Electrochemical Intermolecular Benzylic C(sp³)-H Imidation via Bromide-Mediated Cross-Dehydrogenative Coupling

Electrochemical benzylic C(sp³)-H/N-H cross-coupling represents a green, sustainable, and straightforward strategy to construct benzylic C(sp³)-N bonds. Herein, a direct electrochemical intermolecular benzylic C(sp³)-H imidation of diarylmethanes and alkylarenes with N-acylsulfonamides or sulfonimides is described, which proceeds in an undivided cell under transition-metal- and external-oxidant-free conditions. This methodology does not require prefunctionalized reagents and utilizes readily available and cost-effective sodium bromide as both a mediator and a supporting electrolyte. The cross-coupling strategy shows good tolerance to a diverse array of diarylmethanes, alkylarenes, N-acylsulfonamides, and sulfonimides, enabling selective benzylic C-H imidation of both primary and secondary benzylic C(sp³)-H bonds. The synthetic potential of this approach has been substantiated through successful scale-up reactions, product derivatizations, and late-stage functionalization of bioactive molecules and pharmaceuticals. Based on comprehensive mechanistic experiments and cyclic voltammetry studies, a mechanism involving bromine-mediated formation of an N-bromo-imidyl species is proposed. The N-bromo species is supposed to undergo N-Br bond homolysis to generate a nitrogen-centered imidyl radical, which would facilitate intermolecular benzylic C(sp³)-H imidation through a hydrogen atom transfer pathway.