Olefins Easily Flagged With Fluorine

Organofluorine chemistry has been flourishing during the past decade, with new and improved synthetic methods being reported one after the other. One of the remaining challenges has been designing methods for direct carbon-fluorine bond formation which don’t require extra steps to prefunctionalize the starting material so that it more readily undergoes fluorination. To that end, Princeton University’s Marie-Gabrielle Braun and Abigail G. Doyle have developed a direct catalytic method for allylic C–H fluorinations (J. Am. Chem. Soc. 2013, DOI: 10.1021/ja407223g). The researchers prepare allylic fluorides from simple olefins by using a palladium sulfoxide-chromium salen cocatalyst system, with (CH₃CH₂)₃N•3HF as an inexpensive nucleophilic fluorine source. The reaction provides moderate yields and high selectivity for a variety of branched allylic fluorides. The ability to easily convert C–H directly to C–F in olefins should aid discovery and manufacture of pharmaceuticals, structural materials, and small-molecule tracers for positron emission tomography, the researchers note. For example, they show that the reaction can be applied to late-stage functionalization of drug candidates by adding fluorine to a steroid.