Bronsted Acid-Catalyzed Four-Component Cascade Reaction: Facile Synthesis of Hexahydroimidazo[1,2-a]pyridines

An efficient four-component cascade reaction for the synthesis of trisubstituted hexahydroimidazo[1,2-a]pyridines starting from readily available aldehydes, ketones and ethane-1,2-diamine catalyzed by p-toluenesulfonic acid is described. Two new cycles and five new bonds are constructed with all reactants being efficiently utilized in this transformation. The mechanism of the reaction was investigated and some crucial reaction intermediates were observed.