Deoxyfluorinations continue to evolve

Once upon a time, carrying out a deoxyfluorination reaction to replace an alcohol group with fluorine required using brutish reagents such as sulfur tetrafluoride gas or the sulfur fluoride-based liquids DAST or Deoxo-Fluor. In time, chemists have developed milder crystalline reagents, such as XtalFluor, Fluolead, PhenoFluor, and PyFluor. While the solid reagents are easier to handle, the compounds each have limitations, including low thermal and moisture stability, poor functional group selectivity, and the need for an auxiliary reagent such as a base. Researchers led by Tobias Ritter of Harvard University and the Max Plank Institute for Kohlenforschung have now reported a new reagent, called AlkylFluor, that resolves many of the problems (Org. Lett. 2016, DOI: 10.1021/acs.orglett.6b03086). Ritter’s group initially developed PhenoFluor, a difluoroimidazoline reagent, which works well for deoxyfluorination of phenols and aliphatic alcohols but is sensitive to moisture and requires special handing. The researchers subsequently made an imidazolium chloride derivative, PhenoFluorMix, which is stable in air but limited to arene deoxyfluorinations. AlkylFluor is a monofluoroimidazolium borate derivative that’s stable to air and moisture and geared toward deoxyfluorination of primary and secondary aliphatic alcohols. Using the deoxyfluorination of testosterone as a test case, the researchers found that AlkylFluor outperformed other reagents.