Excited-State Copper-Catalyzed [4+1] Annulation Reaction Enables Modular Synthesis of α,β-Unsaturated-γ-Lactams

Synthesis of alpha ,fi-unsaturated-gamma-lactams continue to attract attention due to the importance of this structural motif in organic chemistry. Herein, we report the development of a visible -light-induced excited-state copper-catalyzed [4 + 1] annulation reaction for the preparation of a wide range of gamma-H, -OH, and -OR-substituted alpha ,fi-unsaturated-gamma-lactams using acrylamides as the 4-atom unit and aroyl chlorides as the 1-atom unit. This modular synthetic protocol features mild reaction conditions, broad substrate scope, and high functional group tolerance. The reaction is amenable to late-stage diversification of complex molecular architectures, including derivatives of marketed drugs. The products of the reaction can serve as versatile building blocks for further derivatization. Preliminary mechanistic studies suggest an inner-sphere catalytic cycle involving photoexcitation of the Cu(BINAP) catalyst, single-electron transfer, and capture of radical intermediates by copper species, followed by reductive elimination or protonation to give the desired gamma-functionalized alpha ,fi- unsaturated-gamma-lactams.