# Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones

Karima Boussafi, Didier Villemin, Nathalie Bar

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Karima Boussafi, Didier Villemin, Nathalie Bar. Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones. 2023, 10.3390/ecsoc-27-16154. [hal-04416055](https://hal-04416055)

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# Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones

Karima Boussafi, Didier Villemin, Nathalie Bar

► To cite this version:

Karima Boussafi, Didier Villemin, Nathalie Bar. Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones. 2023, 10.3390/ecsoc-27-16154. [hal-04416055](https://hal-04416055)

HAL Id: hal-04416055

https://normandie-univ.hal.science/hal-04416055v1

Submitted on 25 Jan 2024

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
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publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
Proceeding Paper

# Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones †

Karima Boussafi 1,2, Didier Villemin 1,* and Nathalie Bar 1

**Abstract:** Aurones are natural bioactive dyes found in plants, and many of them are biologically active. We reported herein that α,β-dicarbonyl compounds condense with 3-coumarones without a solvent under microwave irradiation with clay as a catalyst. Novel acylaurones were obtained in good yields; the more stable *E*-isomer was formed stereoselectively.

**Keywords:** aurone; clay catalysis; coumaranone; microwave

## 1. Introduction

Aurones are natural products [1], and some aurone derivatives have been used recently in medicinal chemistry [2,3]. The aurones were generally synthesized by condensation of coumaran-3-ones with aldehydes under acido-basic conditions [4–6]. While ketones generally do not condense easily in these conditions with 3-coumaranones, we report herein that the more electrophilic α,β-dicarbonyl compounds [7] lead to these condensations providing new tetrasubstituted aurones. To our knowledge, the tetrasubstituted aurones already described in the literature were obtained only via ring formation [8].

In order to avoid the benzylic rearrangement [9] of the α,β-dicarbonyl compounds in a basic medium, we have preferred to use acidic catalysis rather than a basic one. Since 1989 [10], we have described the clays as good catalysts in a solvent-free Knoevenagel reaction under microwave irradiation (Scheme 1).

<figure><img src="image_2.png" /><figcaption>**Scheme 1.** Acidic catalyzed condensation of 3-coumaranone with α,β-dicarbonyl compounds.</figcaption></figure>

## 2. Results and Discussion

According to this methodology, an equimolar mixture of benzofuran-3(2H)-one and a dicarbonyl compound adsorbed on clay in a closed tube was irradiated using a microwave at 2450 MHz in a resonance cavity Anton Paar Monowave 300. The reactions of coumaranone 1a and benzil 2a are used as a model reaction to test the clays K10, KSF, or Algerian clay of Maghnia (Maghia) treated with sulphuric acid [11] as a catalyst. All these clays conduct similar yields (around 80%) after microwave irradiation.

<figure><img src="image_3.png" /></figure>

check for
updates

**Citation:** Boussafi, K.; Villemin, D.; Bar, N. Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones. *Chem. Proc.* **2023**, *14*, 32. https://doi.org/10.3390/ecsoc-27-16154

Academic Editor: Julio A. Seijas

Published: 15 November 2023

<figure><img src="image_4.png" /></figure>

**Copyright:** © 2023 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/).

<footnote n="1">1 Laboratoire de Chimie Moléculaire et Thioorganique, UMR CNRS 6507, INC3M, FR 3038, ENSICAEN et Université de Caen Normandie, 14050 Caen, France; boussafi.karima@yahoo.fr (K.B.); nathalie.bar@ensicaen.fr (N.B.)</footnote>

<footnote n="2">2 Algeria, Département de Chimie, Faculté des Sciences Exactes et Informatique, Université Mohamed Seddik Ben Yahia Jijel, Jijel 18000, Algeria</footnote>

<footnote>* Correspondence: didier.villemin@ensicaen.fr</footnote>

<footnote>† Presented at the 27th International Electronic Conference on Synthetic Organic Chemistry (ECSOC-27), 15–30 November 2023; Available online: https://ecsoc-27.sciforum.net/.</footnote>
Proceeding Paper

# Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones †

Karima Boussafi 1,2, Didier Villemin 1,* and Nathalie Bar 1

**Abstract:** Aurones are natural bioactive dyes found in plants, and many of them are biologically active. We reported herein that α,β-dicarbonyl compounds condense with 3-coumarones without a solvent under microwave irradiation with clay as a catalyst. Novel acylaurones were obtained in good yields; the more stable *E*-isomer was formed stereoselectively.

**Keywords:** aurone; clay catalysis; coumaranone; microwave

## 1. Introduction

Aurones are natural products [1], and some aurone derivatives have been used recently in medicinal chemistry [2,3]. The aurones were generally synthesized by condensation of coumaran-3-ones with aldehydes under acido-basic conditions [4–6]. While ketones generally do not condense easily in these conditions with 3-coumaranones, we report herein that the more electrophilic α,β-dicarbonyl compounds [7] lead to these condensations providing new tetrasubstituted aurones. To our knowledge, the tetrasubstituted aurones already described in the literature were obtained only via ring formation [8].

In order to avoid the benzylic rearrangement [9] of the α,β-dicarbonyl compounds in a basic medium, we have preferred to use acidic catalysis rather than a basic one. Since 1989 [10], we have described the clays as good catalysts in a solvent-free Knoevenagel reaction under microwave irradiation (Scheme 1).

<figure><img src="image_2.png" /><figcaption>**Scheme 1.** Acidic catalyzed condensation of 3-coumaranone with α,β-dicarbonyl compounds.</figcaption></figure>

## 2. Results and Discussion

According to this methodology, an equimolar mixture of benzofuran-3(2H)-one and a dicarbonyl compound adsorbed on clay in a closed tube was irradiated using a microwave at 2450 MHz in a resonance cavity Anton Paar Monowave 300. The reactions of coumaranone **1a** and benzil **2a** are used as a model reaction to test the clays K10, KSF, or Algerian clay of Maghnia (Maghia) treated with sulphuric acid [11] as a catalyst. All these clays conduct similar yields (around 80%) after microwave irradiation.

<figure><img src="image_3.png" /></figure>

check for
updates

**Citation:** Boussafi, K.; Villemin, D.; Bar, N. Clay Catalysis: Solventless Condensation of Benzofuran-3(2H)-One with α,β-Dicarbonyl Compounds under Microwave Irradiation: Synthesis of New Acyl-Aurones. *Chem. Proc.* **2023**, *14*, 32. https://doi.org/10.3390/ecsoc-27-16154

Academic Editor: Julio A. Seijas

Published: 15 November 2023

<figure><img src="image_4.png" /></figure>

**Copyright:** © 2023 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/).

<footnote n="1">1 Laboratoire de Chimie Moléculaire et Thioorganique, UMR CNRS 6507, INC3M, FR 3038, ENSICAEN et Université de Caen Normandie, 14050 Caen, France; boussafi.karima@yahoo.fr (K.B.); nathalie.bar@ensicaen.fr (N.B.)</footnote>

<footnote n="2">2 Algeria, Département de Chimie, Faculté des Sciences Exactes et Informatique, Université Mohamed Seddik Ben Yahia Jijel, Jijel 18000, Algeria</footnote>

<footnote>* Correspondence: didier.villemin@ensicaen.fr</footnote>

<footnote>† Presented at the 27th International Electronic Conference on Synthetic Organic Chemistry (ECSOC-27), 15–30 November 2023; Available online: https://ecsoc-27.sciforum.net/.</footnote>
Under these conditions, novel acylaurones not previously described were prepared according to Scheme 1. The irradiation conditions and the yields are reported in Table 1. The new products were characterized using mass spectroscopy, ¹H, and ¹³C NMR spectroscopy.

<table><caption>**Table 1.** Synthesis of new acylaurones under microwave activation.</caption><thead><tr><th>Coumaranone 1a–b</th><th>α,β-dicarbonyl 2</th><th>Conditions</th><th>Product, Yield %</th></tr></thead><tbody><tr><td>1a</td><td>2a</td><td>200 °C, 15 min</td><td>3a, 80</td></tr><tr><td>1a</td><td>2b</td><td>200 °C, 10 min</td><td>3a, 75</td></tr><tr><td>1a</td><td>2c</td><td>200 °C, 10 min</td><td>3a, 72</td></tr><tr><td>1a</td><td>2d</td><td>200 °C, 10 min</td><td>3d, 70</td></tr><tr><td>1a</td><td>2e</td><td>200 °C, 15 min</td><td>3e, 70</td></tr><tr><td>1b</td><td>2a</td><td>180 °C, 10 min</td><td>3f, 67</td></tr><tr><td>1b</td><td>2b</td><td>180 °C, 10 min</td><td>3g, 65</td></tr><tr><td>1b</td><td>2c</td><td>180 °C, 10 min</td><td>3h, 63</td></tr><tr><td>1b</td><td>2d</td><td>180 °C, 10 min</td><td>3i, 60</td></tr><tr><td>1b</td><td>2f</td><td>180 °C, 10 min</td><td>3j, 70</td></tr><tr><td>1c</td><td>2a</td><td>180 °C, 10 min</td><td>3k, 65</td></tr><tr><td>1c</td><td>2b</td><td>180 °C, 10 min</td><td>3l, 80</td></tr></tbody></table>

### 3. Mechanisms

A probable mechanism for this acidic condensation involves the addition of an α-hydroxy-acylium cation on the enol form of the 3-coumaranone according to Scheme 2:

<figure><img src="image_5.png" /><figcaption>**Scheme 2.** Probable mechanism of acidic catalyzed condensation of 3-coumaranone with α,β-dicarbonyl compounds.</figcaption></figure>
Under these conditions, novel acylaurones not previously described were prepared according to Scheme 1. The irradiation conditions and the yields are reported in Table 1. The new products were characterized using mass spectroscopy, ¹H, and ¹³C NMR spectroscopy.

<table><caption>**Table 1.** Synthesis of new acylaurones under microwave activation.</caption><thead><tr><th>Coumaranone 1a–b</th><th>α,β-dicarbonyl 2</th><th>Conditions</th><th>Product, Yield %</th></tr></thead><tbody><tr><td>1a</td><td>2a</td><td>200 °C, 15 min</td><td>3a, 80</td></tr><tr><td>1a</td><td>2b</td><td>200 °C, 10 min</td><td>3a, 75</td></tr><tr><td>1a</td><td>2c</td><td>200 °C, 10 min</td><td>3a, 72</td></tr><tr><td>1a</td><td>2d</td><td>200 °C, 10 min</td><td>3d, 70</td></tr><tr><td>1a</td><td>2e</td><td>200 °C, 15 min</td><td>3e, 70</td></tr><tr><td>1b</td><td>2a</td><td>180 °C, 10 min</td><td>3f, 67</td></tr><tr><td>1b</td><td>2b</td><td>180 °C, 10 min</td><td>3g, 65</td></tr><tr><td>1b</td><td>2c</td><td>180 °C, 10 min</td><td>3h, 63</td></tr><tr><td>1b</td><td>2d</td><td>180 °C, 10 min</td><td>3i, 60</td></tr><tr><td>1b</td><td>2f</td><td>180 °C, 10 min</td><td>3j, 70</td></tr><tr><td>1c</td><td>2a</td><td>180 °C, 10 min</td><td>3k, 65</td></tr><tr><td>1c</td><td>2b</td><td>180 °C, 10 min</td><td>3l, 80</td></tr></tbody></table>

### 3. Mechanisms

A probable mechanism for this acidic condensation involves the addition of an α-hydroxy-acylium cation on the enol form of the 3-coumaranone according to Scheme 2:

<figure><img src="image_5.png" /><figcaption>**Scheme 2.** Probable mechanism of acidic catalyzed condensation of 3-coumaranone with α,β-dicarbonyl compounds.</figcaption></figure>
## 4. Stereochemistry

Two stereoisomers can be formed in the acidic catalyzed condensation of 3-coumaranone with carbonyl compounds. In the case of aldehydes, only the more stable Z-isomer was produced. In the case of α,β-dicarbonyl compounds, only one stereoisomer was formed (TLC, NMR). We focused on the case of the two stereoisomers of **3a**, and we have predicted the ¹³C NMR spectra of Z and E **3a** with Spartan software [12]: the more stable E-isomer displays a ¹³C NMR spectrum corresponding to the compound found.

## 5. Experimental

### 5.1. General Information

The ¹H NMR and ¹³C NMR spectra were recorded on a Brüker AC 400 spectrometer at 400 MHz. Samples were recorded in CDCl₃ solutions using TMS as an internal standard. The chemical shifts are expressed in δ units (ppm) and quoted downfield from TMS. The multiplicities are reported as s, singlet; d, doublet; t, triplet; q, quartet; and m, multiplet.

Mass spectra were recorded on Xevo G2-XS QToF Waters.

Microwave irradiations were performed at 2450 MHz with an Anton-Paar Monowave 300.

Computation was performed with Spartan 14 software (DFT, with B3LYP 3-21G basis) on a Dell workstation.

### 5.2. Starting Reactants

The 6-hydroxybenzofuran-3(2H)-one (1b) and 6-methoxybenzofuran-3(2H)-one (1c) were prepared according to the literature. Benzofuran-3(2H)-one (1a), isatin (2d), bromo-5-isatin (2f), benzil (2a), phenanthraquinone (2b), acenaphthoquinone (2c), and ninhydrine (2e) are commercial (Alfa).

Clays used: the Algerian clay of Maghnia was treated with sulfuric acid according to the conditions described by us in the literature [11]. K10 and KSF clays (Süd Chemie) are commercially available from Aldrich.

### 5.3. Typical Experiment

The mixture of dicarbonyl compound **2** (1 mmol) and 3-coumaranone **1a** (1 mmol) was dissolved in methanol (10 mL), the clay K10 (2 g) was added, and the solvent was evaporated under vacuum with a rotary evaporator. The powder placed in a G10 tube was irradiated using a microwave (see conditions Table 1) with a Monowave 300 of Anton Paar. The powder was extracted with methanol (3 × 20 mL), and the solvent was evaporated. The resulting solid was chromatographed using preparative TLC (AcOEt/cyclohexane = 1/3). The colored acylaurones (orange to red) were characterized by ¹H, ¹³C NMR, and mass spectroscopy.

For example:

(E)-2-(2-oxo-1,2-diphenylethylidene)benzofuran-3(2H)-one (3a)

Obtained from benzil **2a** and 3-coumaranone **1a** as an orange solid, C₂₂H₁₄O₃, Mp = 175 °C; Rf = 0.64 (AcOEt).

¹H NMR: (400 MHz, CD₃Cl) δ 8.07 (m, 1Har); 7.88 (m, 1Har); 7.72 (m, 1Har); 7.63 (m, 1Har); 7.55 (m, 1Har); 7.54 (m, 1Har); and 7.46 (m, 1Har).

¹³C NMR: (400 MHz, CD₃Cl) δ 197.5 (CO); 182.6 (CO), 163.4, 156.2, 137.9, 135.2; 134.5; 132.6; 129.2; 128.9; 128.6; 128.5; 123.4; and 119.1

HRMS (M+1): 327.1021 calculated for C₂₂H₁₄O₃; found: 327.1020.

IR (cm⁻¹): 1681 (νCO); 1668 (νCO; 1600-1450(νC=C)); and 1220 (-O-C).

**Author Contributions:** Conceptualization, D.V.; investigation, K.B.; writing—review and editing, D.V. and N.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.
## 4. Stereochemistry

Two stereoisomers can be formed in the acidic catalyzed condensation of 3-coumaranone with carbonyl compounds. In the case of aldehydes, only the more stable Z-isomer was produced. In the case of α,β-dicarbonyl compounds, only one stereoisomer was formed (TLC, NMR). We focused on the case of the two stereoisomers of **3a**, and we have predicted the ¹³C NMR spectra of Z and E **3a** with Spartan software [12]: the more stable E-isomer displays a ¹³C NMR spectrum corresponding to the compound found.

## 5. Experimental

### 5.1. General Information

The ¹H NMR and ¹³C NMR spectra were recorded on a Brüker AC 400 spectrometer at 400 MHz. Samples were recorded in CDCl₃ solutions using TMS as an internal standard. The chemical shifts are expressed in δ units (ppm) and quoted downfield from TMS. The multiplicities are reported as s, singlet; d, doublet; t, triplet; q, quartet; and m, multiplet.

Mass spectra were recorded on Xevo G2-XS QToF Waters.

Microwave irradiations were performed at 2450 MHz with an Anton-Paar Monowave 300.

Computation was performed with Spartan 14 software (DFT, with B3LYP 3-21G basis) on a Dell workstation.

### 5.2. Starting Reactants

The 6-hydroxybenzofuran-3(2H)-one (**1b**) and 6-methoxybenzofuran-3(2H)-one (**1c**) were prepared according to the literature. Benzofuran-3(2H)-one (**1a**), isatin (**2d**), bromo-5-isatin (**2f**), benzil (**2a**), phenanthraquinone (**2b**), acenaphthoquinone (**2c**), and ninhydrine (**2e**) are commercial (Alfa).

Clays used: the Algerian clay of Maghnia was treated with sulfuric acid according to the conditions described by us in the literature [11]. K10 and KSF clays (Süd Chemie) are commercially available from Aldrich.

### 5.3. Typical Experiment

The mixture of dicarbonyl compound **2** (1 mmol) and 3-coumaranone **1a** (1 mmol) was dissolved in methanol (10 mL), the clay K10 (2 g) was added, and the solvent was evaporated under vacuum with a rotary evaporator. The powder placed in a G10 tube was irradiated using a microwave (see conditions Table 1) with a Monowave 300 of Anton Paar. The powder was extracted with methanol (3 × 20 mL), and the solvent was evaporated. The resulting solid was chromatographed using preparative TLC (AcOEt/cyclohexane = 1/3). The colored acylaurones (orange to red) were characterized by ¹H, ¹³C NMR, and mass spectroscopy.

For example:

(E)-2-(2-oxo-1,2-diphenylethylidene)benzofuran-3(2H)-one (**3a**)

Obtained from benzil **2a** and 3-coumaranone **1a** as an orange solid, C₂₂H₁₄O₃, Mp = 175 °C; Rf = 0.64 (AcOEt).

¹H NMR: (400 MHz, CD₃Cl) δ 8.07 (m, 1Har); 7.88 (m, 1Har); 7.72 (m, 1Har); 7.63 (m, 1Har); 7.55 (m, 1Har); 7.54 (m, 1Har); and 7.46 (m, 1Har).

¹³C NMR: (400 MHz, CD₃Cl) δ 197.5 (CO); 182.6 (CO), 163.4, 156.2, 137.9, 135.2; 134.5; 132.6; 129.2; 128.9; 128.6; 128.5; 123.4; and 119.1

HRMS (M+1): 327.1021 calculated for C₂₂H₁₄O₃; found: 327.1020.

IR (cm⁻¹): 1681 (νCO); 1668 (νCO; 1600-1450(νC=C)); and 1220 (-O-C).

**Author Contributions:** Conceptualization, D.V.; investigation, K.B.; writing—review and editing, D.V. and N.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.
**Data Availability Statement:** Data sharing is not applicable to this article.

**Acknowledgments:** The authors thank Karine Jarsalé for mass spectrometry spectra.

**Conflicts of Interest:** The authors declare no conflict of interest.

## References

1. Ikans, R. *Natural Compounds: An Laboratory Guide*; Academic Press: San Diego, CA, USA, 1991.

2. Mazziotti, I.; Petrarolo, G.; La Motta, C. Aurones: A Golden Resource for Active Compounds. *Molecules* **2022**, *27*, 2. [CrossRef] [PubMed]

3. Sui, G.; Li, T.; Zhang, B.; Wang, R.; Hao, H.; Zhou, W. Recent advances on synthesis and biological activities of aurones. *Bioorg. Med. Chem.* **2021**, *29*, 115895. [CrossRef] [PubMed]

4. Varma, R.S.; Varma, M. Alumina-mediated condensation. A simple synthesis of aurones. *Tetrahedron Lett.* **1992**, *33*, 5937–5940. [CrossRef]

5. Villemin, D.; Martin, B.; Bar, N. Application of microwave in organic synthesis: Dry synthesis of 2-arylmethylene-3(2)-naphthofuranones. *Molecules* **1998**, *3*, 88–93. [CrossRef]

6. Boussafi, K.; Villemin, D.; Bar, N.; Belghobsi, M. Green Synthesis of Aurones and Related Compounds under Solvent-free Conditions. *J. Chem. Res.* **2016**, *40*, 557–569. [CrossRef]

7. Junek, H.; Hamböck, H.; Hornischer, B. Synthesen mit Nitrilen, 12. Mitt.: Die Malonitrilylidenverbindungen des Phenanthren-und Acenaphthenchinons. *Monatshefte Chem.* **1967**, *98*, 315–323. [CrossRef]

8. Lin, C.F.; Lu, W.D.; Wang, I.W.; Wu, M.J. Synthesis of 2-(Diarylmethylene)-3-benzofuranones Promoted via Palladium-Catalyzed Reactions of Aryl iodides with 3-Aryl-1-(2-tert-butyldimethyl-silyloxy) phenyl-2-propyn-1-ones. *Synlett* **2003**, *13*, 2057–2061. [CrossRef]

9. Selman, S.; Eastham, J.F. Benzilic acid and related rearrangements. *Q. Rev. Chem. Soc.* **1960**, *14*, 221–235. [CrossRef]

10. Ben Alloum, A.; Labiad, B.; Villemin, D. Application of microwave heating techniques for dry organic reactions. *J. Chem. Soc. Chem. Commun.* **1989**, *7*, 386–387. [CrossRef]

11. Didi, M.A.; Makhoukhi, B.; Azzouz, A.; Villemin, D. Colza oil bleaching through optimized acid activation of bentonite. A comparative study. *Appl. Clay Sci.* **2009**, *42*, 336–344. [CrossRef]

12. Spartan Wavefunction. Available online: https://www.wavefun.com/ (accessed on 12 July 2023).

**Disclaimer/Publisher's Note:** The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.
**Data Availability Statement:** Data sharing is not applicable to this article.

**Acknowledgments:** The authors thank Karine Jarsalé for mass spectrometry spectra.

**Conflicts of Interest:** The authors declare no conflict of interest.

## References

1. Ikans, R. *Natural Compounds: An Laboratory Guide*; Academic Press: San Diego, CA, USA, 1991.

2. Mazziotti, I.; Petrarolo, G.; La Motta, C. Aurones: A Golden Resource for Active Compounds. *Molecules* **2022**, *27*, 2. [CrossRef] [PubMed]

3. Sui, G.; Li, T.; Zhang, B.; Wang, R.; Hao, H.; Zhou, W. Recent advances on synthesis and biological activities of aurones. *Bioorg. Med. Chem.* **2021**, *29*, 115895. [CrossRef] [PubMed]

4. Varma, R.S.; Varma, M. Alumina-mediated condensation. A simple synthesis of aurones. *Tetrahedron Lett.* **1992**, *33*, 5937–5940. [CrossRef]

5. Villemin, D.; Martin, B.; Bar, N. Application of microwave in organic synthesis: Dry synthesis of 2-arylmethylene-3(2)-naphthofuranones. *Molecules* **1998**, *3*, 88–93. [CrossRef]

6. Boussafi, K.; Villemin, D.; Bar, N.; Belghobsi, M. Green Synthesis of Aurones and Related Compounds under Solvent-free Conditions. *J. Chem. Res.* **2016**, *40*, 557–569. [CrossRef]

7. Junek, H.; Hamböck, H.; Hornischer, B. Synthesen mit Nitrilen, 12. Mitt.: Die Malonitrilylidenverbindungen des Phenanthren-und Acenaphthenchinons. *Monatshefte Chem.* **1967**, *98*, 315–323. [CrossRef]

8. Lin, C.F.; Lu, W.D.; Wang, I.W.; Wu, M.J. Synthesis of 2-(Diarylmethylene)-3-benzofuranones Promoted via Palladium-Catalyzed Reactions of Aryl iodides with 3-Aryl-1-(2-tert-butyldimethyl-silyloxy) phenyl-2-propyn-1-ones. *Synlett* **2003**, *13*, 2057–2061. [CrossRef]

9. Selman, S.; Eastham, J.F. Benzilic acid and related rearrangements. *Q. Rev. Chem. Soc.* **1960**, *14*, 221–235. [CrossRef]

10. Ben Alloum, A.; Labiad, B.; Villemin, D. Application of microwave heating techniques for dry organic reactions. *J. Chem. Soc. Chem. Commun.* **1989**, *7*, 386–387. [CrossRef]

11. Didi, M.A.; Makhoukhi, B.; Azzouz, A.; Villemin, D. Colza oil bleaching through optimized acid activation of bentonite. A comparative study. *Appl. Clay Sci.* **2009**, *42*, 336–344. [CrossRef]

12. Spartan Wavefunction. Available online: https://www.wavefun.com/ (accessed on 12 July 2023).

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