Organocatalyzed enantioselective synthesis of 6-amino-5-cyanodihydropyrano[2,3-c]pyrazoles

The first enantioselective synthesis of biologically active 6-amino-5-cyanodihydropyrano[2,3-c]pyrazoles has been achieved through a cinchona alkaloid-catalyzed tandem Michael addition and Thorpe-Ziegler type reaction between 2-pyrazolin-5-ones and benzylidenemalononitriles. The reaction may also be carried out in a three-component or a four-component fashion via the in situ formation of these two components from simple and readily available starting materials. The desired products were obtained in excellent yields with mediocre to excellent enantioselectivities (up to >99% ee). (C) 2009 Elsevier Ltd. All rights reserved.