A Facile Synthesis of CF3-Substituted Pyrazolidines and Pyrazolines

A Lewis acid-catalyzed [3+2] cycloaddition of trifluoromethylated N-acylhydrazones with alkenes was explored, and a series of CF3-substituted pryazolidines were obtained in high yields (up to 91%). The reaction features the use of cheap and readily available trifluoromethylated N-acylhydrazones as trifluoromethyl building blocks, mild reaction conditions and easy operation. Furthermore, the cycloadducts can be transformed into trifluoromethylated pyrazolines in excellent yields.