An efficient copper(I)-catalyzed synthesis of 1,3,5-trisubstituted pyrazoles from N-arylhydrazonoyl chlorides and terminal alkynes is developed. N-arylhydrazonoyl chlorides are obtained from anilines by diazotization followed by condensation with 2-chloro-1,3-dicarbonyl compounds. The process is experimentally simple and provides pyrazole products in good to excellent yields. The reaction appears to proceed via a step-wise mechanism: addition of in situ formed copper acetylides to hydrazonoyl chlorides, followed by cyclization.

Scope, limitations, and mechanistic considerations will be discussed in the presentation.