Catalytic HF Shuttling between Fluoroalkanes and Alkynes

In this paper, we report BF3 & sdot; OEt2 as a catalyst to shuttle equivalents of HF from a fluoroalkane to an alkyne. Reactions of terminal and internal aliphatic alkynes led to formation of difluoroalkane products, while diarylalkynes can be selectively converted into fluoroalkenes. The method tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. Mechanistic studies (DFT, probe experiments) suggest the catalyst is involved in both the defluorination and fluorination steps, with BF3 acting as a Lewis acid and OEt2 a weak Lewis base that mediates proton transfer. In certain cases, the interconversion of fluoroalkene and difluoroalkane products was found to be reversible. The new catalytic system was applied to demonstrate proof-of-concept recycling of poly(vinylidene difluoride). A catalytic method to transfer formal equivalents of HF from fluoroalkanes to an alkyne is reported. The method leads to a simple approach generating geminal difluoroalkanes and it tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. Poly(vinylidene difluoride) (PVDF) was shown to act as an HF donor in place of the fluoroalkane.**+image