[3+2] Cycloaddition of Trifluoromethylated N-Acylhydrazones with Maleates: Synthesis of Trifluoromethylated Pyrazolidines

An efficient [3+2] cycloaddition reaction of trifluoromethylated N-acylhydrazones with dimethyl maleate has been developed under basic conditions. This protocol provides an easy access to potentially bioactive trifluoromethylated pyrazolidines in moderate to excellent yields. It also illustrates that the trifluoromethylated N-acylhydrazones are useful trifluoromethyl building blocks for the synthesis of trifluoromethylated N-heterocycles.