Palladium-Catalyzed Photoredox [3 + 2+1]/[2 + 2] Annulation of 1,4-Enynyl Acetates with Allylamines and CO via Energy Transfer

Abstract Photoinduced palladium catalysis has become a promising synthetic technology for innovating new tool boxes for constructing complex structural scaffolds that are challenging to install by traditional methods. However, strategies for homolysis of the inherent C–X bonds (X = heteroatom) by the photoinduced palladium catalysis to allow their transformations have yet been unexplored. Herein, we disclose a visible-light-induced palladium-catalyzed photoredox [3 + 2+1]/[2 + 2] annulation of 1,4-enynyl acetates with allylamines and CO via radical-polar crossover (RPC) and energy transfer (EnT) for the synthesis of 3-azabicyclo[4.2.0]-oct-5-en-4-ones. This reaction features high diastereoselectivity and broad functional group tolerance. Mechanistically, 1,4-enynyl acetates directly undergo homolysis of the C–O bonds initiated by photoinduced palladium catalysis to form the hybrid alkyl Pd(I)-radical species and then the transposed propargyl Pd(I)-radical species and the hybrid allenyl Pd(I)-radical complex, enabling access to 3-azabicyclo-[4.2.0]-oct-5-en-4-ones via RPC and EnT.