Ultrasound-assisted synthesis of imidazo[1,2-a]pyridines and sequential one-pot preparation of 3-selanyl-imidazo[1,2-a]pyridine derivatives

Abstract

A simple and rapid method to synthesize imidazo[1,2-a]pyridines starting from 2-aminopyridine and 2bromoacetophenone derivatives under ultrasonic irradiation was developed. This protocol tolerates a wide range of 2-bromoacetophenone derivatives to produce a variety of imidazo[1,2-a]pyridines in good to excellent yields. Additionally, the one-pot preparation of 3-(organylselanyl)imidazo[1,2-a]pyridines via a sequential method is presented. In this case, different diorganyl diselenides were used as starting material s to afford the corresponding coupling products in excellent yields and short reaction times under sonication. The reactions were conducted in PEG-400, a cheap and nontoxic solvent, compatible with the ultrasound conditions in an environmentally benign process.

Transition-Metal-Catalyzed C–S, C–Se, and C–Te Bond Formations via Cross-Coupling and Atom-Economic Addition Reactions. Achievements and Challenges

“…The output is lower with S, and with Te, the reaction does not proceed at all (Scheme 168, A). 637 A multicomponent reaction catalyzed by CuI in the presence of BF 3 •OEt 2 yielded sulfenylimidazo[1,2-a]pyridines in moderate to high yields (38−91%) (Scheme 168, B). 638 On the other hand, heteroarenes with a sufficiently acidic CH bond for which organocopper compounds are formed as a result of deprotonation under the action of a base undergo direct thiolation.…”

“…A one-pot process for producing substituted imidazo­[1,2- a ]­pyridines and their selenylation at position 3 (17 compounds) was described by Schumacher, Lenardão, and co-workers. The output is lower with S, and with Te, the reaction does not proceed at all (Scheme , A) …”

Recent Advances in the Synthesis of Imidazo[1,2‐a]pyridines: A Brief Review

“…[231] Recently, sonochemistry has proven itself as an essential tool in drug discovery and green organic synthesis as reactions promoted by ultrasound are faster. [232] To develop a green procedure for the synthesis of organo-chalcogen containing N-heterocycles, [233] Vieira et al [234] in 2019 reported a one-pot ultrasound-mediated synthesis of imidazo[1,2a]pyridines 308 from 2-aminopyridine 12 and 2-bromoacetophenone derivatives 307 in air atmosphere using PEG-400 as a non-toxic solvent in good to excellent yields. The author has also reported the synthesis of 3-selanyl imidazo To develop a simple and green synthetic protocol, Bhutia et al in 2020 reported a novel environmentally sustainable I 2promoted efficient synthesis of 2-arylimidazo[1,2-a]-pyridine derivatives 314 by condensation of various aryl methyl ketones 312/312' with 2-aminopyridine derivatives 313 at room temperature in aqueous media and by mild heating in SDS-derived micellar media in good to excellent yields.…”

Microwave‐assisted synthesis and luminescent activity of imidazo[1,2‐a]pyridine derivatives

“…The chemistry of imidazopyridines has been studied since the beginning of this century. Accordingly, the most widely used and practical synthesis routes are the condensation between α‐halocarbonyls and 2‐aminopyridine where Vieira et al employed ultrasound as an alternative energy in a basic medium (Scheme A). On the other hand, Jadhav et al used water and polyethylene glycol as solvent in a one‐pot reaction avoiding the synthesis of the α‐halocarbonyl (Scheme B).…”