Bismuth(III) Chloride and Triflate: Novel Catalysts for Acylation and Sulfonylation Reactions. Survey and Mechanistic Aspects

Abstract

Acylation and sulfonylation reactions catalyzed by bismuth(III) chloride or triflate are reviewed. For Friedel-Crafts reactions the mechanistic study reveals the different behavior of Bi(OTf)3, depending on the electrophilic agent used; either that of Lewis acid (with acid anhydrides) or that of procatalyst, carrier of triflate groups (with acid chlorides), leading to in situ generation of mixed anhydrides (RCOOTf or RSO2OTf) responsible for the aromatic electrophilic substitution. Among the metal triflates tested in these reactions, only Ga(III) and In(III) exhibit high activity. Bi(OTf)3 appears to be superior to other metal triflates known to catalyze the acylation of alcohols using acid anhydrides as reagents. BiCl3, especially in the presence of a metal iodide, is the only known efficient catalyst for acyldesilylation reactions of allyl- and enoxysilanes. The low cost of bismuth compounds and their low (or absence of) toxicity are emphasized.