Gem-difluorination in superacid: The dramatic role of halonium ions

In HF/SbF5, in the presence of CCl4 or NBS, unsaturated or hydroxylated piperidines yield difluoroanalogues in good yields. The ability to perform hydride abstraction on chloroderivatives, and the ability to form bridged bromonium ions from unsaturated substrates seem to completely influence the reaction course. Some aspects of the mechanism were clarified by DFT calculations.

In HF/SbF5, in the presence of CCl4 or NBS, unsaturated or hydroxylated piperidines yield difluoroanalogues in good yields. The ability to perform hydride abstraction on chloroderivatives, and the ability to form bridged bromonium ions from unsaturated substrates seem to completely influence the reaction course. Some aspects of the mechanism were clarified by DFT calculations.Figure optionsDownload as PowerPoint slide