Cu-catalyzed cascade difluoroalkylation/5- endo cyclization/β-fluorine cleavage of ynones.

A copper-catalyzed, redox-neutral cascade difluoroalkylation/5- endo annulation/β-fluorine cleavage of ynones is developed, providing a direct and stereoselective method to access synthetically important α-monofluoroalkenyl cyclopentanones. Mechanistic studies suggest an unprecedented Cu II -assisted β-fluorine fragmentation, which may be valuable for the challenging but important C-F bond activation. Moreover, the in situ generated difluorocarbene was found to serve as an effective reductant for the regeneration of copper(I) catalyst, thus avoiding the addition of external reductants.