Faster initiation in the Friedel-Crafts reaction of benzyl fluorides using trifluoroacetic acid as activator

We report that the addition of a catalytic amount of trifluoroacetic acid (TFA) shortens the induction period associated with the 1,1,1,3,3,3-hexafluoroisopropoanol (HFIP)-promoted Friedel-Crafts reaction of benzylic fluorides. This faster initiation is due to TFA’s strong hydrogen-bond donation capability, not its Bronsted acidity. The improved reaction conditions were applied to a set of substrates, demonstrating how they could improve yields and reliability of this transformation.