Alkoxy sulfuranes

The displacement of both alkoxy groups at sulfur in 239 with predominant inversion of configuration can be explained by the simultaneous formation of two different intermediates (or transition states) 242 and 243, which undergo decomposition before pseudorotation. In this context, it is interesting to note that the formation and decomposition of only one such sulfurane intermediate would give two sulfinate products with inverted and retained configuration at sulfur. 

Analogous chemistry was observed by Denney and co-workers11 when divalent sulfur nucleophiles were allowed to react with dioxetanes. Thus, diphenyl sulfide gave epoxide and diphenyl sulfoxide, presumably via the sulfurane (63), as shown in Eq. (50). When the ligands on the sulfur nucleophile were alkoxy groups, NMR evidence for the intermediary sulfuranes was provided. Similar results were observed by Wasserman... 

Alkoxysulfonium salts are cleaved by bromide and iodide ions (145) to sulfoxides with retained configurations indicating a Sn2(C) displacement at alkoxy carbon by the soft nucleophiles. The use of equimolar chloride ion leads to a mixture of sulfides and partially racemized sulfoxides. The intervention of sulfurane intermediates has been postulated (146, 147) for the reaction. 

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