Perdefluorinative borylation of perfluoroalkyl and gem-difluoroalkenes

Polyfluorinated organic molecules including perfluoroalkyl substances (so-called PFAS) are broadly used as water-repellents and flame retardants, in paper coatings, fire extinguishing chemicals, agrochemicals, and drugs. However, these compounds are resistant towards degradation and known to bioaccumulate in the environment and organ tissue with numerous associated negative health effects. This persistence further renders the chemical treatment of PFAS highly challenging. We herein report a “zipper” reaction that strips off all fluorine atoms from a perfluoroalkyls bound to an alkene and converts these PFAS compounds into synthetically useful boronate building blocks without destruction of the carbon framework. This is achieved by a combination of pinacolborane and lithium methoxide that iteratively removes the fluoride substituents from the attached perfluoroalkyl chain through repeated hydroboration/β-F-elimination steps. The reaction then installs a boronate function at the chain terminus, which overall turns the problematic PFAS into useful synthesis reagents. Yields of up to >99% are achieved per fluorine atom and the isolation of LiF by simple filtration is demonstrated. The reaction also works on gem -difluoroalkenes, which we conclude to be intermediates of the PFAS perdefluoro-monoborylation reaction.