Trifunctionalization of Cinnamyl Alcohols Provides Access to Brominated alpha,alpha-Difluoro-gamma-lactones via a Photoinduced Radical-Polar-Radical Mechanism

A photochemical synthesis of brominated alpha,alpha-difluoro-gamma-lactones from cinnamyl alcohols and ethyl bromodi-fluoroacetate is reported via one-pot Giese addition/lactonization/halogen-atom transfer (XAT) processes. This transformation provides brominated alpha,alpha-difluoro-gamma-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.