A novel double insertion of the difluoromethylene unit from trifluoromethylcopper into the carbon–copper bond of perfluoroaryl- and perfluorovinylcopper reagents: preparation, mechanism and applications of new fluorinated copper reagents

Abstract

Reaction of CF 3Cu with pentafluorophenylcopper, prepared from CuBr and pentafluorophenylcadmium C 6F 5CdX, gave the double CF 2 unit insertion product, C 6F 5CF 2CF 2Cu, in 70–80% yields. The insertion reaction also worked well with CF 3MX (M = Cd, Zn; X = Br, CF 3) and C 6F 5CdX in the presence of CuBr at room temperature to afford C 6F 5CF 2CF 2Cu. With a vinylcopper analog, ( Z)-CF 3CFCFCu, double CF 2 insertion also occurred resulting in the formation of ( E)-CF 3CFCFCF 2CF 2Cu, which could be trapped with allyl bromide to give ( E)-CF 3CFCFCF 2CF 2CH 2CHCH 2. When CF 2CFCu was used as a substrate, ( E)-CF 3CFCFCF 2CF 2Cu was observed, but in low yield. A mechanism for this novel double CF 2 insertion is proposed to involve a copper difluorocarbenoid complex intermediate, which inserted into the carbon–copper bond of the fluorinated phenyl and vinyl coppers to form fluorinated benzyl or allyl copper reagents. The intermediate benzyl or allyl coppers are more reactive than the pentafluorophenyl or vinylcoppers and rapidly undergo insertion of another CF 2 unit. Perfluorobenzylcopper was prepared independently and gave C 6F 5CF 2CF 2Cu on reaction with CF 3Cu. The resultant new copper reagent, such as C 6F 5CF 2CF 2Cu, showed good thermal stability and reactivity. Halogenation of the copper reagent gave the corresponding halides C 6F 5CF 2CF 2X, and insertion of sulfur dioxide into the carbon–copper bond followed by trapping with allyl halide gave the corresponding allylic sulfones. C 6F 5CF 2CF 2Cu also participated in coupling reactions with allyl halides, vinyl halides and aryl halides to give the coupled products in good yields. Selective functionalization of both aryl rings of the fluorinated diarylethanes with a variety of reagents has also been demonstrated.