Photoredox-catalyzed α-Scission vs β-Scission of PR3-OH Radicals: Synthetic Utilizations and Mechanistic Studies

Photoinduced generation of phosphoranyl radicals offers a versatile strategy to access a variety of synthetically valuable radicals, which has opened exciting new opportunities for radical manipulations and synthetic chemistry. While β-scission mode of phosphoranyl radicals has been intensively studied and broadly utilized via deoxygenation or desulfurization processes, a long-standing challenge still remains in the regulation of phosphoranyl radical to undergo α-scission pathway by overcoming the inherent driving force to generate the stable phosphine oxide via β-scission, which has been largely unexplored and rarely applied. We herein developed an unprecedented protocol to switch the fragmentation patterns between α- and β- scission of the generated phosphoranyl radicals under photocatalytic conditions. The success of our strategy presumably relies on finely tuning the reactivity of the crucial P(OH)R3 radical by altering the R substituents, and this P(OH)R3 radical intermediate is ultimately from water and tertiary phosphine reagent. Notably, the synthetic utility of both fragmentation patterns of the P(OH)R3 radical were well demonstrated via selective hydroalkylation or hydrogenation transformations of alkenes. A combination of experimental and computational studies was carried out to understand the reaction mechanisms.