Catalytic difluorination of olefins achieved

By uniting several pieces of known chemistry, István Gábor Molnár and Ryan Gilmour of the University of Münster have devised a method for the elusive catalytic vicinal difluorination of terminal olefins (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b01183). Chemists have come up with myriad strategies for using fluorine to modulate the structure and function of organic molecules used as pharmaceuticals and agricultural chemicals and in electronic materials—but a few gaps remain. For example, direct catalytic dihalogenation of unactivated olefins has been developed for chlorine and bromine but not for fluorine. As Molnár and Gilmour explain, the limitation has been identifying a suitable catalyst that goes beyond producing monofluorinated or geminal difluorinated products. Building on fluorination tricks developed by others, the Münster team combined catalytic p-iodotoluene, amine•HF reagents as a fluorine source, and Selectfluor as an oxidizing agent to create an in situ hypervalent difluorination reagent (shown). The researchers showed that the catalyst is selective for vicinal difluorinations in air at room temperature in the presence of sensitive groups such as alcohols and tosylates. They also demonstrated a preliminary asymmetric difluorination, which helps address the lack of enantioselective olefin dihalogenations.