Step-economical and Metal-free One-pot Access to 2-Aryl-3-(arylthio)imidazo[1,2-a]pyridines via Neutral Ionic Liquid-mediated Cyclocondensation–Sulfenylation

Abstract A practical and straightforward metal-free, one-pot protocol has been developed for the synthesis of 3-sulfenylimidazo[1,2-a]pyridines using the neutral ionic liquid [hmim]Br as both solvent and dual-function promoter. This efficient method integrates cyclocondensation and sulfenylation into a single operation, enabling simultaneous C–N and C–S bond formation without the need for transition-metal catalysts or external oxidants. The reaction proceeds smoothly with readily accessible 2-aminopyridine, phenacyl bromide, and arylsulfonyl chloride, the latter being transformed in situ into a thiol equivalent under the same mild and neutral reaction conditions. The protocol also accommodates arylsulfonyl hydrazide and sodium aryl sulfinate as alternative sulfenylating agents. Overall, this one-pot sequential approach offers good functional-group tolerance and a broad substrate scope, avoids hazardous reagents, and aligns well with green chemistry principles through step economy and operational simplicity.