Copper-catalyzed aerobic oxidative dicarbonylation of indoles utilizing α-carbonyl aldehydes

Synthetic routes to access dicarbonylated aryls and heteroaryls

1,2-Dicarbonyl compounds are privileged functionalities found in natural products, pharmaceuticals, bioactive molecules, and food items, and are important precursors in catalysis, asymmetric synthesis, polymer chemistry and synthesizing functionalized heterocycles. Herein, this comprehensive review focuses on various approaches for synthesizing 1,2-dicarbonylated aryls and heteroaryls in both intermolecular and intramolecular fashion, covering the dicarbonylation of indoles, imidazoheterocycles, indolizines, aminopyrazoles, pyrroloisoquinolines, coumarins, furan, anilines, phenols, anthranils, and benzil synthesis over the last decade (since 2015). Also, the present review highlights the scope and future perspectives of the approach.

Dual Role of Oxoaldehydes: Divergent Synthesis of 3-Aryl- and 3-Aroylcoumarins

A facile and efficient synthetic approach to various valuable 3-aryl- and 3-aroylcoumarins by the direct arylation and aroylation of coumarins with glyoxals in a metal-free manner is presented. The aryl glyoxal is for the first time recognized to serve as an aryl surrogate in addition to its role as an aroyl transfer reagent via a simple switch in reaction conditions. The approach accommodates a broad substrate scope and high yields of the two types of cross-coupling reactions starting from identical starting materials.

Catalyst-free direct cross-dehydrogenative coupling of imidazoheterocycles with glyoxal hydrates: an efficient approach to 1,2-diketones

An efficient and convenient methodology for catalyst-free cross-dehydrogenative coupling of imidazoheterocycles with glyoxal hydrates in good yields was developed. This methodology exhibits a broad substrate scope and excellent functional group tolerance and offers a straightforward means to produce different heterocycles such as imidazoheterocyclic quinoxaline, imidazoheterocyclic hydantoin and imidazoheterocyclic α-keto ketamine under relatively mild conditions. Biological evaluation showed that the most potent compound 3m possesses significant in vitro antiproliferative activities against human-derived lung cancer cell lines with an IC50 value of 14.8 μM.

Dual Role of Glyoxal in Metal-Free Dicarbonylation Reaction: Synthesis of Symmetrical and Unsymmetrical Dicarbonyl Imidazoheterocycles

A practical and efficient method has been developed for the dicarbonylation of imidazoheterocycles using glyoxals as dicarbonyl precursors under metal-free conditions in acetic acid. A series of symmetrical and unsymmetrical dicarbonyl imidazoheterocycles was synthesized in good yields. Aryl and alkyl glyoxals also demonstrated excellent reactivity under similar reaction conditions and delivered corresponding dicarbonyl imidazoheterocycles in high yields. It is believed that the glyoxal plays a dual role both as a dicarbonyl source and as an oxidant in this transformation. A probable mechanistic pathway has been proposed based on control experiments and electrospray ionization high-resolution mass spectrometry analysis.

Regioselective N-1 and C-2 diacylation of 3-substituted indoles with arylglyoxal hydrates for the synthesis of indolyl diketones

A highly regioselective N-1 and C-2 diacylation of 3-substituted indoles with arylglyoxal hydrates to afford N-1 and C-2 indolyl diketones in moderate to good yields is described. Notably, the control of regioselectivity is achieved by small changes in the Cu catalyst, additive and solvent. Importantly, the intermediates for N-1 and C-2 diacylation were detected and two plausible pathways were also proposed.

Regioselective oxidative cross-coupling of benzo[d]imidazo[2,1-b]thiazoles with styrenes: a novel route to C3-dicarbonylation

A novel I₂ promoted, highly efficient metal-free and peroxide-free greener domino protocol for the C3-dicarbonylation of benzo[d]imidazo[2,1-b]thiazoles (IBTs) with styrenes has been developed via oxidative cleavage of the C(sp²)-H bond, followed by C3-nucleophilic attack of IBT and oxidation. Interestingly, under these conditions 2-(benzo[d]imidazo[2,1-b]thiazol-2-yl)aniline gave the benzo[4',5']thiazolo[2',3':2,3]imidazo[4,5-c]quinoline derivative via oxidative cleavage of the C(sp²)-H bond, followed by Pictet-Spengler cyclization and aromatization. This method offers the advantages of broad substrate scope, ecofriendly feature and high atom economy apart from higher yields.

Copper-catalyzed synthesis of indolyl diketones via C–H oxidation/diacylation of indoles with arylglyoxal hydrates

Copper-catalyzed synthesis of indolyl diketonesviaC–H oxidation/diacylation of indoles with arylglyoxal hydrates is described.

The dicarbonylation of indoles via Friedel–Crafts reaction with dicarbonyl nitrile generated in situ and retro-cyanohydrination

The reaction of indole and β-carbonyl nitrile to generate dicarbonyl indoles has been developed. This process involves α-oxonation of the β-carbonyl nitrile, Friedel–Crafts reaction with indoles and retro-cyanohydrination form dicarbonyl indoles.