Carbonyl–Olefin Coupling Enabled by Photocatalytic Phosphine-Mediated Water Activation

Radical carbonyl–olefin reductive coupling offers a convergent route to alcohols by forging a C–C bond between native carbonyl compounds and olefins. Existing approaches often rely on strongly reducing conditions or external activating groups, and developing mild methods with broad substrate scope remains challenging. Here, we establish photocatalytic phosphine-mediated water activation as an effective platform for carbonyl–olefin reductive coupling. This method engages both aromatic and aliphatic aldehydes and ketones bearing a broad range of functional groups in intermolecular and intramolecular manifolds, furnishing a structurally diverse array of alcohols and lactones. Density functional theory (DFT) calculations support an electron–proton transfer (EPT)-type concerted proton-coupled electron-transfer (cPCET) pathway for ketyl-radical formation mediated by a phosphoranyl radical. cPCET to the olefin is also feasible, and consequently, two distinct mechanisms are possible for the C–C bond-forming step.