Copper-catalyzed aerobic intramolecular dehydrogenative cyclization of N,N-disubstituted hydrazones through C(sp(3)-H functionalization.

An aerobic activity: The title reaction proceeds through an oxidation/cyclization/aromatization sequence under an atmosphere of O(2) (see scheme; DBU=1,8-diazabicyclo[5.4.0]undec-7-ene, DCE=1,2-dichloroethane, DMS=dimethylsulfide). This coupling reaction is the first to proceed via an iminium intermediate for a C(sp(3)-H bond-functionalization process, and provides an environmentally friendly and atom-efficient access to substituted pyrazoles.