Transition from π radicals to σ radicals: substituent-tuned cyclization of hydrazonyl radicals

Angew Chem Int Ed Engl. 2014 Mar 17;53(12):3158-62. doi: 10.1002/anie.201309918.

Abstract

Hydrazonyl radicals are known for their p-electronic structures; however, their s-electronic structures have not been reported as yet. Herein, we show that readily accessible b,g- and g,d-unsaturated N-trichloroacetyl and Ntrifluoroacetyl hydrazones can be conveniently converted into hydrazonyl s radicals, which subsequently undergo 5-exo-trig radical cyclization at the N1 or N2 atom to form pyrazolines and azomethine imines, respectively.