Pummerer rearrangement

What is Pummerer rearrangement?

The transformation of a sulfoxide bearing an α-proton to α-substituted sulfide can be achieved through an acid or acyclic anhydride-promoted reaction, as reported by Pummerer in 1909. This reaction involves the formation of a sulfenium (or thionium) intermediate and can also result in the reduction of sulfonium sulfur with concomitant oxidation or substitution at the α-carbon of sulfonium. It is commonly referred to as the Pummerer rearrangement or Pummerer reaction, and is sometimes used to form heterocycles via the addition of an intramolecular nucleophile to the sulfenium intermediate.

However, when nucleophiles other than those derived from the anhydride are present, the reaction can result in different forms of functionalization.

Pummerer rearrangement - general reaction scheme - Pummerer reaction
Pummerer rearrangement

Several promoters can be used to activate the Pummerer rearrangement, including HCl, acyclic anhydrides, p-toluenesulfonic acid, ZnCI2, TMSOTf, DAST (diethylaminosulfur trifluoride), and Me3SiX. In some cases, the reaction can occur under thermal conditions without promoters, although zeolite may be necessary to suppress it. The electrophilic nature of the sulfenium (or sulfonium) intermediate formed in this reaction allows it to react with even weak nucleophiles such as xylene and anisole.