Rearrangement of Allylic Sulfoxides. Selenoxides and Amine Oxides

The rearrangements of allylic sulfoxides, selenoxides, and amine oxides are an example of the first type. Allylic sulfonium ylides and ammonium ylides also undergo [2,3]-sigmatropic rearrangements. Rearrangements of carbanions of allylic ethers are the major example of the anionic type. These reactions are considered in the following sections. 

Rearrangement of Allylic Sulfoxides, Selenoxides, and Amine Oxides 

The rearrangement of allylic sulfoxides to allylic sulfenates was first studied in connection with the mechanism of racemization of allyl aryl sulfoxides.272 Although the allyl sulfoxide structure is strongly favored at equilibrium, rearrangement through the achiral allyl sulfenate provides a low-energy pathway for racemization. 

Concerted. Cycloadditions, Unimolecular Rearrangements, and Thermal Eliminations 

The reactions occur preferentially though an endo TS in which the sulfur substituent is oriented toward the allylic group.273 Computational studies (MP2/6-31G ) found the endo TS to be favored over the exo by 1.5-2.2. kcal/mol.274 

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