Copper(I)-only catalyzed reactions of (E)-2,3-difluoro-3-stannylacrylic ester with acid chlorides and mechanistic studies of the "copper effect" in stille coupling reactions.

[reaction: see text] The reactions of (E)-2,3-difluoro-3-stannylacrylic ester with acid chlorides under catalysis of CuI stereospecifically afforded ethyl (2Z)-2,3-difluoro-4-oxo-substituted 2-butenoates in good yields. Moreover, direct spectroscopic observation of the corresponding organocopper reagent was observed for the first time in Stille coupling reactions of organostannanes.