Rapid and Efficient Ultrasound-Assisted Method for the Combinatorial Synthesis of Spiro[indoline-3,4 '-pyrano[2,3-c]pyrazole] Derivatives

An efficient one-pot synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives by four-component reaction of hydrazine, beta-keto ester, isatin, and malononitrile or ethyl cyanoacetate catalyzed by piperidine under ultrasound irradiation is described. This synthesis was confirmed to follow the group-assistant-purification chemistry (GAP) chemistry process, which can avoid traditional chromatography and recrystallization purifications.