Sulfonium YlideEnabled, Copper-Catalyzed Difluoromethylation,Monofluoromethylation, and Monofluoroalkylation of Lithium Aryl ^<i>n</i>Butyl Borates

A copper-catalyzed fluoroalkylation of lithium aryl ^<i>n</i>butyl borates with electrophilic fluoroalkylating reagent YlideFluor for the preparation of di-, trifluoromethyl-, and monofluoroalkyl-substituted (hetero)arenes under mild conditions was described. Control experiments indicated that a fluoroalkyl radical, rather than a difluorocarbene intermediate, is involved in the catalytic process. In addition, stoichiometric reactions demonstrated that transmetalation of copper catalyst with lithium aryl ^<i>n</i>butyl borate takes place before the single-electron-transfer (SET) oxidation of an ate-type Cu(I) intermediate [Cu^I(Ar)(SCN)]⁻ by YlideFluor. Based on these mechanistic results, a reasonable catalytic cycle for the copper-catalyzed fluoroalkylation of lithium aryl ^<i>n</i>butyl borates was proposed.