Direct Cyclization/Chlorination Strategy of Hydrazines for Synthesis of 4-Chloropyrazoles by TCCA

A new method for synthesis of various 4-chloropyrazoles through the direct cyclization/chlorination of hydrazines by using 1,3,5-trichloroisocyanuric acid (TCCA) as both oxidant and chlorinating agent under mild conditions has been proposed. Based on the detailed optimization of the reaction conditions, the substrate generality has been investigated, and the yields of the desired products are up to 92%.