N-Heterocyclic Carbene-Photocatalyzed Tricomponent Regioselective 1,2-Diacylation of Alkenes Illuminates the Mechanistic Details of the Electron Donor-Acceptor Complex-Mediated Radical Relay Processes

Progress in the development of photocatalytic reactions requires a detailed understanding of the mechanisms underpinning the observed reactivity, yet mechanistic details of many photocatalytic systems, especially those that involve electron donor-acceptor complexes, have remained elusive. We report herein the development and a combined mechanistic and computational study of photocatalytic alkene 1,2-diacylation that enables a regioselective installation of two different acyl groups, establishing direct, tricomponent access to 1,4-diketones, key intermediates in heterocyclic and medicinal chemistry. The studies revealed the central role of the electron donor-acceptor complex formed from an N-heterocyclic carbene (NHC) catalyst-derived intermediate and an acyl transfer reagent, providing a detailed description of the structural and electronic factors determining the characteristics of the photoinduced charge-transfer process that mediates photocatalytic transformation. The in-depth investigation also illuminated the roles of other radical intermediates and electron donors relevant to the catalytic activities of N-heterocyclic carbenes in radical reactions.

Automated summary

Progress in developing photocatalytic reactions requires a detailed understanding of the underlying mechanisms, especially those involving electron donor-acceptor complexes. This study reports a new method for regioselective installation of two different acyl groups through photocatalytic alkene 1,2-diacylation. The research highlights the central role of electron donor-acceptor complexes in mediating the photoinduced charge transfer process and sheds light on the catalytic activities of N-heterocyclic carbenes in radical reactions.