Synthesis of 4-Chalcogenyl Pyrazoles via Electrophilic Chalcogenation/Cyclization of alfa,beta-Alkynic Hydrazones

A facile method for the synthesis of 4-chalcogenylated pyrazoles has been developed via electrophilic chalcogenation/cyclization of alfa,beta-alkynic hydrazones. The cyclization of alfa,beta-alkynic aldehyde hydrazones could be induced by using either sulfenyl chloride or the S-electrophiles generated in situ from the reaction of NCS and arythiol. The developed method was successfully applied to the synthesis of the sulfenyl analogue of Celecoxib.