Enantioselective Synthesis of N-Phenyl-dihydropyrano[2,3-c]-pyrazoles via Cascade Michael Addition/Thorpe-Ziegler Type Cyclization Catalyzed by a Chiral Squaramide

Enantioselective synthesis of biologically active dihydropyrano[2,3-c]pyrazoles has been achieved through a squaramide-catalysed Michael addition/Thorpe-Ziegler type cyclization cascade reaction between arylidenepyra-zolones and malononitrile.A series of optically active dihydropyano[2,3-c]pyrazoles were obtained in excellent yields(up to 99%)and moderate to good enantioselectivities(up to 79%ee)under mild reaction conditions.