bluuebunny/crossref_metadata_2025 huggingface dataset:
Manganese and Rhenium Tricarbonyl Complexes Equipped with Proton Relays in the Electrochemical CO2 Reduction Reaction
Authors: Mukherjee Jyotima , Siewert Inke
Published: January 2021

The minireview focuses on the electrochemical CO2 reduction catalysed by manganese and rhenium tricarbonyl complexes with α‐diimine ligands having pendant proton relays attached to the α‐diimine ligand. Since the pioneering work on [Re(CO)3(Lbpy)Cl], 1Cl, as molecular electrocatalyst in the CO2 reduction reaction in the 80's, some effort has been made to understand the mechanism of the catalytic cycle and to improve the efficiency of the conversion (Lbpy = 2,2'‐bipyrdine). Later it was shown that the corresponding Mn complex, [Mn(CO)3(Lbpy)Br], 2Br, is also active in the CO2‐to‐CO conversion. As the 2 electrons reduction of CO2 is coupled to the transfer of 2 protons, pendent proton relays have been introduced in the ligand framework with the aim to improve the proton management during catalysis, to stabilize intermediates, and to alter the redox and the pH‐dependent properties of the catalyst. We summarise in this review the outcome of these studies on the performance of the catalyst, in particular, with regard to the position of the proton relay and thus, its influence on the electronic structure, the reaction steps, and the kinetics.
Nanoparticles of Molecular Conductors and Superconductors: Progress Over the Last Ten Years
Authors: Jacob Kane , de Caro Dominique , Faulmann Christophe , Valade Lydie
Published: January 2021

We review conditions for growing molecular conductors and superconductors as nanoparticles, an attractive morphology for integrating them into electronic components or composite materials. Although the one‐dimensional character of these materials does not favor their growth as spheroidal objects, by adding growth controlling molecules to the reaction mixture, we succeeded in growing particles from 2 to 50 nm in size for fourteen systems. The choice of the growth controller depends on the nature of the chemical interactions it can establish with the reactive species to limit growth, and on the chemical or electrochemical synthesis procedure. We show that the chemical nature of the nanoparticles is alike single crystals. Due to resistive boundaries, conducting properties of nanoparticle powders are alike microcrystalline powders. Nevertheless, superconductivity occurs in three of the studied materials. The potential application of these nanomaterials is reported in four fields: composite materials, field‐effect transistors, thermoelectric components and biomedical materials.
Structural Diversity of Alkaline Earth Centered Gold(I) Metallacoronates
Authors: Sucena Suelen Ferreira , Pham Thu Thuy , Hagenbach Adelheid , Pham Chien Thang , Abram Ulrich
Published: January 2021

One‐pot reactions of the catechol‐scaffolding aroylbis(N,N‐diethylthiourea) H2Lcat with mixtures of alkaline earth nitrates M(NO3)2 (M2+ = Ca2+, Sr2+ or Ba2+) and (NEt4)[AuCl4] or [Au(tht)Cl] (tht = tetrahydrothiophene) in methanol in the presence of Et3N as supporting base give rise to neutral trinuclear gold(I) {2}‐metallacoronates with the composition of {M ⊂ [Au2(Lcat)2]} (1). Similar reactions with the pyridine‐centered aroylbis(N,N‐diethylthiourea) H2Lpy, however, produce complexes with the same metal‐to‐ligand ratio but with higher nuclearity {2M ⊂ [Au4(Lpy)4]} (2). In both 1 and 2, Au(I) ions are exclusively S‐bonded with the organic ligands and adopt a virtually linear coordination fashion. Such metal‐ligand binding is responsible for the formation of metallacoronands, which accommodate alkaline earth metal ions in their molecular voids, thereby resulting in host–guest coordination assemblies. The level of metal‐ligand aggregation in the resulting assemblies is dependent on the denticity, size and flexibility of the centered building block of the aroylbis(N,N‐diethylthiourea) ligands.
PdII(P‐P) Derivatives of o‐Quinone Annulated with Dithiete Cycle: Electrochemical Properties and Coordination Regioisomerism
Authors: Martyanov Konstantin A. , Abakumov Gleb A. , Baranov Evgeny V. , Khrizanforova Vera V. , Khrizanforov Mikhail N. , Kholin Kirill V. , Budnikova Yulia H. , Kuropatov Viacheslav A. , Cherkasov Vladimir K.
Published: January 2021

Regioselectivity in interaction of bifunctional o‐quinone annulated with dithiete cycle with tris(dibenzylideneacetone)dipalladium (Pd2dba3) in presence of bidentate phosphines was studied. Excluding the case of 1,2‐bis(diphenylphosphino)ethane (dppe) species, the formation of corresponding dithiolates with high yields was observed. Coordination of palladium to the dithiolene site of bifunctional ligand causes a distortion of the dioxolene site as well as significant decrease of its electron‐acceptor ability. The formation of both catecholate and dithiolate isomers, observed in case of reaction with dppe, might be interpreted as a consequence of kinetic factors.
Oxidative Addition of Biphenylene and Chlorobenzene to a Rh(CNC) Complex
Authors: Kynman Amy E. , Lau Samantha , Dowd Sean O. , Krämer Tobias , Chaplin Adrian B.
Published: January 2021

The synthesis and organometallic chemistry of rhodium(I) complex [Rh(CNC–Me)(SOMe2)][BArF4], featuring NHC‐based pincer and labile dimethyl sulfoxide ligands, is reported. This complex reacts with biphenylene and chlorobenzene to afford products resulting from selective C–C and C–Cl bond activation, [Rh(CNC–Me)(2,2'‐biphenyl)(OSMe2)][BArF4] and [Rh(CNC–Me)(Ph)Cl(OSMe2)][BArF4], respectively. A detailed DFT‐based computational analysis indicates that C–H bond oxidative addition of these substrates is kinetically competitive, but in all cases endergonic: contrasting the large thermodynamic driving force calculated for insertion of the metal into the C–C and C–Cl bonds, respectively. Under equivalent conditions the substrates are not activated by the phosphine‐based pincer complex [Rh(PNP‐iPr)(SOMe2)][BArF4].
Iron and Silver Complexes of 4‐(Imidazol‐1‐yl)‐2,6‐di(pyrazol‐1‐yl)‐pyridine (L), Including a [Fe3(µ‐F)2F6L8]+ Assembly
Authors: Capel Berdiell Izar , Kulmaczewski Rafal , Warriner Stuart L. , Cespedes Oscar , Halcrow Malcolm A.
Published: January 2021

Treatment of 2,4,6‐trifluoropyridine with sodium imidazolate, then 2 equiv. sodium pyrazolate, in two reaction steps yields the title ligand L in 40 % overall yield. Crystalline [FeL2][BF4]2 and [FeL2][ClO4]2 are isostructural high‐spin complexes, with highly twisted six‐coordinate geometries and pendant imidazolyl groups. Conversely, [Ag(µ‐L)]BF4·0.5MeCN is a linear coordination polymer of distorted square planar silver ions linked by κ1:κ3,µ‐L ligands. Some samples of [FeL2][BF4]2 were contaminated by [FeIII3(µ‐F)2F6L8]BF4, which was prepared in pure form following reaction of Fe[BF4]2·6H2O, Na3[FeF6] and L in appropriate ratios. The linear [{trans‐FeFL4}2(µ‐F)2FeF4]+ assembly is supported by monodentate L ligands coordinated through their imidazolyl donors, and donating C–H····F interactions to the central [FeF6]3– moiety. The cluster exhibits moderate antiferromagnetic coupling between its iron(III) centres.
Synthesis and Molecular Structure of Pseudo‐Hexacoordinated Pnictines Bearing 2‐Phenylpyridine Ligands
Authors: Sakabe Masato , Ooizumi Akihisa , Fujita Wataru , Aoyagi Shinobu , Sato Soichi
Published: January 2021

The pseudo‐hexacoordinated organo‐pnictogen(III) compounds tris[2‐(2‐pyridyl)phenyl]stibine [(ppy)3Sb,1] and tris[2‐(2‐pyridyl)phenyl]bismuthine [(ppy)3Bi,2], which bear three 2‐phenylpyridine (ppy) ligands, were prepared and isolated from the reaction of 2‐(2‐lithiophenyl)pyridine with the corresponding pnictogen(III) chloride (PnCl3; Pn = Sb, Bi). Compounds1and2were characterized using NMR spectroscopy, mass spectrometry, and elemental analysis. Their solid‐state structures were determined using single‐crystal X‐ray diffraction analysis, which revealed similar pseudo‐hexacoordinated, distortedfacialoctahedral bonding geometries around the central pnictogen atoms, wherein the three pyridyl groups coordinate to the pnictogen atoms via three weak LP(N)→σ*(Pn–C) donor–acceptor interactions. Natural bond orbital (NBO) and atoms in molecules (AIM) analyses were used to characterize the weak ionic interactions between the nitrogen and pnictogen atoms. The HOMOs of1and2correspond to the lone pairs of electrons on the central pnictogen atom, which indicates that these compounds can be classified as 14–Pn–6 chemical species.
Unexpected Supremacy of Non‐Dysprosium Single‐Ion Magnets within a Series of Isomorphic Lanthanide Cyanocobaltate(III) Complexes
Authors: Babeshkin Konstantin A. , Gavrikov Andrey V. , Petrosyants Svetlana P. , Ilyukhin Andrey B. , Belova Ekaterina V. , Efimov Nikolay N.
Published: January 2021

Slow relaxation of magnetization has been studied for a series of stable isomorphic 3D‐polynuclear Ln‐Co complexes comprising hexadentate [Co(CN)6]3– linkers, namely {[Ln(H2O)2][Co(CN)6]·2H2O}n where Ln = Tb (1), Dy (2), Er (3) and Yb (4). While 1 and 4 behave as field‐induced single‐ion magnets (SIMs), compounds 2 and 3 undergo rapid demagnetization even under magnetic fields up to 5000 Oe. The effective anisotropic energy barrier of 4 was estimated as 63 K (5000 Oe) which, to the best of our knowledge, is the highest value among Yb‐based SIMs. The obtained data are discussed in scope of the configuration of the Ln environment, i.e. accounting its composition and geometry as well as mutual arrangement of chemically unequal donating centers. Thus, the studied series of complexes represents very rare case when SIM performance of non‐dysprosium complexes far surpasses that of isomorphic Dy derivative.
Propene Hydroformylation Reaction Catalyzed by HRh(CO)(BISBI): A Thermodynamic and Kinetic Analysis of the Full Catalytic Cycle
Authors: Neto Daniel H. Cruz , Dos Santos Artur A. M. , Da Silva Júlio C. S. , Rocha Willian R. , Dias Roberta P.
Published: January 2021

In this article, full quantum mechanical calculations at the DFT‐D level were carried out to study the full catalytic cycle for the hydroformylation of propene, catalyzed by the [HRh(CO)(BISBI)] catalyst. All intermediates and transition states along the elementary steps of the whole catalytic cycle were located and properly characterized. The kinetic constants calculated from transition state theory together with the application of the steady‐state approximation were used to build a kinetic model for the hydroformylation reaction. The calculations show that regioselectivity of the reaction is set at the olefin insertion step, with the H2oxidative addition being the rate‐determining step of the entire cycle, with an activation energy of 26.0 kcal.mol‐1for the linear pathway. The kinetic model showed that the CO gas acts as an inhibitor of the reaction at high pressure, and depending on the CO partial pressure, the rate of linear product formation is around 4 to 10 times faster. In line with experimental observations, our computational kinetic model indicated that at high CO partial pressures (> 40 atm), the HRh(CO)(BISBI) catalyst decreases its selectivity. Also was predicted from the computational kinetic model, that the reaction rates for both productions of normal and iso‐butanal are less sensitive to effects of H2partial pressure concerning the observed with the variation of the partial pressure of CO gas.
Optimizing Photoluminescence Quantum Yields in Uranyl Dicarboxylate Complexes: Further Investigations of 2,5‐, 2,6‐ and 3,5‐Pyridinedicarboxylates and 2,3‐Pyrazinedicarboxylate
Authors: Thuéry Pierre , Atoini Youssef , Kusumoto Sotaro , Hayami Shinya , Kim Yang , Harrowfield Jack
Published: January 2021

The 2,5‐, 2,6‐, and 3,5‐pyridinedicarboxylic (2,5‐, 2,6‐ and 3,5‐pydcH2), and 2,3‐pyrazinedicarboxylic (2,3‐pyzdcH2) acids have been used to synthesize six uranyl ion complexes including various counterions under solvo‐hydrothermal conditions. While [NH4]2[UO2(2,6‐pydc)2]·3H2O (1) is a discrete, mononuclear species, [UO2(2,6‐pydc)2Cu(R,S‐Me6cyclam)] (2) crystallizes as a monoperiodic coordination polymer through axial bonding of copper(II) to carboxylate donors. [PPh3Me][UO2(OH)(2,5‐pydc)]·H2O (3) and [Ni(R,S‐Me6cyclam)][UO2(OH)(2,5‐pydc)]2·2H2O (4) contain di‐hydroxo‐bridged dinuclear uranyl subunits assembled into homometallic, monoperiodic polymers. [(UO2)2(3,5‐pydc)2(HCOO)2Ni(R,S‐Me6cyclam)] (5) crystallizes as a heterometallic diperiodic network with the V2O5 topology, and [PPh4][UO2(OH)(2,3‐pyzdc)] (6) is a diperiodic species with sql topology. All complexes have well‐resolved uranyl emission spectra in the solid state, and three of them have photoluminescence quantum yields among the highest reported for uranyl carboxylate complexes, 44 % for 1, 71 % for 3, and 36 % for 6.
Tetrafluoroaryl Phosphonic Acid Functionalized Polyphosphazenes – Synthesis, Characterization, and Evaluation of Proton Conductivity
Authors: Alter Christian , Wiesemann Markus , Neumann Beate , Stammler Hans‐Georg , Hoge Berthold
Published: January 2021

A convergent approach for the incorporation of tetrafluoroaryl phosphonate moieties into cyclic triphosphazenes and linear phosphazene resins is described. Our high yield procedure is based on the treatment of chlorinated poly‐ and cyclotriphosphazenes with p‐HO(C6F4)P(O)(OR)2 (R = Me, Et) in the presence of potassium carbonate. Characterization of the modified cyclotriphosphazenes was accomplished by NMR and IR spectroscopy as well as by mass spectrometry. Similarly, a phosphazene resin decorated with phosphonic esters is characterized by NMR and IR spectra and GPC. Exchange of the ethyl group by a trimethylsilyl group in the novel phosphazene derivatives was effected by the reaction with trimethylsilyl bromide. The resulting silyl phosphonates were converted into the corresponding phosphonic acids by exposure to an excess of methanol. Proton conductivities of the novel phosphonic acid derivatives of poly‐ and cyclotriphosphazenes were studied by electrochemical impedance spectroscopy under anhydrous conditions.
Halogenation of Diorganotelluride [2,6‐(Me2NCH2)2C6H3]TenBu: Synthesis, Molecular and Electronic Structural Investigation of Monoorgano Dihalotelluronium(IV) Cation
Authors: Deka Rajesh , Gupta Anand , Sarkar Arup , Butcher Ray J. , Singh Harkesh B.
Published: January 2021

A simple methodology for the synthesis of heteroleptic diorganotelluride [2,6‐(Me2NCH2)2C6H3]TenBu (1) and homoleptic diorganotelluride [2,6‐(Me2NCH2)2C6H3]2Te (2) is reported. The halogenation reactions of diorganotelluride 1 are studied. In particular, the reaction of 1 with Br2 resulted in the isolation of a monoorgano dibromotelluronium(IV) cation, namely [2,6‐(Me2NCH2)2C6H3TeBr2]·Br3 ([3]·Br3). The reaction of [3]·Br3 with K2PdCl4 afforded a monoorgano mixed dihalotelluronium(IV) cation, [2,6‐(Me2NCH2)2C6H3TeClBr]·PdBr4 ([4]·PdBr4). When diorganotelluride 1 was treated with I2, the reaction afforded the tellurenium(II) cation, [2,6‐(Me2NCH2)2C6H3Te]·I2·I3 ([5]·I2·I3). The reaction of 1 with HgCl2 resulted in the isolation of dimeric diorganoditelluroxonium(IV) cation, [2,6‐(Me2NCH2)2C6H3Te(µ‐O)]2·Hg2Cl6 ([6]·Hg2Cl6). A similar diorganoditelluroxonium(IV) cation, namely [2,6‐(Me2NCH2)2C6H3Te(µ‐O)]2·2Br ([6]·2Br) was also obtained by the reaction of 1 with Br2 and NaOH. The crystallographic studies suggest that for each compound, both the N atoms from the pendant arms make strong Intramolecular Chalcogen Bonding (IChB) interactions with the Te center(s). The presence of a strong N→Te IChB interaction in the synthesized compounds was further validated by DFT calculations.
Molecular Systems Combining Porphyrinoids and N‐Heterocyclic Carbenes
Authors: Longevial Jean‐François , Rose Clémence , Poyac Ludivine , Clément Sébastien , Richeter Sébastien
Published: January 2021

Porphyrins and N‐heterocyclic carbenes (NHCs) are both relevant ligands in the fields of coordination and organometallic chemistry. Despite evident structural differences, porphyrins and NHCs have a lot in common such as their ability to form strong metal‐ligand bonds and their use in catalysis, materials science and biomedicine. During the last decade, several molecular systems combining porphyrins and NHC ligands were reported in the literature. The present review gathers relevant examples where NHC ligands are either axially bonded to metalloporphyrins or covalently attached to the porphyrin cores. Structural diversity, electronic interplay between porphyrins and NHCs and some relevant applications in catalysis and biomedicine are notably described. Finally, molecular systems combining NHCs with other original porphyrinoids such as N‐confused porphyrins, subporphyrins and norcorroles are also presented.
Comment on “Detection of the Elusive Nitrogen‐Centered Radicals from Catalytic Hofmann–Löffler Reactions”
Authors: Korth Hans‐Gert
Published: January 2021

Missing β‐hydrogen hyperfine splittings and inconsistent g‐factors reveal that the proposed sulfamidyl radical has not been detected by EPR spectroscopy on photolysis of N‐halogenated sulfonamides. Rather, nitroxide radicals formed via side reactions have been observed.
Azidative Aromatization of Quinone Methides Under Transition Metal and Solvent Free Conditions
Authors: Xiu Haiping , Li Tingting , Song Chun , Ma Yudao
Published: January 2021

Organic azides are synthetically and commercially useful intermediates with a wide variety of applications. In this work, azidative aromatization of quinone methides under transition metal and acid‐free conditions can avoid the forming of highly toxic and explosive hydrazoic acid and azide salts. The use of cesium carbonate as a catalyst and water as an effective additive, elimination of a transition metal catalyst, reaction solvent, and column chromatography separation led to an overall greener approach to access valuable benzyl azides in quantitative yields. Because the procedure can be used to prepare a serious of benzyl azides without contamination by any harmful transition metal residues, this new method has great potential in pharmaceutical synthesis and chemical biology studies.
Silver/Palladium Relay Catalyzed Cross‐Coupling of N'‐Acetyl‐8‐quinolinesulfonylhydrazide with Alcohols: An Easy Access to 8‐Quinolinesulfinate Esters
Authors: Yadav Anamika , Ambule Mayur D. , Kant Ruchir , Srivastava Ajay K.
Published: January 2021

An efficient strategy for the synthesis of unexplored 8‐quinolinesulfinate esters has been reported. The method involves in situ generation of quinoline sulfinate from N'‐acetylquinoline‐8‐sulfonohydrazide via silver mediated cleavage followed by palladium‐catalyzed cross‐coupling with 1° and 2° alcohols to yield sulfinate esters. A variety of substituted alcohols were successfully employed in the reaction. Control experiments performed to understand the mechanism, revealed that the transformation follows a radical pathway and the alcohol oxygen get incorporated in the resulting sulfinate esters. Two of the chirally pure alcohols were also used in the transformation to study the diastereoselectivity in the reaction. In order to demonstrate the synthetic utility, a representative allyl‐quinoline‐8‐sulfinate 3f was successfully converted into the 8‐(allylsulfonyl)‐quinoline 4 via palladium(II) acetate mediated isomerization.
Regioselective Synthesis of Arylsulfonyl Benzophenones via Aerobic Oxidative [3+3] Benzannulation Reactions
Authors: Yadav Deepak , Joshi Prabhakar R. , Sharma Sunil K. , Menon Rajeev S.
Published: January 2021

Regioselective synthesis of 3‐arylsulfonyl benzophenone derivatives via base mediated, aerial‐oxidative [3+3] benzannulation of α,β‐unsaturated aldehydes and 4‐sulfonyl butenones is reported. A variety of readily available acyclic building blocks are transformed into substituted biaryl ketones in this benzannulation reaction. The reaction proceeds under mild conditions in an open flask and uses atmospheric oxygen as oxidant to afford good yields of the products. Analogous benzannulation reactions of chalcone afforded highly substituted m‐terphenyl‐benzophenone derivatives.
Efficient Synthesis of ω‐[18F]Fluoroaliphatic Carboxylic Esters and Acids for Positron Emission Tomography
Authors: Larkina Mariia S. , Ozerskaya Anastasia V. , Podrezova Ekaterina V. , Belousov Mikhail V. , Tolmachev Vladimir , Zhdankin Viktor V. , Yusubov Mekhman S.
Published: January 2021

[18F]Fluoroaliphatic carboxylic acids are important PET tracers that have demonstrated a considerable potential to address the fatty acid oxidation‐dependent processes in clinical patients. Herein, we report an efficient radiosynthetic approach to ω‐[18F]fluoroaliphatic carboxylic esters and acids by nucleophilic radiofluorination of the readily available iodocarboxylic esters. Methyl 6‐[18F]fluorohexanoate was further applied as a starting material for the preparation of the succinimide ester (NHS ester)‐containing bifunctional radiofluorinated prosthetic group in two simple steps, 10 min each. The synthesized NHS ester of 6‐[18F]fluorohexanoic acid can serve as an important reagent for a quick and efficient conjugation with peptides or proteins via amino groups of lysines.
Synthesis of Pyridazin‐3(2H)‐one Derivatives by the Reaction of CH‐Acids with Dichlorodiazadienes
Authors: Sergeev Pavel G. , Khrustalev Victor N. , Nenajdenko Valentine G.
Published: January 2021

The reactions of 4,4‐dichloro‐1,2‐diazabuta‐1,3‐dienes with dimethyl malonate, cyanoacetic esters and ethyl acetoacetate provided straightforward access to highly functionalized pyridazine derivatives. The approach was found to be very general for the highly efficient synthesis of various pyridazine derivatives which can be isolated in moderate to excellent yields. The possibility of their subsequent functionalization was demonstrated. Moreover, the absorption characteristics in the UV/Vis‐range and luminescence were studied for all synthesized compounds.
Facile Synthesis of γ‐Ketonitriles in Water via C(sp2)–H Activation of Aromatic Aldehydes over Cu@g‐C3N4 under Visible‐Light
Authors: Rai Vijai K. , Verma Fooleswar , Bhardiya Smita R. , Sheshma Harendra , Rai Ankita , Singh Manorama
Published: January 2021

A facile C(sp2)–H activation of aldehyde under visible‐light conditions using Cu@g‐C3N4 as photocatalyst and water as solvent is reported. The envisaged method involves photocatalytic intermolecular Stetter reaction using differently substituted aldehydes and acrylonitrile to produce various γ‐keto nitriles in good to excellent yield (80–95 %) and 4–10 h at r.t. Operational simplicity, ambient reaction conditions, visible‐light condition, and application of the Cu@g‐C3N4 as photocatalyst make the envisaged protocol an efficient and highly green alternative to the existing methods for synthesis of γ‐keto nitriles.
Imino‐λ3‐iodane and Catalytic Amount of I2‐Mediated Synthesis ofN‐Allylsulfenamides via [2,3]‐Sigmatropic Rearrangement
Authors: Makitalo Cody L. , Yoshimura Akira , Rohde Gregory T. , Mironova Irina A. , Yusubova Rosa Y. , Yusubov Mekhman S. , Zhdankin Viktor V. , Saito Akio
Published: January 2021

A facile metal‐free [2,3]‐sigmatropic rearrangement reaction of allyl sulfides viaN‐sulfilimine intermediates has been developed. Treatment of allyl sulfides with imino‐λ3‐iodanes in the presence of a catalytic amount of elemental iodine allowed the reaction to proceed under mild conditions and gave the correspondingN‐allylsulfenamide compounds in moderate to good yields. SeveralN‐allylsulfenamide structures have been confirmed by single‐crystal X‐ray crystallography. The reaction initially involves the sulfonylimino group transfer reaction between imino‐λ3‐iodane and the sulfur atom, resulting in the formation ofN‐sulfilimine species, followed by [2,3]‐sigmatropic rearrangement to form theN‐allylsulfenamide.
Regioselective Synthesis of Halotriazoles and their Utility in Metal Catalyzed Coupling Reactions
Authors: Gharpure Santosh J. , Naveen Sudi , Chavan Rupali S. , Padmaja
Published: January 2021

Synthesis of halotriazoles has been studied in the past few decades. Today, coupling reactions such as Heck, Suzuki, Sonogashira, and Stille are important tools in organic synthesis for the construction of C–C bonds. While these coupling reactions have been well utilized with simple haloarenes or halo‐olefins, now they are fast emerging on halotriazoles as well. This review summarizes the development of coupling reactions on halotriazoles, some of which are also biological relevant.
Consecutive Oxidation/Condensation/Cyclization/Aromatization Sequences Catalyzed by Nanostructured Iron(III)‐Porphyrin Complex towards Benzoxazole Derivatives
Authors: Aboonajmi Jasem , Sharghi Hashem , Aberi Mahdi , Shiri Pezhman
Published: January 2021

A facile, efficient, and eco‐friendly strategy to access benzoxazole heterocyclic products has been accomplished through oxidation of catechols followed by condensation/cyclization/aromatization sequences. This process is catalyzed by nanostructured iron(III)‐porphyrin complex to form desired benzoxazole derivatives at room temperature under air condition. The procedure is widely applicable to diverse amines, and can provide the heterocyclic products in a scalable fashion, as well. One of the most significant types of oxidizing agents in nature is the iron‐porphyrin complexes (0.1 mol‐%), existing in the structure of hemoglobin. They have benefits such as low toxicity and high oxidation potential for many substrates.
Synthesis and Properties of Dibenzo[a,j]acridines
Authors: Ammon Erich , Ohlendorf Lars , Villinger Alexander , Ehlers Peter , Langer Peter
Published: January 2021

A convenient three‐step synthesis of dibenzo[a,j]acridines is reported which relies on regioselective Pd‐catalyzed cross‐coupling reactions of 2,3,5,6‐tetrachloropyridine and subsequent Brønsted acid mediated cycloisomerization. Products are obtained in good yields and the method is broadly applicable. For selected dibenzo[a,j]acridines, photophysical and electrochemical properties were studied.
Metal‐Free Alkenylation of Salicylaldehydes with Boronic Acids: Synthesis of Skipped Dienes and 2H‐Chromenes
Authors: Harris Dylan H. , Barichello Renata O. , Bolshan Yuri
Published: January 2021

Metal‐free alkenylation of salicylaldehydes and the preparation of 2H‐chromenes have been developed. Reactions occur in the presence of tetrafluoroboric acid diethyl ether complex. Vinylboronic acid derivatives including indeneboronic acid react readily with salicylaldehydes to afford the corresponding skipped dienes. When 6‐bromo or 6‐chlorosalicylaldehydes are submitted to the reaction conditions the formation of 2H‐chromenes is observed in good to excellent yields.
Evidence for “Halogen‐Dance” and Ring‐Exchange Reactions in Chloro‐methylthio‐ferrocenes
Authors: Blockhaus Tobias , Bernhartzeder Stefanie , Kempinger Werner , Klein‐Heßling Christian , Weigand Stefan , Sünkel Karlheinz
Published: January 2021

The pentachloroferrocenes [C5Cl5]Fe[C5H4X] (X = H, Br, SMe) react with LiTMP and MeSSMe to form mixtures of compounds, that contain besides the expected products of deprotonation also one or more complexes with a [C5Cl4(SMe)] ligand. This latter observation makes the otherwise rarely observed occurrence of “halogen dance reactions” in chloroaromatics very probable. 1,2,3‐Trichloroferrocene yields with BuLi and MeSSMe products of both halogen‐metal‐exchange and of deprotonation. Additionally, in all examined systems, the observation of some highly‐substituted complexes with eight or more substituents hints to the involvement of cyclopentadienyl exchange reactions, which has also rarely been observed under such mild conditions. The molecular structures of [C5Cl4(SMe)]Fe[C5H3BrX] (X = SMe or SOMe), [C5Cl4(SMe)]Fe[C5H2Cl(SMe)2], [C5Cl2(SMe)3]2Fe, and [C5HCl3(SMe)]2Fe have been determined by X‐ray diffraction.
Amino Acid‐Based Dithiocarbamates as Efficient Intermediates for Diversity‐Oriented Synthesis of Thiazoles
Authors: Ziyaei Halimehjani Azim , Khalesi Maryam , Breit Bernhard
Published: January 2021

Amino acid‐based dithiocarbamates were introduced as efficient intermediates for the synthesis of a diverse library of novel di‐ and tri‐substituted thiazoles via condensation with various reagents such as anhydrides, acyl halides, benzene sulfonyl chloride, trifluoromethanesulfonic anhydride, chloroethyl formate, and diethyl chlorophosphate. The utilities of adducts in further organic synthesis were confirmed by Sonogashira and oxidation reactions. In addition, reaction of aspartic acid‐based dithiocarbamates with anhydrides affords the corresponding fused 6,6a‐dihydrofuro[3,2‐d]thiazol‐5(3aH)‐ones diastereoselectively in excellent yields.
Metal‐Free Electrochemical Coupling of Vinyl Azides: Synthesis of Phenanthridines and β‐Ketosulfones
Authors: Li Guodong , Kong Xianqiang , Liang Qi , Lin Long , Yu Ke , Xu Bo , Chen Qianjin
Published: January 2021

We reported an efficient and environmentally benign electrochemical synthesis of phenanthridines by oxidative coupling of vinyl azides with sodium azide or benzenesulfonyl hydrazides, for the first time. The reaction conditions are mild, and no additional metal‐catalyst or exogenous oxidants are needed. The protocol has broad substrate scope and high functional group tolerance. Furthermore, this green electrochemical procedure can be readily extended to the synthesis of β‐ketosulfones. Gram scale reactions further demonstrate the practicability.
Metal‐Free Electrochemical Oxidative Dihalogenation of Quinolines on the C5 and C7 Positions Using N‐Halosuccinimides
Authors: Hou Jiahao , Wang Kai , Zhang Changjun , Wei Tingting , Bai Renren , Xie Yuanyuan
Published: January 2021

An efficient and convenient method for electrochemically oxidative dichlorination or dibromination of 8‐aminoquinolines on C5 and C7 positions using N‐halosuccinimides (NCS and NBS) as the halogen source was described. Substrates with various functional groups were transformed smoothly and the halogenated products were obtained in good to excellent yields. These transformations feature transition‐metal‐free, oxidant‐free, and short reaction time.
Synthesis of Cycloheptatrienes, Oxepines, Thiepines, and Silepines: A Comparison between Brønsted Acid and Au‐Catalysis
Authors: Sprenger Kristin , Golz Christopher , Alcarazo Manuel
Published: January 2021

The cyclization of 1‐(benzyl‐, oxyaryl‐, thioaryl‐, and silaaryl)‐2‐ethynylbenzenes under Brønsted acid‐ and Au(I)‐catalysis is described. Brønsted acid catalysis favors without exception the formation of the products derived from the regioselective protonation of the alkyne to generate the most stable vinyl carbocation intermediate. This determines the type of cyclization following this initial step and therefore, the structure of the products. Contrarily, with only a few exceptions, for example, when the substrate contains a terminal alkyne moiety, Au‐catalysis preferentially promotes the formation of seven‐membered rings via 7‐endo‐dig cyclization. This reaction pathway is imposed even if a priori the natural electronic polarization in the substrates would suggest another operating mechanism. Making use of these reactivity patterns, a series of structurally differentiated dibenzo‐cycloheptatrienes, ‐oxepines, ‐thiepines and ‐silepines have been synthesized with excellent yields and regioselectivities.
Desymmetrization Strategy to Achieve Triptycene‐Based 3,6‐Dimethoxytriphenylenes via Oxidative Cyclodehydrogenation
Authors: Reinhard Dennis , Rominger Frank , Mastalerz Michael
Published: January 2021

A desymmetrization strategy has been developed to achieve a triptycene‐based hexamethoxy tris triphenylene in high yields by taking into account the regioselectivity of the Scholl‐type oxidative cyclodehydrogenation governed by methoxy groups. Different routes starting from D3h‐ and C3v‐symmetric precursors have been compared as well as by Mallory‐type photocyclizations.
Synthesis of Seco‐Analogues of the DHCR24 Inhibitor SH‐42
Authors: Heerdegen Desirée , Reuter Doreen , Kornmayer Moritz M. , Kriegler Katharina N. , Müller Christoph , Mayer Peter , Bracher Franz
Published: January 2021

In a project aimed at the further development of the potent steroidal anti‐inflammatory Δ24‐dehydrocholesterol reductase (DHCR24) inhibitor SH‐42 we worked out routes to ring B seco‐steroidal analogues. The required building blocks, bearing rings C and D of the parent steroidal structure, were synthesised starting from ergocalciferol. The novel seco‐analogues carry aromatic residues as ring A equivalents at C‐4 position with variation of the linker length resulting in 4‐aryl‐, 4‐benzyl‐ and 4‐(arylethyl)perhydroindanes. As saturated analogues of the latter 4‐(cyclohexylethyl)perhydroindanes were prepared. Moreover, aromatic and aliphatic residues were attached to C‐5 position of the perhydroindane scaffold. Unfortunately, none of these structurally diverse seco‐analogues of SH‐42 showed noteworthy inhibition of target enzyme DHCR24, indicating the relevance of the intact steroidal structure for the development of potent inhibitors of this enzyme.
Synthesis of Novel Chiral Spiroisoxazolidine‐β‐Lactams from 6‐Alkylidenepenicillanates: A 1,3‐Dipolar Cycloaddition Approach
Authors: Alves Américo J. S. , Pinho e Melo Teresa M. V. D.
Published: January 2021

The synthesis of a library of 6‐alkylidene‐β‐lactams, derived from 6‐aminopenicillanic acid is reported. The 1,3‐dipolar cycloaddition of these 6‐alkylidenepenicillanates with nitrones was explored as an approach to synthesize novel chiral spiroisoxazolidine‐β‐lactams. Quantum chemical calculations, at the DFT level of theory, were carried out to elucidate the 3D structure of the synthesized compounds. The reported methodology, which involves the generation of three new consecutive stereogenic centers, proved to be regio‐ and stereoselective, leading to novel chiral spiroisoxazolidine‐penicillanates efficiently.
Response to Comment on “Detection of the Elusive Nitrogen‐Centered Radicals from Catalytic Hofmann–Löffler Reactions”
Authors: Bosnidou Alexandra E. , Duhamel Thomas , Muñiz Kilian
Published: January 2021

The initial steps of the catalytic Hofmann–Löffler reaction include the formation of the N‐halogenated amine with further formation of a nitrogen‐centered radical. We had reported the presence and detection of a radical through EPR spectroscopy. Based on new data, we discuss the observed EPR signal.
Conformational Lock of Glycosyl Donors Using Cyclic Carbamates
Authors: Villameriel Jaime Moyano , Pedersen Christian Marcus
Published: January 2021

Axial rich glycosyl donors often display superior reactivity and stereoselectivity in glycosylations. In this study, a glucosamine glycosyl donor, locked in a 1C4 conformation by a six‐membered carbamate ring, i.e. an oxazinone, is synthesized and studied. The 2N,4O carbamate is synthesized in one step from the corresponding azide. The glycosylation properties were studied by glycosylating different alcohols. Derivatives of the glycosyl donor were synthesized by introducing Ac, Troc, Ts, and Ms groups on the oxazinone nitrogen. The ring opening to give the glycoside in the 4C1 conformation was found to proceed smoothly using Zemplén conditions.
Divergent and Regioselective Synthesis of (Trifluoromethyl/carboxyethyl)benzo[4,5]imidazo[1,2‐a]pyrimidines from β‐Enamino Diketones
Authors: Andrade Valquiria P. , Mittersteiner Mateus , Bonacorso Helio G. , Martins Marcos A. P. , Zanatta Nilo
Published: January 2021

A divergent and regioselective cyclocondensation reaction of β‐enamino diketones with 2‐aminobenzimidazole is reported. The β‐enamino diketones react with 2‐aminobenzimidazole to form exclusively 1,2‐ or 1,4‐regioisomers of benzo[4,5]imidazo[1,2‐a]pyrimidines, depending on the nature of the EWG group in the diketones: when the diketone has a carboxyethyl group, only the 1,2‐regioisomer was obtained; and when the EWG = CF3, only the 1,4‐regioisomer was isolated. The structure of the obtained products was unambiguously determined by 2D‐NMR experiments and single‐crystal X‐ray analysis.
The Cyclization of Allenyl‐Substituted Hydroxylamines to 1,2‐Oxazines: an Experimental and Computational Study
Authors: Utecht‐Jarzyńska Greta , Jasiński Marcin , Würthwein Ernst‐Ulrich , Reissig Hans‐Ulrich
Published: January 2021

To gain a deeper understanding of the formation of the synthetically important 3,6‐dihydro‐2H‐1,2‐oxazines, the 6‐endo‐trig cyclization of allenyl‐substituted hydroxylamines was experimentally investigated in detail employing a model compound. The solvent effect was moderate with respect to the rate, but crucial to suppress side‐product formation. Surprisingly, acids or bases had no big influence on the cyclization rate. With O‐deuterated allenyl hydroxylamine a high primary isotope effect was found, indicating that the proton transfer is crucial in the rate‐determining step. DFT calculations evidence that the allenyl‐substituted hydroxylamine is converted into an energetically similar zwitterionic intermediate with an allyl cation subunit. It cyclizes to the 1,2‐oxazine as the most stable species. Alternative pathways starting from the zwitterion were computationally investigated. Interestingly, it can also undergo a fragmentation to give a pentadiene derivative and a nitroso compound. The hetero Diels–Alder reaction of these components may also deliver the 1,2‐oxazine. To evaluate an alternative mechanistic scenario, calculations of the protonated allenyl‐substituted hydroxylamine were also performed.
The Ugi Three‐Component Reaction; a Valuable Tool in Modern Organic Synthesis
Authors: Tripolitsiotis Nikolaos P. , Thomaidi Maria , Neochoritis Constantinos G.
Published: January 2021

The Ugi three component reaction (U‐3CR) is a variation of the famous Ugi reaction, discovered almost 60 years ago. Today it is somehow neglected, compared to the classical variation, although the α‐aminoamides, derived from this reaction, have been utilized as inhibitors for various targets and even commercial drugs, offering improved pharmacokinetic properties. In this review, we are describing the scope and limitations of the reaction with a special focus on the developed catalytic protocols, the bioactive compounds, and drugs which are based on the reaction and finally the post modifications that have been reported in order to access drug‐like and privileged scaffolds. A special focus is given to the 3D solid state conformations of the U‐3CR derivatives.
Synthesis of 3‐Unsubstituted Phthalides from Aryl Amides and Paraformaldehyde via Ruthenium(II)‐Catalyzed C–H Activation
Authors: Zhou Chao , Zhao Junqi , Chen Wenkun , Imerhasan Mukhtar , Wang Jun
Published: January 2021

A straightforward and convenient route has been developed for the synthesis of 3‐unsubstituted phthalide derivatives from aryl amides and paraformaldehyde by ruthenium(II)‐catalyzed C–H activation. The reaction proceeds through tandem ortho‐hydroxymethylation of aryl amide and subsequent intramolecular lactonization.
Synthesis of Constrained C‐Glycosyl Amino Acid Derivatives Involving 1,3‐Dipolar Cycloaddition of Cyclic Nitrone as Key Step
Authors: Rouzier Florian , Sillé Rosanne , Montiège Ophélie , Tessier Arnaud , Pipelier Muriel , Dujardin Gilles , Martel Arnaud , Nourry Arnaud , Guillarme Stéphane
Published: January 2021

An efficient two‐step strategy for the synthesis of constrained C‐glycosyl amino acid derivatives from C‐vinylglycosides involving a 1,3‐dipolar cycloaddition using l‐(–)‐menthone‐derived nitrone as the key step is described. After optimization of 1,3‐dipolar cycloaddition conditions, various C‐vinylglycosides were tested leading exclusively to one diastereoisomer of the corresponding cycloadduct in good to excellent yields. The total facial selectivity observed was also studied by DFT calculations. Original conformationally restricted C‐glycosyl amino acid derivatives (8 examples) were isolated after simple cleavage of the chiral auxiliary.
Synthesis and Structure of meso‐Substituted Dibenzihomoporphyrins
Authors: Grover Nitika , Emandi Ganapathi , Twamley Brendan , Khurana Bhavya , Sol Vincent , Senge Mathias O.
Published: January 2021

Bench‐stable meso‐substituted di(p/m‐benzi)homoporphyrins were synthesized through acid‐catalyzed condensation of dipyrrole derivatives with aryl aldehydes. The insertion of a 1,1,2,2‐tetraphenylethene (TPE) or but‐2‐ene‐2,3‐diyldibenzene unit in the porphyrin framework results in the formation of dibenzihomoporphyrins, merging the features of hydrocarbons and porphyrins. Single crystal X‐ray analyses established the non‐planar structure of these molecules, with the phenylene rings out of the mean plane, as defined by the dipyrromethene moiety and the two meso‐carbon atoms. Spectroscopic and structural investigations show that the macrocycles exhibit characteristics of both TPE or but‐2‐ene‐2,3‐diyldibenzene and dipyrromethene units indicating the non‐aromatic characteristics of the compounds synthesized. Additionally, the dibenzihomoporphyrins were found to generate singlet oxygen, potentially allowing their use as photosensitizers.
Efficient Synthesis of 2‐Amino‐1‐Arylethanols Through a Lewis Base‐Catalyzed SiCl4‐Mediated Asymmetric Passerini‐Type Reaction
Authors: Gernet Aurélie , Ratovelomanana‐Vidal Virginie , Pirat Jean‐Luc , Virieux David , Ayad Tahar
Published: January 2021

We herein report, a practical and efficient strategy for the synthesis of enantiomerically enriched 2‐amino‐1‐arylethanols, a structural motif commonly encountered in the family of β‐adrenergic blockers or agonists, through a Lewis base‐catalyzed SiCl4‐mediated asymmetric Passerini‐type reaction of isocyanides with aldehydes. The protocol features a simple one‐pot, two‐step procedure, the use of commercially available starting materials, a broad functional group tolerance, and high levels of selectivity up to 98.5:1.5 er. Application to the synthesis of the salbutamol acetate salt, a drug widely used as a bronchodilator to manage asthma and other chronic obstructive airway diseases is also reported.
Tetrabromomethane as an Organic Catalyst: a Kinetic Study of CBr4‐Catalyzed Schiff Condensation
Authors: Yunusova Sevilya N. , Bolotin Dmitrii S. , Vovk Mikhail A. , Tolstoy Peter M. , Kukushkin Vadim Yu.
Published: January 2021

Tetrabromomethane functions as an organic catalyst for non‐redox reactions of carbonyl species and, in particular, it enhances the aldehyde–acyl hydrazide condensation to give N‐acyl hydrazones. This simple, inexpensive, and commercially available halomethane provides up to 14‐fold acceleration of the Schiff reaction; the kinetic data indicate that the studied condensation exhibits the first order on CBr4. The catalytic activity of CBr4 is significantly higher than the activity of other halogen‐containing species, such as CHX3 or ArX (X = Cl, Br, I).
Gold(I)‐Catalyzed Allene–Diene–Alkyne Coupling Reaction to Polycycles
Authors: Semleit Nina , Kreuzahler Mathis , Haberhauer Gebhard
Published: January 2021

In general, the design of complex polycycles from simple building blocks is challenging and requires many reaction steps. Herein, we present that complex polycycles can be synthesized starting from two alkyne building blocks in a one‐pot reaction using gold(I) as catalyst, in yields up to 77 %. Mechanistically, the process can be described as cascade reaction in two steps: first, the allene is formed by gold(I)‐catalyzed dearomatization, second, the desired product is then obtained by allene–diene–alkyne coupling. Quantum chemical investigations confirm the assumed mechanism. In sum, five new C–C bonds are built in one sweep, which is extraordinary since non‐identical building blocks are combined in this reaction. The introduced new allene–diene–alkyne coupling reaction paves the way for several new syntheses of cycles and polycycles considering potential intermolecular reactions.
Catalytic Selective Oxidation of Primary and Secondary Alcohols Using Nonheme [Iron(III)(Pyridine‐Containing Ligand)] Complexes
Authors: Panza Nicola , di Biase Armando , Rizzato Silvia , Gallo Emma , Tseberlidis Giorgio , Caselli Alessandro
Published: January 2021

The selective oxidation of different primary and secondary alcohols to carbonyl compounds by hydrogen peroxide was found to be catalyzed in conversion ranging from good to excellent by an iron(III) complex of a pyridine‐containing macrocyclic ligand (Pc‐L), without the need of any additive. The choice of the counteranion (Cl, Br, OTf) appeared to be of fundamental importance and the best results in terms of selectivity (up to 99 %) and conversion (up to 98 %) were obtained using the well‐characterized [Fe(III)(Br)2(Pc‐L)]Br complex, 4c. Magnetic moments in solid‐state, also confirmed in solution ([D6]DMSO) by Evans NMR method, were calculated and point out to an iron metal center in the high spin state of 5/2. The crystal structure shows that the iron(III) center is coordinated by the four nitrogen atoms of the macrocycle and two bromide anions to form a distorted octahedral coordination environment. The catalytic oxidation of benzyl alcohol in acetonitrile was found occurring with better conversions and selectivities than in other solvents. The reaction proved to be quite general, tolerating aromatic and aliphatic alcohols, although very low yields were obtained for terminal aliphatic alcohols. Preliminary mechanistic studies are in agreement with a catalytic cycle promoted by a high‐spin iron complex.
Chemoselective Arylation of Dialkyl Diselenides and Application to the Synthesis of a ε‐N,N,N‐Trimethyllysine Derivative
Authors: Takahashi Ryuhei , Sakamoto Kenta , Umezawa Naoki , Umehara Takashi , Matsuo Jun‐ichi
Published: January 2021

Nucleophilic aromatic substitution of a dialkyl diselenide with 1‐bromo‐2,4‐dinitrobenzene and sodium borohydride in EtOH/THF proceeded chemoselectively in the presence of a thiol, an amine, and a carboxylic acid. ε‐N,N,N‐Trimethyllysine derivative was synthesized from selenohomocysteine dimer by the present arylation, oxidation, cross‐metathesis with 4‐iodobutene, reduction, and substitution with trimethylamine.
Three‐Component Synthesis of 2‐Substituted Thiobenzoazoles Using Tetramethyl Thiuram Monosulfide (TMTM) as Thiocarbonyl Surrogate
Authors: Wang Xi , Wu Chun‐Yan , Li Yue‐Sheng , Dong Zhi‐Bing
Published: January 2021

A metal‐free synthesis of 2‐benzyl/allyl‐substituted thiobenzoazoles was developed starting from tetramethyl thiuram monosulfide (TMTM) which served as thiocarbonyl surrogate. By using 2‐aminophenols (or 2‐aminothiophenols, or 1,2‐phenylenediamines) and TMTM as starting materials, 2‐mercaptobenzoazoles could be synthesized efficiently. The subsequent C–S bond formation with benzyl/allyl halides gave the final products (2‐benzyl/allyl‐substituted thiobenzoazoles) with good to excellent yields. The metal‐free conditions, inexpensive and easily available starting materials, and broad substrate scope are the advantageous features of this protocol.
Isobenzofurans as Synthetic Intermediates: Synthesis and Biological Activity of 8‐epi‐(–)‐Ajudazol B
Authors: Adair Liam , Egan Ben A. , Pearson Colin M. , Lopez‐Gonzalez Ricardo , Kuchar Michal , Mendoza‐Mendoza Artemio , Prunet Joëlle , Marquez Rodolfo
Published: January 2021

Ajudazol B is a polyketide secondary metabolite, isolated from the myxobacterium Chondromyces crocatus, that exhibits potent biological activity. Herein, we report a convergent total synthesis of 8‐epi‐(–)‐ajudazol B. The key step is a regio‐selective alkylation and oxidative rearrangement of a reactive isobenzofuran intermediate that generates the isochromanone core. This approach provides a fast and efficient method to synthesise analogues of ajudazol B from simple aldehydes, allowing assessment of structure‐activity relationships. The antifungal activity of 8‐epi‐(–)‐ajudazol B as well as that of related analogues has been assessed using Botrytis cinerea. The results indicate that the isochromanone unit is key for antifungal activity.