Catalytic HF Shuttling between Fluoroalkanes and Alkynes

In this paper we report a catalytic method to transfer formal equivalents of HF from fluoroalkanes to an alkyne. The method leads to a simple and sustainable approach to generate difluoroalkanes and tolerates numerous sensitive functional groups including halogen, protected amine, ester and thiophene substituents. BF3-OEt2 catalyses this new catalytic transformation. Mechanistic studies (DFT, probe experiments) suggest the catalyst is intimately involved in both the defluorination and fluorination steps required for HF transfer, with BF3 acting as a Lewis acid and OEt2 a weak Lewis base that mediates proton transfer. Fluoroalkenes are demonstrated as competent intermediates and their conversion to difluoroalkanes was found to be reversible. These results establish the first true HF shuttle process (i.e. bidirectional) and represent a potentially powerful method for recycling fluorocarbons