Perfluoroalkylcopper compounds [FFCU], when they react with 1-bromo-1- perfluoroalkylethylenes 1, do not give the expected gem-disubstituted compounds 3, but the vic-disubstituted products 2 in 60–70% yields. These results show that the reaction does not proceed through a simple vinylic substitution. 1H and 19F NMR data are given for the new compounds.
