The Pummerer reaction involves the formation of an α-functionalized sulfide from a sulfoxide bearing at least one α-hydrogen atom. The reaction can also be described as an internal redox process where the SX group is reduced and the α carbon is oxidized.
The first report by Pummerer on the reaction which now bears his name appeared in 1909 and described the formation of thiophenol and glyoxylic acid on heating phenylsulfinylacetic acid with mineral acids. The products Pummerer observed resulted from hydrolysis of the initially formed α-substituted sulfides, which are the typical products of the reaction. The term “Pummerer reaction” was later extended to the reaction of sulfoxides with acid anhydrides.
Selenium and nitrogen analogs undergo similar reactions. The former is known as the seleno–Pummerer reaction, and the latter is usually referred to as the Polonovski reaction. The sila–Pummerer reaction, which is also discussed in this chapter, is the rearrangement of sulfoxides bearing a silyl group on the α carbon.
From a mechanistic point of view there are many other reactions, sometimes given specific names, such as the Sommelet–Hauser, Stevens, and Vilsmeier rearrangements, that appear to resemble the Pummerer reaction. Reactions in which the sulfoxide group acts as an oxidant in an intermolecular redox process have characteristics similar to the typical Pummerer reaction. The α-halogenation of sulfides, in which the sulfide sulfur may first be oxidized to a halosulfonium salt that rearranges to the final product, is formally similar to the Pummerer reaction.
For the sake of clarity and to be as exhaustive as possible, we have limited the scope of this chapter to the restrictive definition.