Catalyst-Free and Oxidant-Free Synthesis of 1,3,5-Trisubstituted Pyrazoles by Michael-Type Addition of Hydrazone sp2 Nitrogen Atoms to Enones

Abstract

A new single-step approach to 1,3,5-trisubstituted pyrazoles from hydrazones and α,β-unsaturated keto esters has been developed. This catalyst- and oxidant-free transformation involves a Michael-type addition of the hydrazone sp² nitrogen to the enone and a redox isomerization. The procedure has a wide substrate scope and shows good compatibility with both α-ester- and α-keto-substituted hydrazones.