Catalyst-free synthesis of imidazo [1,2-a] pyridines via Groebke multicomponent reaction

Abstract

Deep eutectic solvents are becoming more popular nowadays since they are green, safe and often save raw materials and energy compared to organic solvent. Due to the importance of environmentally compatible solvent in multicomponent reactions, herein we report an efficient and sustainable catalyst-free synthesis of imidazo [1,2-a] pyridines via Groebke multicomponent reaction in choline chloride-based deep eutectic solvent. One-pot, three-component reaction of 2-amino pyridine, aromatic aldehydes and cyclohexyl isocyanide in six different choline chloride-based deep eutectic solvents in the absence of catalyst were examined. Urea–choline chloride was selected as an efficient solvent for this isocyanide-based multicomponent reaction and afforded the imidazo [1,2-a] pyridines in good yields of 57–87 % and reaction times of 2–6 h. The method has several advantages such as environmentally benign and biodegradable solvent, easy purification processes by a simple filtration and methodological simplicity.