gem-difluoroolefin synthesis: general methods via thermostable difluorovinylmetals starting from 2,2,2-trifluoroethanol derivatives

gem-Difluoroolefins with a wide range of substituents are readily synthesiz ed from commercially available 2,2,2-trifluoroethyl p-toluenesulfonate, via a pathway that comprises the following two processes: (i) a boron-mediated alkylation leading to gem-difluorovinylborane, and (ii) subsequent direct functionalizations via gem-difluorovinylcopper. This methodology provides a general one-pot synthesis of unsymmetrically disubstituted difluoroolefins by the introduction of difluorovinylidene unit as an ambiphile (CF2=C--(+) ). alpha-Nonsubstituted difluorovinylzirconocene and -zinc generated in sit u from 2,2-difluorovinyl p-toluenesulfonate opens a complementary way to th e synthesis of monosubstituted gem-difluoroolefins bearing unsaturated carb on substituents. These difluorovinylmetals (B, Cu, Zr, Zn) are all remarkab ly thermostable against beta-elimination in spite of the absence of electro n-withdrawing groups, and are therefore easy to handle and react readily. ( C) 2000 Elsevier Science S.A. All rights reserved.