Bismuth(III) trifluoromethanesulfonate: A chameleon catalyst for the Friedel-Crafts acylation

A mechanism for acylations catalyzed by bismuth(nl) triflate (1) is propose d in the case of the benzoylation of benzene, toluene, and chlorobenzene. W ith Bz(2)O as a reagent, 1 acts as a Lewis acid and allows the benzoylation of toluene. It is almost completely recovered after the reaction. With BzC l, 1 promotes an exchange reaction which generates BzOTf, which is the acti ve species of the benzoylation. In this latter case, the reaction leads to the formation of TfOH which finally reacts with BiCl3 to partially regenera te 1. The power of the Bz(2)O/1 system is less than that of BzCl/1, which a llows not only the benzoylation of toluene but also that of benzene and dea ctivated chlorobenzene. The activity of 1 is much higher than that of other metallic triflates previously reported, and is comparable with that of TfO H, however it also has the advantage that the triflate moieties are more ea sily recoverable.