Synthesis of trifluoromethylated pyrazolidines by [3+2] cycloaddition

A highly efficient [3 + 2] cycloaddition between trifluoromethylated N-acylhydrazones and nitroolefins in the presence of potassium hydroxide under phase transfer catalysis is developed to afford potentially bio-active trifluoromethylated pyrazolidines, which can be further transformed into trifluoromethylated pyrazoles in good yields.