Acid-Catalyzed [3+2] Cycloaddition of Enones with Azomethine Imines for Easy Access to Tetrahydropyrazolopyrazolones

Abstract

Aluminum chloride (AlCl3) or zirconium chloride (ZrCl4) catalyzes efficiently the [3+2] cycloaddition of N,N′-cyclic azomethine imines with enones which contain the vinyl group. The scope of the reaction towards various azomethine imines and enones has been explored. Access to diastereomerically pure 6-acyl-5-aryltetrahydropyrazolo[1,2-a]pyrazol-1(5H)-ones is provided by easy chromatographic separations.