Highly Enantioselective Synthesis of Monofluoroalkenes by Rhodium-Catalyzed Asymmetric Arylation/Defluorination of Allyl Difluorides

The reaction of readily available E -allyl difluorides (R 1 CH = CHCF 2 COR 2 ) containing a CF 2 COR 2 moiety with arylboronic acids catalyzed by a chiral diene-rhodium complex gives high yields of chiral monofluoroalkenes (R 1 ArC*HCH = CFCOR 2 ) with perfect enantioselectivity (enantiomeric excess (ee) of > 99% in all cases) and high level of Z / E selectivity (up to 20:1). The reaction is proposed to proceed through enantioselective arylrhodation of the E -allyl difluorides forming a β,β-difluoroalkylrhodium intermediate, followed by stereoselective β-fluoride elimination. The CF 2 COR 2 moiety plays a key role in activating the E -allyl difluorides toward arylrhodation/defluorination in executing the catalytic cycle, and it serves as a handle for further functionalization.