Electrochemical Synthesis of γ-Lactams from Amides and Alkenyl Trifluoroborates by [3 + 2] Annulation

Electrochemical [3 + 2] annulation of amides with alkenyl trifluoroborates has been achieved, using diphenyl sulfide as the mediator. This electrochemical method requires no base or external chemical oxidant and provides facile access to structurally diverse γ-lactams from readily available starting materials. Preliminary mechanistic studies show that the electrogenerated vinyl diphenylsulfonium salt is the key intermediate to facilitate the [3 + 2] annulation.