Bronsted acidic ionic liquid catalyzed tandem reaction of 4-hydroxy-1-methyl-2-quinolone with chalcone: regioselective synthesis of pyrano[3,2-c] quinolin-2-ones

A new methodology has been developed for the synthesis of pyrano [3,2-c]quinolin-2-one derivatives by the tandem cyclization of 4-hydroxy-1-methyl-2-quinolone with chalcones using a catalytic amount of task specific ionic liquid [1-methyl-3-(4-sulfobutyl)imidazolium-4-methylbenzenesulfonate] under solvent-free conditions. The developed protocol is applicable for the construction of pyrano [3,2-c]quinolin-2-ones from easily accessible chalcones having aryl and hetero aryl substituents. This reaction possibly proceeds through Michael addition followed by cyclization. The feasibility of the catalyst recycling is also demonstrated. This method produced only water as the byproduct and represents a green synthetic protocol.