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 arylidenepyrazolones 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.