Trifunctionalization of Cinnamyl Alcohols Provides Access to Brominated α,α-Difluoro-γ-lactones via a Photoinduced Radical–Polar–Radical Mechanism

A photochemical synthesis of brominated α,α-difluoro-γ-lactones from cinnamyl alcohols and ethyl bromodifluoroacetate is reported via one-pot Giese addition/lactonization/halogen-atom transfer (XAT) processes. This transformation provides brominated α,α-difluoro-γ-lactones in moderate to good diastereoselectivities. The reaction affords a rapid increase in molecular complexity in organofluorine chemical space. Dispersion-corrected density functional theory (DFT) calculations and experiments support a lactonization-induced radical chain mechanism in which a long-lived radical intermediate undergoes a diastereoselective halogen-atom transfer to restart the radical chain cycle.