Direct and Enantioselective Synthesis of N-H-Free 1,5-Benzodiazepin-2-ones via NHC-Catalyzed [3+4] Annulation Reaction.

An NHC-catalyzed formal [3+4] annulation of alpha,beta-unsaturated acylazoliums with protecting-group-free aryl 1,2-diamines was developed for a direct and highly enantio-selective synthesis of 4-aryl N-H-free 1,5-benzodiazepin-2-ones. This methodology offers an efficient and rapid access to a wide range of enantioenriched target compounds from easily accessible starting materials. The protocol is also scalable and the desired products can easily undergo subsequent N-functionalization to afford diverse N-substituted derivatives. Additionally, a mechanism was proposed to explain the high enantioselectivity in this process.