Direct and Enantioselective Synthesis of N−H‐Free 1,5‐Benzodiazepin‐2‐ones by an N‐Heterocyclic Carbene Catalyzed [3+4] Annulation Reaction

An NHC‐catalyzed formal [3+4] annulation of α,β‐unsaturated acylazoliums with protecting‐group‐free aryl 1,2‐diamines was developed for a direct and highly enantioselective 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. Get selective! An N‐heterocyclic carbene catalyzed formal [3+4] annulation of α,β‐unsaturated acylazoliums with protecting‐group‐free aryl 1,2‐diamines was developed for a direct and highly enantioselective synthesis of 4‐aryl N−H‐free 1,5‐benzodiazepin‐2‐ones (see scheme).