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An efficient one-pot synthesis of spiro[indoline-3,4'-pyrano[2,3-c]pyrazole] derivatives by four-component reaction of hydrazine, β-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.
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Zou et al. (2011) studied this question.
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