Pummerer rearrangement

The Pummerer Rearrangement

The Pummerer rearrangement is a chemical reaction that occurs when alkyl sulfoxide reacts with acetic anhydride. In this reaction, alkyl sulfoxide undergoes a transformation from a sulfoxide to a thioether.

Mechanisms

The kinetic and thermodynamic data suggest that the F - O transition is coupled with the pumping of one proton. Since one H+ is pumped for each electron, one proton must be pumped from somewhere else. Mutant analysis and structural data are useful tools to speculate about the pumping mechanism.

One mechanism for pumping a proton is based on the consistency principle. The structure of the pumper is depicted as a pentameric hydrogen bond network with the channel opening direction represented by a cleft. The color red indicates the active consistency-breaking site. Blue indicates changes satisfying the consistency principle.

Substrates

Substrates for Pummerer rearrection are organic molecules that contain a thiol group. During the reaction, the thiol is replaced by an a-hydroxysulfide group. Consequently, this transformation yields a methylthiomethyl ester, which is a useful product.

Alkyl sulfoxide is an ideal substrate for this rearrangement. The thionium ion produced by the reaction is attacked by a nucleophile. Activators commonly used in the reaction include acetic anhydride, trifluoroacetic anhydride, and trifluororomethanesulfonic anhydride.

Products

The Pumperer rearrangement is a transformation of a hydrocarbon ring in organic compounds. There are several proposed mechanisms for this transformation. One mechanism involves protonation of the sulfoxide atom in olefin 1. This intermediate undergoes dehydration and forms the acetate anion D. During the rehydration step, the sulfonium ion E undergoes protonation at an electrophilic ethylidene carbon atom. The resulting product G is a tertiary carbocation with an a-hydroxysulfide group. The authors noted that further studies are needed to understand this transformation.

Another mechanism for the Pumperer rearrangement is the elimination of hydrogen halides. This process can be employed to prepare 3-thiosubstituted a, b-unsaturated ketones. Another way to achieve the rearrangement is to remove hydrogen halides from enol ethers by using CAN in DMF. In addition, ring-opening reactions of cyclobutenes with a thioether in the 3-position have been used to prepare 2,4-dienes. Using this approach, high yields of medium-ring dienes have been achieved. Moreover, the 2-alkylation of a functionalized alkyne affords b-alkyl-b-phenylthio-a,b-unsaturated ketones.

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