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

Abstract

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.

Multicomponent Strategy to Pyrazolo[3,4-b]pyrrolo[3,4-d]pyridine Derivatives under Microwave Irradiation

“…Next, this reaction was carried out in EtOH with HCOOH, C 6 H 5 COOH, fumaric acid, and l -proline as catalysts, and these cases scarcely proceeded (Table , entries 5–8). Through previous literature review, it was found that HOAc can be used as a solvent, as well as a catalyst. − Next, this chemistry was carried out in HOAc, it gave the 55% yield of 4a (Table , entry 9). Subsequently, the influence of reaction temperature was also optimized.…”

p‐Toluenesulfonic acid catalyzed, isocyanide‐free, Groebke–Blackburn–Bienayme (GBB) type multicomponent synthesis of 3‐anilino‐imdazo[1,2‐a]pyridines

“…This could be due to the reaction of p ‐carbon of N‐methyl aniline with glyoxal instead of aniline nitrogen followed by air oxidation to form alcohol to ketone. 1,2‐Diketone types of product synthesis using glyoxals are reported by Kumar and coworkers [17]. Later to prove the application of the reaction, a gram‐scale synthesis of product 4a was carried out under the optimized reaction conditions, which provided 77% yield as mentioned in Scheme 4.…”