Copper-Catalyzed Defluorinative Coupling of gem-Difluoroallenes with Grignard Reagents

gem-Difluoroallenes undergo copper-catalyzed defluorinative coupling with alkyl and aryl Grignard reagents to give monofluoroallenes. Using Cu(OAc)2 (10 mol%) in THF at −20 °C, eleven products are obtained in 64–95% isolated yield. The transformation replaces one fluorine atom while retaining the cumulated diene. Catalyst screening and substrate scope are described, together with a tentative carbocupration/β-fluoride-elimination pathway.