Gold-catalyzed oxidation of terminal alkynes to glyoxals and their reactions with 2-phenylimidazo[1,2-a]pyridines: one-pot synthesis of 1,2-diones

A novel one-pot protocol for the convenient and efficient synthesis of (2-phenylimidazo[1,2-a]pyridin-3-yl)alkane-1,2-diones (3) in good yields (32-88%) from 2-phenylimidazo[1,2-a]pyridines (1) and terminal alkynes (2) has been established with a wide range of substrate scope. A tandem reaction sequence containing gold-catalyzed double oxidations of terminal alkynes to generate glyoxals, nucleophilic addition of 2-phenylimidazo[1,2-a]pyridines to glyoxals to yield α-hydroxyl ketones, and oxygenation of the α-hydroxyl ketones to afford the final products 3 under air atmosphere is involved in this method. Simple operation, mild reaction conditions, and widely available substrates make this strategy more affordable.

Iodine-catalyzed α,β-dehydrogenation of ketones and aldehydes generating conjugated enones and enals

A transition metal-free α,β-dehydrogenation of ketones and aldehydes was developed.

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 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 chalcogenation of imidazoheterocycles with sulfur/selenium powder and coumarinyl triflates

An efficient and convenient copper-catalyzed chalcogenation of imidazoheterocycles with sulfur/selenium powder and coumarinyl triflates has been described.

FeCl3-Catalyzed Cross-Dehydrogenative Coupling between Imidazoheterocycles and Oxoaldehydes

An Fe(III)-catalyzed efficient dicarbonylation of imidazoheterocycles has been developed through cross-dehydrogenative coupling between imidazoheterocycles and oxoaldehydes under ambient air in high yields. The present protocol is also applicable to indolizines. Imidazopyridine produced bisimidazopyridine with arylaldehyde. Experimental results suggest that the reactions proceed through the nonradical pathway.

Intramolecular oxidative coupling: I2/TBHP/NaN3-mediated synthesis of benzofuran derivatives

A novel intramolecular oxidative coupling reaction has been established to prepare benzofuran derivatives via direct C(sp²)–H functionalization for the formation of C–O bonds. This transformation is mediated by I₂/TBHP/NaN₃ under metal-free conditions and a catalytic amount of NaN₃ plays a crucial role in the reaction.