A facile and efficient procedure for one-pot four-component synthesis of polysubstituted spiro pyrano[2,3-c]pyrazole and spiro 1,4-dihydropyridine catalyzed by a Dabco-based ionic liquid under mild conditions

Abstract

A simple and efficient synthetic protocol for the syntheses of spiro pyrano[2,3-c]pyrazole and spiro 1,4-dihydropyridine derivatives via a one pot four-component reaction catalyzed by Dabco-based ionic liquids has been successfully developed. Under the same reaction conditions, when hydrazines were used as amine components to react with isatins, active methylenes and dialkyl acetylenedicarboxylates, the reactions afforded spiro pyrano[2,3-c]pyrazoles in good to excellent yields (78–96%). While aromatic amines were used as amine components in the same reaction, a completely different product scaffold of spiro 1,4-dihydropyridines was obtained in moderate to good yields (52–93%). This synthetic protocol could be applicable to a wide range of substrates. The desired products are easily separated and purified by simple crystallization. The catalyst could be recycled five times. Plausible reaction mechanisms were proposed according to the experimental results.