(CO)₃(cyclopentadienone)] as a catalyst (Scheme 31) [56,112]. Trimethylamine N-oxide (Me₃NO) was used as an additive to generate the catalytically active species. Alternatively, [RuH₂(CO)(PPh₃)₃]/Xantphos could be used to provide pyrroles without the use of additives [113]. The reaction is believed to proceed via preliminary isomerization of the 1,4-alkylediol into a 1,4-diketone followed by a Paal–Knorr cyclization. Similar reactivity was observed with the reaction of ketones, vicinal diols, and amines in the presence of [Ru₃(CO)₁₂]/Xantphos or [Ru(p-cymene)Cl₂]₂/Xantphos as catalysts [114,115].

<figure><img src="image_34.png" /><figcaption>**Scheme 31.** Pyrrole formation.</figcaption></figure>

**Pyrazine and phenazine:** amination of 1,2-cyclooctanediol led to the formation of a mixture of dicycloocta[b,e]pyrazine and dicycloocta[b,e]-2,3-dihydropyrazine [16]. A similar behavior was observed with 1,2-cyclohexanediol, yielding octahydrophenazine upon reaction with [Ru₃(CO)₁₂]/acridine-based diphosphine (Scheme 32).

<figure><img src="image_35.png" /><figcaption>**Scheme 32.** 1,2-cyclohexanediol amination.</figcaption></figure>
### 2.5.2. Isohexides

Isohexides are obtained from sorbitol dehydration. For this biogenic diol, three isomers can be found. To the best of our knowledge, only examples of isosorbide and isomannide aminations have been reported in the literature. Either one or the two alcohols can be aminated (Scheme 33). Amination often leads to isomerization of the aminated position due to the carbonyl/imine intermediates which comprise a sp² carbon atom, thus leading to a loss of the chiral information. Isosorbide isomerization to isoidide or isomannide instead of amination was often observed, highlighting the particular and challenging nature of this substrate. Note that isosorbide isomerization is also known to occur in the presence of a Ru catalyst and under H₂ pressure [116].

<figure><img src="image_36.png" /><figcaption>**Scheme 33.** Isohexide amination products.</figcaption></figure>

#### Ammonia as a Nitrogen Source

The first report on isohexide amination was published by Beller in 2011 [48]. They reported the amination of isosorbide with ammonia to provide the corresponding primary diamine (Scheme 34, Table 6 Entry 1). No details were given on the stereoselectivity of the reaction.

<figure><img src="image_37.png" /><figcaption>**Scheme 34.** Isosorbide amination.</figcaption></figure>

<table><caption>**Table 6.** Catalytic isohexides diamination using ammonia as a nitrogen source.</caption><thead><tr><th>Entry</th><th>Catalyst</th><th>T (°C)</th><th>t (h)</th><th>Solvent</th><th>Additive</th><th>Yield (%)</th><th>Refs</th></tr></thead><tbody><tr><td>1</td><td>[RuHCl(CO)(PPh<sub>3</sub>)<sub>3</sub>]/Xantphos</td><td>150</td><td>20</td><td>t-amyl alcohol</td><td>—</td><td>96</td><td>[48]</td></tr><tr><td>2</td><td>[RuHCl(CO)(POP)]</td><td>170</td><td>48</td><td>t-amyl alcohol</td><td>—</td><td>90</td><td>[117]</td></tr><tr><td>3</td><td>[Ru<sub>3</sub>(CO)<sub>12</sub>]/PNP</td><td>170–200</td><td>21</td><td>t-amyl alcohol</td><td>—</td><td>96</td><td>[16,118]</td></tr><tr><td>4</td><td>[RuHCl(CO)(PNP)]</td><td>170</td><td>48</td><td>t-amyl alcohol</td><td>—</td><td>90</td><td>[119]</td></tr></tbody></table>
Excellent yields were obtained by Vogt with isomannide by using a mixture of [Ru<sub>3</sub>(CO)<sub>12</sub>] and the acridine-based diphosphine developed by Milstein as a catalyst at 170 °C (Scheme 35, Table 6 Entry 3) [16]. In this case, a mixture of diamino-isosorbide/diamino-isomannide/diamoisoidide in a 45, 15, and 35% yield was obtained, respectively (total conversion = 96%). This isomer distribution corresponds to the thermodynamic equilibrium expected at this temperature. The authors highlighted the importance of using an excess of ammonia for the reaction to proceed to an acceptable yield with correct kinetics.

<figure><img src="image_38.png" /><figcaption>**Scheme 35.** Isomannide amination.</figcaption></figure>

In 2014, the amination of isosorbide and isomannide was patented by Schelwies et al. using a homogeneous Ru-based catalyst (Scheme 36, Table 6 Entry 3 and Table 7 Entry 1) [118]. Excellent conversions of 99% were obtained, and the selectivity of the reaction toward mono- or di-amination was tuned according to the nature of the catalysts and to the reaction conditions (concentration, stoichiometry, and pressure). Selectivity of up to 94% for mono-amination and up to 96% for di-amination was achieved.

<figure><img src="image_39.png" /><figcaption>**Scheme 36.** Isosorbide and isomannide mono- and di-amination.</figcaption></figure>

<table><caption>**Table 7.** Catalytic isohexides mono-amination using ammonia as a nitrogen source.</caption><thead><tr><th>Entry</th><th>Catalyst</th><th>T (°C)</th><th>t (h)</th><th>Solvent</th><th>Additive</th><th>Yield (%)</th><th>Refs</th></tr></thead><tbody><tr><td>1</td><td>[RuHCl(CO)<br>(PNP)]</td><td>180</td><td>20</td><td>t-amyl alcohol</td><td>—</td><td>94</td><td>[118]</td></tr><tr><td>2</td><td>[RuHCl(CO)<br>(PPh<sub>3</sub>)<sub>3</sub>]</td><td>150</td><td>20</td><td>Neat</td><td>—</td><td>50</td><td>[48]</td></tr><tr><td>3</td><td>Ru/C</td><td>170</td><td>24</td><td>H<sub>2</sub>O</td><td>H<sub>2</sub> (10 bar)</td><td>50</td><td>[78,120,121]</td></tr><tr><td>4</td><td>RANEY® Ni</td><td>160</td><td>18</td><td>t-amyl alcohol</td><td>—</td><td>32</td><td>[22]</td></tr><tr><td>5</td><td>Ni/Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub></td><td>160</td><td>18</td><td>t-amyl alcohol</td><td>—</td><td>51</td><td>[22]</td></tr></tbody></table>

The catalytic activity of several heterogeneous catalysts was assessed in isohexide amination but only resulted in mono-aminations (Table 7 Entry 3–5). As an example, Rose et al. described the synthesis of aminoalcohol or isomerization reactions using Ru/C
as a catalyst [78,120,121]. The moderate conversion of the reaction highlights the complexity of the catalytic system. No diastereoselectivity was observed in this case since a mixture of the *endo* and *exo* amino alcohols were obtained. Both isosorbide and isomannide were used as substrates in the course of this study [120,121]. Both substrates gave rise to different reactivities, presumably due to the configuration of the hydroxyl groups in both isomers. It was found that the *endo*-configured alcohols were more reactive due to the lower activation barrier on the Ru/C catalyst and to their higher accessibility. Slight hydrogen pressure was beneficial for the reaction, even though increasing the pressure led to an increase in the isomerization. To the best of our knowledge, only one other report regarding the use of heterogeneous catalysts was published using RANEY® Ni or Ni/Al₂O₃-SiO₂ to obtain moderate yields of the mono aminated product (32 and 51% respectively) [22]. No details were given concerning the regioselectivity of the reaction.

## Primary Amines as Nitrogen Sources

With the aim of reducing the number of by-products formed and to gain a better understanding of the selectivity of the reaction, partially protected isohexides were used as substrates. In 2018, Popowycz and collaborators studied the stereoselective amination of an *exo*-monobenzylated isosorbide, which will reduce the number of by-products due to the reduced number of alcohol functions available for the BH reaction [122]. The activity of classical Ru-based homogeneous catalysts was limited even when a base was used as an additive. The catalytic activity was drastically increased using [IrCl₂Cp*]₂. The best results were finally obtained by using the well-defined Ir catalyst depicted in Scheme 37, along with diphenyl phosphate as an additive. Less nucleophilic or hindered amines led to a lower yield of the aminated product. Interestingly, the reaction gave similar results, independently of the orientation of the benzyloxy group, i.e., with excellent diastereoselectivity, highlighting the spectator role of the C6 position. This was the first report concerning the controlled stereochemistry of the product formed. When *endo*-benzyloxy-isosorbide, which comprises the alcohol function at the *exo* configuration, was used as substrate, no reaction was observed, thus pointing to the disfavored reaction at *exo* positions.

<figure><img src="image_40.png" /><figcaption>**Scheme 37.** Monobenzylated isosorbide amination.</figcaption></figure>

When unprotected isosorbide was used as a substrate under similar conditions, only one isomer was formed with yields ranging from 11 to 71% (Scheme 38) [123]. The reaction of isomannide with various amines led to the formation of the desired diamine in a stereoselective fashion with a 47–79% yield (Scheme 38).
<figure><img src="image_41.png" /><figcaption>**Scheme 38.** Isosorbide and isomannide amination over a homogeneous Ir catalyst.</figcaption></figure>

The use of isohexide as a substrate is a challenging task in hydrogen borrowing reactions. Indeed, as shown before, the presence of two alcohol functions on the same substrate can lead to unexpected reactions and to uncompleted amination. Even though side reactions were not observed, amination selectivity is challenging. The main hurdle here is to succeed in the amination of both alcohol functions. Whereas monoaminated and diaminated products can now be obtained depending on reaction conditions with both isomannide and isosorbide, further research is still required to achieve stereoselective reactions.

### 2.5.3. Triols

The most available biobased triol is glycerol since it is a by-product of biodiesel production. As shown in Scheme 39, a large structural variety of products were achieved via dehydration reactions, partial aminations, amine formylations, condensations, cyclizations, and C-C bond cleavages.

<figure><img src="image_42.png" /><figcaption>**Scheme 39.** Glycerol amination.</figcaption></figure>

The first amination of glycerol was reported in 2014 by Crotti et al. [124]. They reacted glycerol with a diamine to perform an intermolecular cyclization reaction. Due to the high number of alcohol functions on the substrate, the reaction provided a mixture of N-heterocyclic compounds (Scheme 40).
<figure><img src="image_43.png" /><figcaption>**Scheme 40.** Glycerol intermolecular cyclization.</figcaption></figure>

The other cyclic compound that can be formed by glycerol amination is oxazoline (Scheme 41) [125]. Indeed, Ru/C was able to achieve 95% selectivity to oxazoline (27% conversion). A mechanism was proposed involving the preliminary formation of acetol by glycerol dehydration followed by imine formation and finally a reaction of the imine with a second acetol molecule to achieve the formation of oxazoline.

<figure><img src="image_44.png" /><figcaption>**Scheme 41.** Oxazoline formation from glycerol and ammonia.</figcaption></figure>

Glycerol amination was then reported by Katryniok et al. in 2016 [126]. They used salts of phosphomolybdic acid as catalysts to yield (dimethylamino)acetone by the N-acetonylation reaction of dimethylamine with glycerol. The conversion can be increased by up to 33% by supporting the catalyst on silica, which leads to an increase in the catalyst acidity. A mechanism was proposed for the formation of (dimethylamino)acetone from glycerol as depicted in Scheme 42. A similar reactivity was reported the same year with improved yields (up to 94%) [127]. A homogeneous Ru catalyst could also be used to perform this reaction under acid conditions with yields of up to 81% [128].

<figure><img src="image_45.png" /><figcaption>**Scheme 42.** (dimethylamino)acetone synthesis.</figcaption></figure>

In addition to the formation of N-Acetonyl amine over the CuNiAlOₓ catalyst, glycerol could also be used as a methylation agent for various amines (Scheme 43) [127]. The reactivity was driven by the solvent, i.e., use of pure 1,4-dioxane led to the formation of N-Acetonyl amines, whereas a mixture of water and 1,4-dioxane provided methylated amines. Finally, performing the reaction under 5 bar of O₂ led to the formation of amides through a formylation reaction (Scheme 43) [127]. This highlights the versatility of glycerol as a substrate and the importance of the reaction conditions in this type of reaction. Indeed, small changes lead to the formation of different products.
<figure><img src="image_46.png" /><figcaption>**Scheme 43.** Glycerol reactivity over a CuNiAlOₓ catalyst.</figcaption></figure>

Alanine production was also possible in a 43% yield, starting from glycerol over a RuNi/MgO catalyst in aqueous ammonia (Scheme 44) [129]. The glycerol was believed to be first transformed into lactic acid, which then was aminated to alanine.

<figure><img src="image_47.png" /><figcaption>**Scheme 44.** Alanine formation from glycerol.</figcaption></figure>

C-C bond cleavages were also observed upon glycerol amination. Glycerol was transformed into a mixture of methyl amine, ethyl amine, and propylamine by reaction with aqueous ammonia under H₂ pressure over Ru/C [130]. Other chemicals such as 2,6-dimethylpiperazine, piperazine, 2-methylpiperazine, and various alcoholic products were observed as by-products. However, a selectivity of 51% in alkyl amines could be obtained after optimization of the reaction conditions. Finally, glycerol was used to perform N-hydroxyethylation of amines in basic media (Scheme 45) [128,131]. The proposed mechanism for this reaction involves C-C bond cleavage via dehydrogenation and retroal-dol/decarbonylation sequences.

<figure><img src="image_48.png" /><figcaption>**Scheme 45.** Glycerol as an N-hydroxyethylation agent.</figcaption></figure>

As shown here, the expected product in which all alcohol functions are aminated has not been observed yet. To perform the amination only at one position, it is necessary to protect glycerol by forming solketal (Scheme 46) [132]. The product could easily be deprotected afterward.
<figure><img src="image_49.png" /><figcaption>**Scheme 46.** Solketal amination.</figcaption></figure>

Only two examples of amination of other triols than glycerol have been reported, both led to cyclization reactions. When 1,5,9-nonanetriol was used as substrate in the presence of [Ir(NH₃)₃Cp*][I]₂, the formation of quinolizidine was observed (Scheme 47) [133]. The cyclization occurred with an 85% yield in a very selective fashion, highlighting the efficiency of the reaction.

<figure><img src="image_50.png" /><figcaption>**Scheme 47.** 1,5,9-nonanetriol amination.</figcaption></figure>

The amination of 1,2,4-butanetriol has also been studied in detail [134]. Again, cyclization was observed with [RuCl₂(*p*-cymene)]₂/Xantphos in the presence of a base (Scheme 48). One of the hydroxyl groups remained intact after the reaction. The extension of this methodology to 1,3,4-hexanetriol and 1,2,5-pentanetriol led to the formation of 2-ethyl pyrrolidinol and an equimolar mixture of pyrrolidine/piperidine respectively.

<figure><img src="image_51.png" /><figcaption>**Scheme 48.** 1,2,4-butanetriol amination.</figcaption></figure>

### 2.5.4. Carbohydrates

Carbohydrates can be obtained from cellulose/hemicellulose depolymerization under acid conditions. Carbohydrates often comprise a reactive aldehyde or ketone function that can be masked in their closed ring form. This function is prone to reductive amination and can be protected to facilitate the reactivity of the less reactive alcohol functions in amination reactions. Additionally, protection steps can be added to trigger the reactivity of a particular alcohol function. In this section, we will thus differentiate between protected and unprotected carbohydrates.

#### Protected Carbohydrates

The first report of carbohydrate amination was published in 2011 by Cumpstey and Martín-Matute [135]. As shown in Scheme 49, the amination of protected α-mannose was achieved using [IrCl₂Cp*]₂ as a catalyst. Interestingly, the amination agent was a carbohydrate amine, thus providing pseudodisaccharide in the presence of a base. All the products were isolated as only one diastereoisomer. A good selectivity toward the primary C6 alcohol was achieved (71% of product).

The carbohydrate amine could also be used in combination with other alcohols with good yields. Note that the unprotected amino sugar could also react with various alcohols to provide alkylated amines with no oligomer formation (Scheme 50). This highlights the lower reactivity of the alcohols borne by secondary carbons on the carbohydrate. In this case, toluene could not be used as a solvent due to solubility issues. The reaction was thus performed using the alcohol as a solvent. These reactions could also be performed using glucose derivatives instead of mannose, producing a yield of 44–78%.
<figure><img src="image_52.png" /><figcaption>**Scheme 49.** Amination of protected carbohydrates.</figcaption></figure>

<figure><img src="image_53.png" /><figcaption>**Scheme 50.** An amino sugar is used as a nitrogen source in a hydrogen borrowing strategy.</figcaption></figure>

## Unprotected Carbohydrates

The use of protected carbohydrates led to the selective formation of the desired products. However, several synthesis steps were added to perform the synthesis of the alcoholic substrates. As shown in Scheme 51, the use of unprotected carbohydrates only led to C-C bond cleavages in line with the results obtained with glycerol. However, even when C-C bond cleavages were observed, good selectivities and conversions in various amines and amino alcohols were obtained.

<figure><img src="image_54.png" /><figcaption>**Scheme 51.** Unprotected carbohydrate amination.</figcaption></figure>

Note that N-heterocyclic chemical formation from unprotected carbohydrates am-
ination is well described, these reactions are not considered borrowing hydrogen be-
cause the amination usually occurs on carbonyl functions, and thus will not be reported
here [136–141].

The authors of [142,143] describe the use of a series of monosaccharides such as
glucose, fructose, 2-deoxy-D-glucose, and xylose in combination with Ru/C as a catalyst
to provide C2-diamines (Scheme 52, Table 8 Entry 1). In the course of these reactions, the
presence of H₂ pressure was mandatory to avoid decomposition of the starting materials
and to obtain complete reactions (i.e., the formation of diaminated products instead of monoaminated). The proposed mechanism involved a hemiaminal formation followed by an iminium formation by dehydration. A C-C cleavage on the latter, followed by a hydrogenation reaction thus formed the amine. Supported Ni catalysts also allowed the reaction to perform nicely (up to a 92% yield, Table 8 Entry 2). A large series of monomeric substrates were used under these conditions, such as mannose, galactose, or arabinose. Interestingly, trimeric carbohydrates and disaccharides could also be used (cellobiose, maltose, and maltotriose), with a decrease in the yield indicating poor hydrolysis of the glycosidic linkages.

<figure><img src="image_55.png" /><figcaption>**Scheme 52.** C2-diamine formation from glucose amination over Ru/C.</figcaption></figure>

<table><caption>**Table 8.** Catalytic amination of unprotected carbohydrates.</caption><thead><tr><th>Entry</th><th>Catalyst</th><th>T (°C)</th><th>t (h)</th><th>Solvent</th><th>Additive</th><th>Products</th><th>Refs</th></tr></thead><tbody><tr><td>1</td><td>Ru/C</td><td>125</td><td>1</td><td>H<sub>2</sub>O</td><td>H<sub>2</sub> (70 bar)</td><td>Ethan-diamines</td><td>[142,143]</td></tr><tr><td>2</td><td>Supported Ni</td><td>125</td><td>1</td><td>H<sub>2</sub>O</td><td>H<sub>2</sub> (70 bar)</td><td>Ethan-diamines</td><td>[142,143]</td></tr><tr><td>3</td><td>[Ru(2-methylallyl)<sub>2</sub>(cod)<sub>2</sub>]/ Xantphos</td><td>150</td><td>16</td><td>Dioxane</td><td>Acetic acid</td><td>Ethanol-amines</td><td>[131]</td></tr><tr><td>4</td><td>[RuCl<sub>2</sub>(p-cymene)]/DCyPF/N-MeTMA</td><td>150</td><td>20</td><td>Dioxane</td><td>t-BuOK</td><td>Ethanol-amines</td><td>[128]</td></tr><tr><td>5</td><td>CdS nanosheet</td><td>50</td><td>8</td><td>H<sub>2</sub>O</td><td>NaOH, hv</td><td>Alanine</td><td>[47]</td></tr></tbody></table>

Chaudhari described in 2018 the amination of sorbitol (a compound obtained via the hydrogenation of glucose) using a similar Ru/C catalyst under H₂ pressure and observed the formation of a complex mixture of aliphatic amines (10% methylamine, 11% ethylamine, 12% propylamine, and 15% other alcoholic products) with excellent conversion. These results highlight the C-C cleavages occurring during the course of the reaction, thus forming smaller carbon chains similar to that which was observed with glycerol (Scheme 53) [130].

<figure><img src="image_56.png" /><figcaption>**Scheme 53.** Sorbitol amination.</figcaption></figure>

Carbohydrates were used to perform hydroxyethylation of amines [128,131]. The skeleton of the carbohydrate was cleaved similar to work by Sels et al. [142,143]. Two homogeneous systems enabling the formation of β-amino alcohols from amines and carbohydrates were described in the literature. The use of [Ru(2-methylallyl)<sub>2</sub>(cod)<sub>2</sub>] and Xantphos allow the transformation of various C5 and C6 sugars, as well as oligomeric carbohydrates, in the presence of acid derivatives, even though lower yields were obtained with oligosaccharides (Scheme 54). Only traces of product were obtained when cellulose was used as a substrate. Interestingly, pre-treatment of α-cellulose with inorganic acids for further hydroxyethylation reaction led to the formation of the desired β-amino alcohols.
The second system enabling the reaction was described in 2020, and allowed the reaction to be performed in basic media instead of under acidic conditions as reported in 2019 (Table 8 Entry 4) [128].

<figure><img src="image_57.png" /><figcaption>**Scheme 54.** Hydroxyethylation of amines from glucose.</figcaption></figure>

Finally, a photocatalytic conversion of glucose into alanine was performed over an ultrathin CdS nanosheet (Scheme 55) [47]. Even though low amounts of alanine were isolated, conversion to the key intermediate, namely lactic acid, was observed.

<figure><img src="image_58.png" /><figcaption>**Scheme 55.** Alanine formation.</figcaption></figure>

As shown in this section, the alcohol protection of carbohydrates to deactivate several positions for amination reactions or the use of aminated carbohydrates as amination agents were the only routes to access more complex structures. Indeed, without these strategies, C-C bond cleavages were always observed even though selective reactions could occur under specific conditions (Table 8). Carbohydrate amination has not yet been achieved under acceptable conditions since tremendous protection steps are required to avoid C-C bond cleavages of the carbohydrate structure. Research in this field is still limited, and more effort could be devoted to uncovering new reaction conditions that could alleviate the protection procedure and achieve carbohydrate amination instead of decomposition.

**3. Conclusions: Challenges and Future Directions**

In this review, we provide an overview of the most significant advances in the use of bio-based alcohols with the hydrogen borrowing approach (Scheme 56). We discussed the versatility of the available catalysts and demonstrated the most recent advancements in the use of biobased substrates. Despite its incontestable success, highlighted by the increased number of publications in the last decade, several hurdles remain.

Some of the bio-based substrates, such as the fatty alcohols, are successfully converted to the corresponding amines. It appears that the presence of a long aliphatic chain has no impact on the efficiency of the reaction. When terpenoids are used as substrates, selectivity issues are observed due to the presence of C=C double bonds, which leads to the formation of enals, which can then isomerize. Additionally, when bulky terpenoids are used, the reaction does not go to completion and the formation of the intermediate ketone as the main product is observed instead of the expected amines. In the case of furan derivatives, despite efficient conditions reported for the formation of the desired amines, several by-products are obtained. Reduction of the furan cycle is indeed observed, such as amidation reactions. The selectivity toward furan cycle reduction is driven by the presence of external H₂ pressure, whereas the selectivity toward an amidation reaction (instead of amination) is driven by the presence of a strong base. This highlights the importance of the reaction
conditions. Interestingly, the use of 5-HMF only leads to di-amination reactions since it is not possible to selectively aminate the alcohol functions without affecting the carbonyl moiety. However, 2,5-BAMF is selectively obtained from 5-HMF or BHMF even though H₂ pressure is required. For polyfunctional alcohols, ester functions are compatible with hydrogen borrowing methodology even though, under certain conditions, α-amino acid amides are obtained by di-amination of the corresponding α-hydroxy esters. Additionally, whereas amination of α-hydroxy acids is efficient, β-hydroxy acids only leads to poor yields.

<figure><img src="image_59.png" /><figcaption>**Scheme 56.** Overview of the use of bio-based alcohol with the hydrogen borrowing approach.</figcaption></figure>

A large number of publications are dealing with polyols since they are one of the predominant classes of alcoholic compounds found in nature or that can be obtained from biomass. A broad structural diversity is achieved when polyols are used as substrates in amination reactions. Indeed, aside from the expected diamines, incomplete reactions are observed with the formation of the corresponding amino alcohols, such as cyclization reactions or even the formation of aromatic heterocycles or dehydrated/aminated products. The selectivity of the reaction is driven by the substrates used (nitrogen sources and/or diols), the catalytic systems, or the reaction conditions. The selectivity of these reactions can be considered as the main hurdle for the expansion of the use of this methodology with bio-based substrates. The most striking example of this lack of selectivity is the use of carbohydrate, which only leads to C-C bond cleavages of the carbohydrate backbone unless the alcohol functions are all protected.

Additionally, to pursue efforts for milder reaction conditions and lower catalyst loading, efforts targeting the special needs for bio-based substrates still need to be made. Various catalysts have been used for this purpose, either homogeneous or heterogeneous. However, most of them comprise noble metallic centers, which are expensive and environmentally harmful. We are thus anticipating the breakthrough of an earth-abundant based catalyst, which is still limited when it comes to natural substrates. Additionally, within this review, we have highlighted the strong dependence between the selectivity of the reaction and either the catalyst structure/nature or the reaction conditions. We have indeed identified selectivity as one of the main issues to circumvent for the amination of bio-based alcohols. We strongly believe that the tuning of the catalyst structure and the adaptation of the reaction conditions to the pre-requisite of the use of natural substrates is the way to overcome this hurdle. The design of a more active catalyst will also allow milder reaction conditions such as the decrease of the reaction temperature or the use of additives, which are critical parameters for the reaction selectivity. Even though hydrogen borrowing is a powerful strategy to provide C-N bond formation, only a few examples of stereo controlled reactions have been described [144], and the reports concerning the asymmetric amination of bio-based substrates are still scarce. This is critical in order to apply this methodology to higher-value product formation, such as pharmaceutical drug
precursors. Additionally, several catalytic systems still require the use of an external H₂ source, which is not mandatory when a borrowing hydrogen mechanism is involved. More active catalysts which are less prone to oxidation are thus required.

In conclusion, with this overview, bio-based alcohols can be aminated in only one step to provide highly desirable products. A high atom economy is achieved within this reaction since water is the only by-product formed. However, we find that selectivity and functional group tolerance are the main issues to circumvent. We hope that further research on sustainable catalysis will promote bio-based alcohol amination as a new route for biomass valorization.

**Author Contributions:** Writing—review and editing, S.H. and K.D.O.V.; resources, H.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by "Région Nouvelle Aquitaine": SACCHOIL.

**Acknowledgments:** This work pertains to the French government program "Investissements d'Avenir" (EUR INTREE, reference ANR-18-EURE-0010). The authors acknowledge financial support from the European Union (ERDF) and Région Nouvelle Aquitaine. The authors acknowledge the INCREASE Federation.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

## References

1. Esposito, D.; Antonietti, M. Redefining Biorefinery: The Search for Unconventional Building Blocks for Materials. *Chem. Soc. Rev.* **2015**, *44*, 5821–5835. [CrossRef] [PubMed]

2. Corma, A.; Iborra, S.; Velty, A. Chemical Routes for the Transformation of Biomass into Chemicals. *Chem. Rev.* **2007**, *107*, 2411–2502. [CrossRef] [PubMed]

3. Trowbridge, A.; Walton, S.M.; Gaunt, M.J. New Strategies for the Transition-Metal Catalyzed Synthesis of Aliphatic Amines. *Chem. Rev.* **2020**, *120*, 2613–2692. [CrossRef] [PubMed]

4. He, J.; Chen, L.; Liu, S.; Song, K.; Yang, S.; Riisager, A. Sustainable Access to Renewable N-Containing Chemicals from Reductive Amination of Biomass-Derived Platform Compounds. *Green Chem.* **2020**, *22*, 6714–6747. [CrossRef]

5. Corma, A.; Navas, J.; Sabater, M.J. Advances in One-Pot Synthesis through Borrowing Hydrogen Catalysis. *Chem. Rev.* **2018**, *118*, 1410–1459. [CrossRef]

6. Reed-Berendt, B.G.; Latham, D.E.; Dambatta, M.B.; Morrill, L.C. Borrowing Hydrogen for Organic Synthesis. *ACS Cent. Sci.* **2021**, *7*, 570–585. [CrossRef] [PubMed]

7. Podyacheva, E.; Afanasyev, O.I.; Vasilyev, D.V.; Chusov, D. Borrowing Hydrogen Amination Reactions: A Complex Analysis of Trends and Correlations of the Various Reaction Parameters. *ACS Catal.* **2022**, *12*, 7142–7198. [CrossRef]

8. Rahimpour, M.R.; Dehnavi, M.R.; Allahgholipour, F.; Iranshahi, D.; Jokar, S.M. Assessment and Comparison of Different Catalytic Coupling Exothermic and Endothermic Reactions: A Review. *Appl. Energy* **2012**, *99*, 496–512. [CrossRef]

9. Guillena, G.; Ramón, D.J.; Yus, M. Hydrogen Autotransfer in the N-Alkylation of Amines and Related Compounds Using Alcohols and Amines as Electrophiles. *Chem. Rev.* **2010**, *110*, 1611–1641. [CrossRef]

10. Winans, C.F.; Adkins, H. The Alkylation of Amines as Catalyzed by Nickel. *J. Am. Chem. Soc.* **1932**, *54*, 306–312. [CrossRef]

11. Grigg, R.; Mitchell, T.R.B.; Sutthivaiyakit, S.; Tongpenyai, N. Transition Metal-Catalysed N-Alkylation of Amines by Alcohols. *J. Chem. Soc. Chem. Commun.* **1981**, *12*, 611–612. [CrossRef]

12. Watanabe, Y.; Tsuji, Y.; Ohsugi, Y. The Ruthenium Catalyzed N-Alkylation and N-Heterocyclization of Aniline Using Alcohols and Aldehydes. *Tetrahedron Lett.* **1981**, *22*, 2667–2670. [CrossRef]

13. Edwards, M.G.; Jazzar, R.F.R.; Paine, B.M.; Shermer, D.J.; Whittlesey, M.K.; Williams, J.M.J.; Edney, D.D. Borrowing Hydrogen: A Catalytic Route to C–C Bond Formation from Alcohols. *Chem. Commun.* **2004**, *1*, 90–91. [CrossRef] [PubMed]

14. Afanasenko, A.; Elangovan, S.; Stuart, M.C.A.; Bonura, G.; Frusteri, F.; Barta, K. Efficient Nickel-Catalysed N-Alkylation of Amines with Alcohols. *Catal. Sci. Technol.* **2018**, *8*, 5498–5505. [CrossRef]

15. Paudel, K.; Xu, S.; Hietsoi, O.; Pandey, B.; Onuh, C.; Ding, K. Switchable Imine and Amine Synthesis Catalyzed by a Well-Defined Cobalt Complex. *Organometallics* **2021**, *40*, 418–426. [CrossRef]

16. Pingen, D.; Diebolt, O.; Vogt, D. Direct Amination of Bio-Alcohols Using Ammonia. *ChemCatChem* **2013**, *5*, 2905–2912. [CrossRef]

17. Gunanathan, C.; Milstein, D. Selective Synthesis of Primary Amines Directly from Alcohols and Ammonia. *Angew. Chem.* **2008**, *120*, 8789–8792. [CrossRef]

18. Imm, S.; Bähn, S.; Neubert, L.; Neumann, H.; Beller, M. An Efficient and General Synthesis of Primary Amines by Ruthenium-Catalyzed Amination of Secondary Alcohols with Ammonia. *Angew. Chem. Int. Ed.* **2010**, *49*, 8126–8129. [CrossRef]
19. Liang, G.; Zhou, Y.; Zhao, J.; Khodakov, A.Y.; Ordomsky, V.V. Structure-Sensitive and Insensitive Reactions in Alcohol Amination over Nonsupported Ru Nanoparticles. *ACS Catal.* **2018**, *8*, 11226-11234. [CrossRef]

20. Kita, Y.; Kuwabara, M.; Yamadera, S.; Kamata, K.; Hara, M. Effects of Ruthenium Hydride Species on Primary Amine Synthesis by Direct Amination of Alcohols over a Heterogeneous Ru Catalyst. *Chem. Sci.* **2020**, *11*, 9884-9890. [CrossRef]

21. Zhou, K.; Liu, H.; Shu, H.; Xiao, S.; Guo, D.; Liu, Y.; Wei, Z.; Li, X. A Comprehensive Study on the Reductive Amination of 5-Hydroxymethylfurfural into 2,5-Bisaminomethylfuran over Raney Ni Through DFT Calculations. *ChemCatChem* **2019**, *11*, 2649-2656. [CrossRef]

22. Liu, Y.; Afanasenko, A.; Elangovan, S.; Sun, Z.; Barta, K. Primary Benzylamines by Efficient N-Alkylation of Benzyl Alcohols Using Commercial Ni Catalysts and Easy-to-Handle Ammonia Sources. *ACS Sustain. Chem. Eng.* **2019**, *7*, 11267-11274. [CrossRef] [PubMed]

23. Ye, X.; Plessow, P.N.; Brinks, M.K.; Schelwies, M.; Schaub, T.; Rominger, F.; Paciello, R.; Limbach, M.; Hofmann, P. Alcohol Amination with Ammonia Catalyzed by an Acridine-Based Ruthenium Pincer Complex: A Mechanistic Study. *J. Am. Chem. Soc.* **2014**, *136*, 5923-5929. [CrossRef] [PubMed]

24. Liu, Y.; Zhou, K.; Shu, H.; Liu, H.; Lou, J.; Guo, D.; Wei, Z.; Li, X. Switchable Synthesis of Furfurylamine and Tetrahydrofurfurylamine from Furfuryl Alcohol over RANEY® Nickel. *Catal. Sci. Technol.* **2017**, *7*, 4129-4135. [CrossRef]

25. Hollmann, D.; Tillack, A.; Michalik, D.; Jackstell, R.; Beller, M. An Improved Ruthenium Catalyst for the Environmentally Benign Amination of Primary and Secondary Alcohols. *Chem.–Asian J.* **2007**, *2*, 403–410. [CrossRef] [PubMed]

26. Lee, C.-C.; Chu, W.-Y.; Liu, Y.-H.; Peng, S.-M.; Liu, S.-T. Coordination and Catalytic Activity of Ruthenium Complexes Containing Tridentate P,N,O Ligands. *Eur. J. Inorg. Chem.* **2011**, *2011*, 4801–4806. [CrossRef]

27. Kaloğlu, M.; Gürbüz, N.; Sémeril, D.; Özdemir, İ. Ruthenium(II)-(p-Cymene)-N-Heterocyclic Carbene Complexes for the N-Alkylation of Amine Using the Green Hydrogen Borrowing Methodology. *Eur. J. Inorg. Chem.* **2018**, *2018*, 1236–1243. [CrossRef]

28. Saidi, O.; Blacker, A.J.; Farah, M.M.; Marsden, S.P.; Williams, J.M.J. Iridium-Catalysed Amine Alkylation with Alcohols in Water. *Chem. Commun.* **2010**, *46*, 1541–1543. [CrossRef]

29. Luo, N.; Zhong, Y.; Wen, H.; Luo, R. Cyclometalated Iridium Complex-Catalyzed N-Alkylation of Amines with Alcohols via Borrowing Hydrogen in Aqueous Media. *ACS Omega* **2020**, *5*, 27723–27732. [CrossRef]

30. Das, K.; Mondal, A.; Pal, D.; Srivastava, H.K.; Srimani, D. Phosphine-Free Well-Defined Mn(I) Complex-Catalyzed Synthesis of Amine, Imine, and 2,3-Dihydro-1H-Perimidine via Hydrogen Autotransfer or Acceptorless Dehydrogenative Coupling of Amine and Alcohol. *Organometallics* **2019**, *38*, 1815–1825. [CrossRef]

31. Payard, P.-A.; Finidori, C.; Guichard, L.; Cartigny, D.; Corbet, M.; Khrouz, L.; Bonneviot, L.; Wischert, R.; Grimaud, L.; Pera-Titus, M. Rational Optimization of Lewis-Acid Catalysts for Direct Alcohol Amination, Part 2–Titanium Triflimide as New Active Catalyst. *Eur. J. Org. Chem.* **2020**, *2020*, 3225–3228. [CrossRef]

32. Reddy, M.M.; Kumar, M.A.; Swamy, P.; Naresh, M.; Srujana, K.; Satyanarayana, L.; Venugopal, A.; Narender, N. N-Alkylation of Amines with Alcohols over Nanosized Zeolite Beta. *Green Chem.* **2013**, *15*, 3474–3483. [CrossRef]

33. Furukawa, S.; Suzuki, R.; Komatsu, T. Selective Activation of Alcohols in the Presence of Reactive Amines over Intermetallic PdZn: Efficient Catalysis for Alcohol-Based N-Alkylation of Various Amines. *ACS Catal.* **2016**, *6*, 5946–5953. [CrossRef]

34. Xie, X.; Huynh, H.V. Tunable Dehydrogenative Amidation versus Amination Using a Single Ruthenium-NHC Catalyst. *ACS Catal.* **2015**, *5*, 4143–4151. [CrossRef]

35. Luo, J.; Wu, M.; Xiao, F.; Deng, G. Ruthenium-Catalyzed Direct Amination of Alcohols with Tertiary Amines. *Tetrahedron Lett.* **2011**, *52*, 2706–2709. [CrossRef]

36. Pingen, D.; Schwaderer, J.B.; Walter, J.; Wen, J.; Murray, G.; Vogt, D.; Mecking, S. Diamines for Polymer Materials via Direct Amination of Lipid- and Lignocellulose-Based Alcohols with NH₃. *ChemCatChem* **2018**, *10*, 3027–3033. [CrossRef]

37. Yuan, H.; Kusema, B.T.; Yan, Z.; Streiff, S.; Shi, F. Highly Selective Synthesis of 2,5-Bis(Aminomethyl)Furan via Catalytic Amination of 5-(Hydroxymethyl)Furfural with NH₃ over a Bifunctional Catalyst. *RSC Adv.* **2019**, *9*, 38877–38881. [CrossRef]

38. Komanoya, T.; Kinemura, T.; Kita, Y.; Kamata, K.; Hara, M. Electronic Effect of Ruthenium Nanoparticles on Efficient Reductive Amination of Carbonyl Compounds. *J. Am. Chem. Soc.* **2017**, *139*, 11493–11499. [CrossRef]

39. Li, P.; LIEBENS, A.T. A Process for Producing a Tetrahydrofuran Compound Comprising at Least Two Amine Functional Groups. WO Patent WO2018113599A1, 28 June 2018.

40. Li, P.; Liebens, A.T.; Shi, F.; Yuan, H. Process for Production of Aromatic Compounds Comprising at Least Two Amine Functions. U.S. Patent US10662142B2, 26 May 2020.

41. Sha, J.; Kusema, B.T.; Zhou, W.-J.; Yan, Z.; Streiff, S.; Pera-Titus, M. Single-Reactor Tandem Oxidation–Amination Process for the Synthesis of Furan Diamines from 5-Hydroxymethylfurfural. *Green Chem.* **2021**, *23*, 7093–7099. [CrossRef]

42. Zhang, M.; Imm, S.; Bähn, S.; Neumann, H.; Beller, M. Synthesis of α-Amino Acid Amides: Ruthenium-Catalyzed Amination of α-Hydroxy Amides. *Angew. Chem. Int. Ed.* **2011**, *50*, 11197–11201. [CrossRef]

43. Chandgude, A.L.; Dömling, A. Direct Amination of α-Hydroxy Amides. *Asian J. Org. Chem.* **2017**, *6*, 981–983. [CrossRef] [PubMed]

44. Deng, W.; Wang, Y.; Zhang, S.; Gupta, K.M.; Hülsey, M.J.; Asakura, H.; Liu, L.; Han, Y.; Karp, E.M.; Beckham, G.T.; et al. Catalytic Amino Acid Production from Biomass-Derived Intermediates. *Proc. Natl. Acad. Sci. USA* **2018**, *115*, 5093–5098. [CrossRef] [PubMed]
45. Xie, Z.; Chen, B.; Peng, F.; Liu, M.; Liu, H.; Yang, G.; Han, B. Highly Efficient Synthesis of Amino Acids by Amination of Bio-Derived Hydroxy Acids with Ammonia over Ru Supported on N-Doped Carbon Nanotubes. *ChemSusChem* **2020**, *13*, 5683–5689.
[CrossRef] [PubMed]

46. Zhang, T. Chemical Transformation of Sugars into Amino Acids. *Chin. J. Catal.* **2018**, *39*, 1013. [CrossRef]

47. Song, S.; Qu, J.; Han, P.; Hülsey, M.J.; Zhang, G.; Wang, Y.; Wang, S.; Chen, D.; Lu, J.; Yan, N. Visible-Light-Driven Amino Acids Production from Biomass-Based Feedstocks over Ultrathin CdS Nanosheets. *Nat. Commun.* **2020**, *11*, 4899. [CrossRef] [PubMed]

48. Imm, S.; Bähn, S.; Zhang, M.; Neubert, L.; Neumann, H.; Klasovsky, F.; Pfeffer, J.; Haas, T.; Beller, M. Improved Ruthenium-Catalyzed Amination of Alcohols with Ammonia: Synthesis of Diamines and Amino Esters. *Angew. Chem. Int. Ed.* **2011**, *50*, 7599–7603. [CrossRef]

49. Afanasenko, A.; Yan, T.; Barta, K. Amination of β-Hydroxyl Acid Esters via Cooperative Catalysis Enables Access to Bio-Based β-Amino Acid Esters. *Commun. Chem.* **2019**, *2*, 1–9. [CrossRef]

50. Lacroix, S.D.; Pennycook, A.; Liu, S.; Eisenhart, T.T.; Marr, A.C. Amination and Dehydration of 1,3-Propanediol by Hydrogen Transfer: Reactions of a Bio-Renewable Platform Chemical. *Catal. Sci. Technol.* **2012**, *2*, 288–290. [CrossRef]

51. Li, Y.; Cheng, H.; Zhang, C.; Zhang, B.; Liu, T.; Wu, Q.; Su, X.; Lin, W.; Zhao, F. Reductive Amination of 1,6-Hexanediol with Ru/Al₂O₃ Catalyst in Supercritical Ammonia. *Sci. China Chem.* **2017**, *60*, 920–926. [CrossRef]

52. Jenzer, G.; Mallat, T.; Baiker, A. Cobalt-catalyzed Amination of 1,3-cyclohexanediol and 2,4-pentanediol in Supercritical Ammonia. *Catal. Lett.* **1999**, *61*, 111–114. [CrossRef]

53. Fischer, A.; Maciejewski, M.; Bürgi, T.; Mallat, T.; Baiker, A. Cobalt-Catalyzed Amination of 1,3-Propanediol: Effects of Catalyst Promotion and Use of Supercritical Ammonia as Solvent and Reactant. *J. Catal.* **1999**, *183*, 373–383. [CrossRef]

54. Rossi, F.V.; Starr, J.T.; Uccello, D.P.; Young, J.A. Synthesis of PEG-Functionalized Amines Using Ruthenium-Catalyzed Hydrogen Borrowing. *Org. Lett.* **2020**, *22*, 5890–5894. [CrossRef] [PubMed]

55. Lorentz-Petersen, L.L.R.; Nordstrøm, L.U.; Madsen, R. Iridium-Catalyzed Condensation of Amines and Vicinal Diols to Substituted Piperazines. *Eur. J. Org. Chem.* **2012**, *2012*, 6752–6759. [CrossRef]

56. Yan, T.; Barta, K. Sustainable Pathways to Pyrroles through Iron-Catalyzed N-Heterocyclization from Unsaturated Diols and Primary Amines. *ChemSusChem* **2016**, *9*, 2321–2325. [CrossRef]

57. Fischer, A.; Mallat, T.; Baiker, A. Synthesis of 1,4-Diaminocyclohexane in Supercritical Ammonia. *J. Catal.* **1999**, *182*, 289–291. [CrossRef]

58. Shimizu, K.; Imaiida, N.; Kon, K.; Hakim Siddiki, S.M.A.; Satsuma, A. Heterogeneous Ni Catalysts for N-Alkylation of Amines with Alcohols. *ACS Catal.* **2013**, *3*, 998–1005. [CrossRef]

59. Bähn, S.; Tillack, A.; Imm, S.; Mevius, K.; Michalik, D.; Hollmann, D.; Neubert, L.; Beller, M. Ruthenium-Catalyzed Selective Monoamination of Vicinal Diols. *ChemSusChem* **2009**, *2*, 551–557. [CrossRef] [PubMed]

60. Watson, A.J.A.; Maxwell, A.C.; Williams, J.M.J. Borrowing Hydrogen Methodology for Amine Synthesis under Solvent-Free Microwave Conditions. *J. Org. Chem.* **2011**, *76*, 2328–2331. [CrossRef]

61. Marichev, K.O.; Takacs, J.M. Ruthenium-Catalyzed Amination of Secondary Alcohols Using Borrowing Hydrogen Methodology. *ACS Catal.* **2016**, *6*, 2205–2210. [CrossRef]

62. Wang, L.; He, W.; Wu, K.; He, S.; Sun, C.; Yu, Z. Heterogeneous Bimetallic Pt–Sn/γ-Al₂O₃ Catalyzed Direct Synthesis of Diamines from N-Alkylation of Amines with Diols through a Borrowing Hydrogen Strategy. *Tetrahedron Lett.* **2011**, *52*, 7103–7107. [CrossRef]

63. Timofeev, A.F.; Bazanov, A.G.; Zubritskaya, N.G. Steric Effects in the Catalytic Amination of γ-, δ-, and ε-Glycols. *Russ. J. Org. Chem.* **2016**, *52*, 1756–1761. [CrossRef]

64. Marsella, J.A. Ruthenium Catalyzed Reactions of Ethylene Glycol with Primary Amines: Steric Factors and Selectivity Control. *J. Organomet. Chem.* **1991**, *407*, 97–105. [CrossRef]

65. Parvulescu, A.-N.; Gordillo, A.; Schroeter, M.K.; Melder, J.-P.; Bechtel, J.; Heidemann, T.; Schunk, S.A.; Müller, U. Process for the Conversion of Ethylene Glycol to Ethylenediamine Employing a Zeolite Catalyst. U.S. Patent US11091425B2, 17 August 2021.

66. Radha Rani, V.; Srinivas, N.; Kulkarni, S.J.; Raghavan, K.V. Amino Cyclization of Terminal (α,ω)-Diols over Modified ZSM-5 Catalysts. *J. Mol. Catal. Chem.* **2002**, *187*, 237–246. [CrossRef]

67. van Cauwenberge, G.; Melder, J.-P.; Hoffer, B.W.; Krug, T.; Pickenäcker, K.; Pape, F.-F.; Schwab, E. Method for Producing Ethylene Amines and Ethanol Amines by the Hydrogenating Amination of Monoethylene Glycol and Ammonia in the Presence of a Catalyst. U.S. Patent US7635790B2, 22 December 2009.

68. Heidemann, T.; BECKER, B.; Koch, E.; Melder, J.-P.; Luyken, H. Method for the Production of Ethyleneamines. U.S. Patent US20200131111A1, 24 May 2020.

69. Wu, Y.; Yuan, H.; Shi, F. Sustainable Catalytic Amination of Diols: From Cycloamination to Monoamination. *ACS Sustain. Chem. Eng.* **2018**, *6*, 1061–1067. [CrossRef]

70. Becker, B.; Heidemann, T.; Bebensee, R.H.; Koch, E.; Melder, J.-P.; Luyken, H.; Oezkozanoglu, C.; Kehrer, J. Method for the Production of Ethyleneamines. WO Patent WO2020178085A1, 26 February 2020.

71. Schroeter, M.K.; Gordillo, A.; Parvulescu, A.-N.; Melder, J.-P.; Pueyo, C.L.; Bechtel, J.; Heidemann, T.; Schunk, S.A.; Mueller, U. Method for Producing Ethanolamines and/or Ethyleneamines. U.S. Patent US10836704B2, 7 December 2020.

72. Vultier, R.; Baikera, A.; Wokaunb, A. Copper Catalyzed Amination of 1,6-Hexanediol. *Appl. Catal.* **1987**, *30*, 167–176. [CrossRef]

73. Runeberg, J.; Baiker, A.; Kijenski, J. Copper Catalyzed Amination of Ethylene Glycol. *Appl. Catal.* **1985**, *17*, 309–319. [CrossRef]
74. Imabeppu, M.; Kiyoga, K.; Okamura, S.; Shoho, H.; Kimura, H. One-Step Amination of α,ω-Alkylenediols over Cu/Ni-Based
Catalysts. *Catal. Commun.* **2009**, *10*, 753–757. [CrossRef]

75. Paden, J.H.; Adkins, H. The Synthesis of Pyrrolidines, Piperidines and Hexahydroazepines1,2. *J. Am. Chem. Soc.* **1936**, *58*,
2487–2499. [CrossRef]

76. Takanashi, T.; Nakagawa, Y.; Tomishige, K. Amination of Alcohols with Ammonia in Water over Rh–In Catalyst. *Chem. Lett.* **2014**, *4*, 822–824. [CrossRef]

77. Takanashi, T.; Tamura, M.; Nakagawa, Y.; Tomishige, K. Structure of Catalytically Active Rh–In Bimetallic Phase for Amination of Alcohols. *RSC Adv.* **2014**, *4*, 28664–28672. [CrossRef]

78. Niemeier, J.; Engel, R.V.; Rose, M. Is Water a Suitable Solvent for the Catalytic Amination of Alcohols? *Green Chem.* **2017**, *19*, 2839–2845. [CrossRef]

79. Lei, X.; Gu, G.; Hu, Y.; Wang, H.; Zhang, Z.; Wang, S. Structural Requirements for Chemoselective Ammonolysis of Ethylene Glycol to Ethanolamine over Supported Cobalt Catalysts. *Catalysts* **2021**, *11*, 736. [CrossRef]

80. Marsella, J.A. Homogeneously Catalyzed Synthesis of Beta-Amino Alcohols and Vicinal Diamines from Ethylene Glycol and 1,2-Propanediol. *J. Org. Chem.* **1987**, *52*, 467–468. [CrossRef]

81. Liu, S.; Rebros, M.; Stephens, G.; Marr, A.C. Adding Value to Renewables: A One Pot Process Combining Microbial Cells and Hydrogen Transfer Catalysis to Utilise Waste Glycerol from Biodiesel Production. *Chem. Commun.* **2009**, *17*, 2308–2310. [CrossRef] [PubMed]

82. Walther, G.; Deutsch, J.; Martin, A.; Baumann, F.-E.; Fridag, D.; Franke, R.; Köckritz, A. α,ω-Functionalized C19 Monomers. *ChemSusChem* **2011**, *4*, 1052–1054. [CrossRef] [PubMed]

83. Schaub, T.; Buschhaus, B.; Brinks, M.K.; Schelwies, M.; Paciello, R.; Melder, J.-P.; Merger, M. Process for Preparing Di-, Tri- and Polyamines by Homogeneously Catalyzed Alcohol Amination. U.S. Patent US8912361B2, 16 December 2014.

84. Schaub, T.; Buschhaus, B.; Brinks, M.K.; Schelwies, M.; Paciello, R.; Melder, J.-P.; Merger, M. Process for the Preparation of Primary Amines by Homogeneously Catalyzed Alcohol Amination. U.S. Patent US20120232309A1, 8 March 2012.

85. Schaub, T.; Buschhaus, B.; Brinks, M.K.; Schelwies, M.; Paciello, R.; Melder, J.-P.; Merger, M. Process for Preparing Di-, Tri- and Polyamines by Homogeneously Catalyzed Alcohol Amination. U.S. Patent US20120232293A1, 8 March 2012.

86. Schaub, T.; Buschhaus, B.; Brinks, M.K.; Schelwies, M.; Paciello, R.; Melder, J.-P.; Merger, M. Process for Preparing Alkanolamines by Homogeneously Catalyzed Alcohol Amination. U.S. Patent US9193666B2, 24 November 2015.

87. Andrushko, N.; Andrushko, V.; Roosevelt, P.; Moonen, K.; Börner, A. Amination of Aliphatic Alcohols and Diols with an Iridium Pincer Catalyst. *ChemCatChem* **2010**, *2*, 640–643. [CrossRef]

88. Yang, L.-C.; Wang, Y.-N.; Zhang, Y.; Zhao, Y. Acid-Assisted Ru-Catalyzed Enantioselective Amination of 1,2-Diols through Borrowing Hydrogen. *ACS Catal.* **2017**, *7*, 93–97. [CrossRef]

89. Yan, T.; Feringa, B.L.; Barta, K. Iron Catalysed Direct Alkylation of Amines with Alcohols. *Nat. Commun.* **2014**, *5*, 5602. [CrossRef]

90. Nordström, L.U.; Madsen, R. Iridium Catalysed Synthesis of Piperazines from Diols. *Chem. Commun.* **2007**, *47*, 5034–5036. [CrossRef]

91. He, W.; Wang, L.; Sun, C.; Wu, K.; He, S.; Chen, J.; Wu, P.; Yu, Z. Pt–Sn/γ-Al₂O₃-Catalyzed Highly Efficient Direct Synthesis of Secondary and Tertiary Amines and Imines. *Chem.–Eur. J.* **2011**, *17*, 13308–13317. [CrossRef]

92. Corma, A.; Ródenas, T.; Sabater, M.J. A Bifunctional Pd/MgO Solid Catalyst for the One-Pot Selective N-Monoalkylation of Amines with Alcohols. *Chem.–Eur. J.* **2010**, *16*, 254–260. [CrossRef] [PubMed]

93. Subba Rao, Y.V.; Kulkarni, S.J.; Subrahmanyam, M.; Ramo Rao, A.V. Modified ZSM-5 Catalysts for the Synthesis of Five- and Six-Membered Heterocyclic Compounds. *J. Org. Chem.* **1994**, *59*, 3998–4000. [CrossRef]

94. Kulkarni, S.J.; Raghavan, K.V.; Vippagunta, R.R.; Nagabandi, S. Process for the Synthesis of an Aliphatic Cyclic Amine. U.S. Patent US6528647B2, 4 March 2003.

95. Long, Y.; Wang, P.; Fei, Y.; Zhou, D.; Liu, S.; Deng, Y. One-Pot Synthesis of N-Methylpyrrolidine (NMPD) Using Cu- and Ni-Modified ZSM-5 as an Efficient Catalyst. *Green Chem.* **2019**, *21*, 141–148. [CrossRef]

96. Cui, X.; Dai, X.; Deng, Y.; Shi, F. Development of a General Non-Noble Metal Catalyst for the Benign Amination of Alcohols with Amines and Ammonia. *Chem.–Eur. J.* **2013**, *19*, 3665–3675. [CrossRef]

97. Li, A.Y.; Dumaresq, N.; Segalla, A.; Braidy, N.; Moores, A. Plasma-Made (Ni₀.₅Cu₀.₅)Fe₂O₄ Nanoparticles for Alcohol Amination under Microwave Heating. *ChemCatChem* **2019**, *11*, 3959–3972. [CrossRef]

98. Chedid, R.B.; Melder, J.-P.; Dostalek, R.; Pastre, J.; Tan, A.M. Process for Preparing Pyrrolidine. U.S. Patent US20140018547A1, 16 January 2014.

99. Fujita, K.; Fujii, T.; Yamaguchi, R. Cp\*Ir Complex-Catalyzed N-Heterocyclization of Primary Amines with Diols: A New Catalytic System for Environmentally Benign Synthesis of Cyclic Amines. *Org. Lett.* **2004**, *6*, 3525–3528. [CrossRef]

100. Swain, S.P.; Shri, O.; Ravichandiran, V. Iridium and Bis(4-Nitrophenyl)Phosphoric Acid Catalysed Amination of Diol by Hydrogen-Borrowing Methodology for the Synthesis of Cyclic Amine: Synthesis of Clopidogrel. *Mol. Catal.* **2021**, *508*, 111576. [CrossRef]

101. Hamid, M.H.S.A.; Allen, C.L.; Lamb, G.W.; Maxwell, A.C.; Maytum, H.C.; Watson, A.J.A.; Williams, J.M.J. Ruthenium-Catalyzed N-Alkylation of Amines and Sulfonamides Using Borrowing Hydrogen Methodology. *J. Am. Chem. Soc.* **2009**, *131*, 1766–1774. [CrossRef]
102. Tsuji, Y.; Huh, K.T.; Ohsugi, Y.; Watanabe, Y. Ruthenium Complex Catalyzed N-Heterocyclization. Syntheses of N-Substituted Piperidines, Morpholines, and Piperazines from Amines and 1,5-Diols. *J. Org. Chem.* **1985**, *50*, 1365–1370. [CrossRef]

103. Shue, Y.-J.; Yang, S.-C.; Lai, H.-C. Direct Palladium(0)-Catalyzed Amination of Allylic Alcohols with Aminonaphthalenes. *Tetrahedron Lett.* **2003**, *44*, 1481–1485. [CrossRef]

104. Felföldi, K.; Klyavlin, M.S.; Bartók, M. Transformation of Organic Compounds in the Presence of Metal Complexes V. Cyclization of Aminoalcohols on a Ruthenium Complex. *J. Organomet. Chem.* **1989**, *362*, 193–195. [CrossRef]

105. Shan, S.P.; Xiaoke, X.; Gnanaprakasam, B.; Dang, T.T.; Ramalingam, B.; Huynh, H.V.; Seayad, A.M. Benzimidazolin-2-Ylidene N-Heterocyclic Carbene Complexes of Ruthenium as a Simple Catalyst for the N-Alkylation of Amines Using Alcohols and Diols. *RSC Adv.* **2014**, *5*, 4434–4442. [CrossRef]

106. Abbenhuis, R.A.T.M.; Boersma, J.; van Koten, G. Ruthenium-Complex-Catalyzed N-(Cyclo)Alkylation of Aromatic Amines with Diols. Selective Synthesis of N-(ω-Hydroxyalkyl)Anilines of Type PhNH(CH₂)NOH and of Some Bioactive Arylpiperazines. *J. Org. Chem.* **1998**, *63*, 4282–4290. [CrossRef]

107. Shi, Y.; Kamer, P.C.J.; Cole-Hamilton, D.J.; Harvie, M.; Baxter, E.F.; Lim, K.J.C.; Pogorzelec, P. A New Route to N-Aromatic Heterocycles from the Hydrogenation of Diesters in the Presence of Anilines. *Chem. Sci.* **2017**, *8*, 6911–6917. [CrossRef] [PubMed]

108. Zou, Q.; Wang, C.; Smith, J.; Xue, D.; Xiao, J. Alkylation of Amines with Alcohols and Amines by a Single Catalyst under Mild Conditions. *Chem.–Eur. J.* **2015**, *21*, 9656–9661. [CrossRef]

109. Bayguzina, A.R.; Musina, C.F.; Khusnutdinov, R.I. N-Alkylation of Aniline and Its Derivatives by Alcohols in the Presence of Copper Compounds. *Russ. J. Org. Chem.* **2018**, *54*, 1652–1659. [CrossRef]

110. Du, Y.; Oishi, S.; Saito, S. Selective N-Alkylation of Amines with Alcohols by Using Non-Metal-Based Acid–Base Cooperative Catalysis. *Chem.–Eur. J.* **2011**, *17*, 12262–12267. [CrossRef]

111. Dobrovolskij, S.V. Verfahren zur herstellung von morpholin. DE Patent DE2758769A1, 12 July 1979.

112. Emayavarmban, B.; Sen, M.; Sundararaju, B. Iron-Catalyzed Sustainable Synthesis of Pyrrole. *Org. Lett.* **2017**, *19*, 6–9. [CrossRef]

113. Pridmore, S.J.; Slatford, P.A.; Daniel, A.; Whittlesey, M.K.; Williams, J.M.J. Ruthenium-Catalysed Conversion of 1,4-Alkynediols into Pyrroles. *Tetrahedron Lett.* **2007**, *48*, 5115–5120. [CrossRef]

114. Zhang, M.; Neumann, H.; Beller, M. Selective Ruthenium-Catalyzed Three-Component Synthesis of Pyrroles. *Angew. Chem. Int. Ed.* **2013**, *52*, 597–601. [CrossRef]

115. Zhang, M.; Fang, X.; Neumann, H.; Beller, M. General and Regioselective Synthesis of Pyrroles via Ruthenium-Catalyzed Multicomponent Reactions. *J. Am. Chem. Soc.* **2013**, *135*, 11384–11388. [CrossRef] [PubMed]

116. Hu, H.; Ramzan, A.; Wischert, R.; Jerôme, F.; Michel, C.; de Vigier, K.O.; Pera-Titus, M. Pivotal Role of H₂ in the Isomerisation of Isosorbide over a Ru/C Catalyst. *Catal. Sci. Technol.* **2021**, *11*, 7973–7981. [CrossRef]

117. Klasovsky, F.; Tacke, T.; Pfeffer, J.C.; Haas, T.; Beller, M.; Martin, A.; Deutsch, J.; Koeckritz, A.; Imm, S.; Haberland, J. Process for the Direct Amination of Alcohols Using Ammonia to Form Primary Amines by Means of a Xantphos Catalyst System. U.S. Patent US8946463B2, 3 February 2015.

118. Schelwies, M.; Brinks, M.; Schaub, T.; Melder, J.-P.; Paciello, R.; Merger, M. Process for the Homogeneously Catalyzed Amination of Alcohols with Ammonia in the Presence of a Complex Catalyst Which Comprises No Anionic Ligands. U.S. Patent US20140024833A1, 23 January 2014.

119. Klasovsky, F.; Pfeffer, J.C.; Tacke, T.; Haas, T.; Martin, A.; Deutsch, J.; Koeckritz, A. Process for the Direct Amination of Secondary Alcohols with Ammonia to Give Primary Amines. U.S. Patent US8927773B2, 6 January 2015.

120. Pfützenreuter, R.; Rose, M. Aqueous-Phase Amination of Biogenic Isohexides by Using Ru/C as a Solid Catalyst. *ChemCatChem* **2016**, *8*, 251–255. [CrossRef]

121. Rose, M.; Palkovits, R.; ENGEL, R.; Begli, A.H.; Kroener, C. Method for the Synthesis of Primary Isohexide Amines. U.S. Patent US9751891B2, 5 September 2017.

122. Jacolot, M.; Moebs-Sanchez, S.; Popowycz, F. Diastereoselective Iridium-Catalyzed Amination of Biosourced Isohexides Through Borrowing Hydrogen Methodology. *J. Org. Chem.* **2018**, *83*, 9456–9463. [CrossRef] [PubMed]

123. Bahé, F.; Grand, L.; Cartier, E.; Jacolot, M.; Moebs-Sanchez, S.; Portinha, D.; Fleury, E.; Popowycz, F. Direct Amination of Isohexides via Borrowing Hydrogen Methodology: Regio- and Stereoselective Issues. *Eur. J. Org. Chem.* **2020**, 599–608. [CrossRef]

124. Crotti, C.; Farnetti, E.; Licen, S.; Barbieri, P.; Pitacco, G. Iridium-Catalyzed N-Alkylation of Diamines with Glycerol. *J. Mol. Catal. Chem.* **2014**, *382*, 64–70. [CrossRef]

125. Pandya, R.; Mane, R.; Rode, C.V. Cascade Dehydrative Amination of Glycerol to Oxazoline. *Catal. Sci. Technol.* **2018**, *8*, 2954–2965. [CrossRef]

126. Safriamin, M.; Paul, S.; Moonen, K.; Ulrichts, D.; Dumeignil, F.; Katryniok, B. Novel Direct Amination of Glycerol over Heteropolyacid-Based Catalysts. *Catal. Sci. Technol.* **2016**, *6*, 2129–2135. [CrossRef]

127. Dai, X.; Rabeaeh, J.; Yuan, H.; Brückner, A.; Cui, X.; Shi, F. Glycerol as a Building Block for Prochiral Aminoketone, N-Formamide, and N-Methyl Amine Synthesis. *ChemSusChem* **2016**, *9*, 3133–3138. [CrossRef]

128. Xin, Z.; Jia, L.; Huang, Y.; Du, C.-X.; Li, Y. Ru-Catalyzed Switchable N-Hydroxyethylation and N-Acetonylation with Crude Glycerol. *ChemSusChem* **2020**, *13*, 2007–2011. [CrossRef]

129. Wang, Y.; Furukawa, S.; Song, S.; He, Q.; Asakura, H.; Yan, N. Catalytic Production of Alanine from Waste Glycerol. *Angew. Chem. Int. Ed.* **2020**, *59*, 2289–2293. [CrossRef] [PubMed]
130. Du, F.; Jin, X.; Yan, W.; Zhao, M.; Thapa, P.S.; Chaudhari, R.V. Catalytic H₂ Auto Transfer Amination of Polyols to Alkyl Amines in One Pot Using Supported Ru Catalysts. *Catal. Today* **2018**, *302*, 227–232. [CrossRef]

131. Jia, L.; Makha, M.; Du, C.-X.; Quan, Z.-J.; Wang, X.-C.; Li, Y. Direct Hydroxyethylation of Amines by Carbohydrates via Ruthenium Catalysis. *Green Chem.* **2019**, *21*, 3127–3132. [CrossRef]

132. Said Stålsmeden, A.; Belmonte Vázquez, J.L.; van Weerdenburg, K.; Rae, R.; Norrby, P.-O.; Kann, N. Glycerol Upgrading via Hydrogen Borrowing: Direct Ruthenium-Catalyzed Amination of the Glycerol Derivative Solketal. *ACS Sustain. Chem. Eng.* **2016**, *4*, 5730–5736. [CrossRef]

133. Kawahara, R.; Fujita, K.; Yamaguchi, R. Multialkylation of Aqueous Ammonia with Alcohols Catalyzed by Water-Soluble Cp\*Ir–Ammine Complexes. *J. Am. Chem. Soc.* **2010**, *132*, 15108–15111. [CrossRef] [PubMed]

134. Xu, Q.-S.; Li, C.; Xu, Y.; Xu, D.; Shen, M.-H.; Xu, H.-D. Ruthenium Catalyzed Amination Cyclization of 1,2,4-Butanetriol with Primary Amines: A Borrowing Hydrogen Strategy for 3-Pyrrolidinol Synthesis. *Chin. Chem. Lett.* **2020**, *31*, 103–106. [CrossRef]

135. Cumpstey, I.; Agrawal, S.; Eszter Borbas, K.; Martín-Matute, B. Iridium-Catalysed Condensation of Alcohols and Amines as a Method for Aminosugar Synthesis. *Chem. Commun.* **2011**, *47*, 7827–7829. [CrossRef]

136. Kort, M.J. Reactions of Free Sugars with Aqueous Ammonia. In *Advances in Carbohydrate Chemistry and Biochemistry*; Tipson, R.S., Horton, D., Eds.; Academic Press: New York, NY, USA; London, UK, 1970; Volume 25, pp. 311–349.

137. Shibamoto, T.; Bernhard, R.A. Investigation of Pyrazine Formation Pathways in Sugar-Ammonia Model Systems. *J. Agric. Food Chem.* **1977**, *25*, 609–614. [CrossRef]

138. Milić, B.L.; Piletić, M.V. The Mechanism of Pyrrole, Pyrazine and Pyridine Formation in Non-Enzymic Browning Reaction. *Food Chem.* **1984**, *13*, 165–180. [CrossRef]

139. Lichtenthaler, F.W. Unsaturated O- and N-Heterocycles from Carbohydrate Feedstocks. *Acc. Chem. Res.* **2002**, *35*, 728–737. [CrossRef]

140. Chen, X.; Yang, H.; Hülsey, M.J.; Yan, N. One-Step Synthesis of N-Heterocyclic Compounds from Carbohydrates over Tungsten-Based Catalysts. *ACS Sustain. Chem. Eng.* **2017**, *5*, 11096–11104. [CrossRef]

141. Yu, F.; Darcel, C.; Fischmeister, C. Single-Step Sustainable Production of Hydroxy-Functionalized 2-Imidazolines from Carbohydrates. *ChemSusChem* **2022**, *15*, e202102361. [CrossRef] [PubMed]

142. Pelckmans, M.; Mihaylov, T.; Faveere, W.; Poissonnier, J.; Van Waes, F.; Moonen, K.; Marin, G.B.; Thybaut, J.W.; Pierloot, K.; Sels, B.F. Catalytic Reductive Aminolysis of Reducing Sugars: Elucidation of Reaction Mechanism. *ACS Catal.* **2018**, *8*, 4201–4212. [CrossRef]

143. Pelckmans, M.; Vermandel, W.; Van Waes, F.; Moonen, K.; Sels, B.F. Low-Temperature Reductive Aminolysis of Carbohydrates to Diamines and Aminoalcohols by Heterogeneous Catalysis. *Angew. Chem. Int. Ed.* **2017**, *56*, 14540–14544. [CrossRef] [PubMed]

144. Kwok, T.; Hoff, O.; Armstrong, R.J.; Donohoe, T.J. Control of Absolute Stereochemistry in Transition-Metal-Catalysed Hydrogen-Borrowing Reactions. *Chem.–Eur. J.* **2020**, *26*, 12912–12926. [CrossRef]