Stereoselective Palladium-Catalyzed C-F Bond Alkynylation of Tetrasubstituted gem-Difluoroalkenes.

A stereoselective Pd(PPh 3 ) 4 -catalyzed C-F bond alkynylation of tetrasubstituted gem -difluoroalkenes with terminal alkynes has been developed. The method gives access to a great variety of conjugated monofluoroenynes bearing a tetrasubstituted alkene moiety with well-defined stereochemistry. Chelation-assisted oxidative addition of Pd to the C-F bond is proposed to account for the high level of stereocontrol. X-ray structure of a key monofluorovinyl Pd(II) intermediate has been obtained for the first time as evidence for the proposed mechanism.