Practical synthesis of pyrazoles via a copper-catalyzed relay oxidation strategy

Abstract

Various 1,3- and 1,3,4-substituted pyrazoles are smoothly formed via copper-catalyzed cascade reactions of oxime acetates, amines and aldehydes. This relay oxidative process involves copper-promoted N–O bond cleavage and C–C/C–N/N–N bond formations to furnish pyrazolines, and sequential Cu–O₂ system-involved oxidative dehydrogenation of pyrazolines to afford pyrazoles. This transformation provides a novel and versatile approach for the synthesis of pyrazoles, with an inexpensive copper catalyst and green oxidants. It is atom- and step-economical, and possesses a good functional group tolerance, as well as operational simplicity.