Sulfur participation in [3,3]-sigmatropic rearrangements

The thio-Claisen rearrangement is a general and facile process that is often advantageous over the standard Claisen rearrangement. Several asymmetric variants of the thio-Claisen rearrangement have been reported. The rearrangement of sulfonium salts and sulfoxides takes place even more readily. Alkenyl sulfoxides and sulfilimines undergo a highly stereo controlled cyclization to lactones and lactams, respectively, upon reaction with haloketenes; this synthetically useful process entails a [3,3]-sigmatropic rearrangement of a zwitterionic intermediate. Sulfur-containing functionalities located at the periphery of the Claisen substrates exert a powerful influence on the outcome of the process.