Rearrangements of sulfoxides

Rearrangement of sulfoxides 38a, b exhibited the interplay of several conformational factors. Both diastereomers afford predominant axial (trans) alcohol, but with opposite absolute configuration. The (R, R)-diastereomer strongly prefers the exo-transition state, whereas the (R, S)-isomer prefers the endo conformation. Hoffmann interprets these results in terms of an approximately 3-fold preference for the exo-transition state but a 6-fold preference for formation of an axial bond, these effects reinforcing each other in one isomer but opposing each other in the second. 

Analogous with the rearrangement of allylic sulfoxides is the [2,3]-sigmatropic rearrangement of propargylic sulfoxides to allenic sulfenates. This process, which has been relatively little studied so far, appears to be the first step in the facile and quantitative rearrangement of sulfoxide 98 to the hemithioacetal 101 (equation 45)167. This reaction,... 

III. REARRANGEMENTS OF SULFOXIDES TO SULFENATES A. Thermal and Ionic Rearrangements... 

Mislow s [2,3]-sigmatropic rearrangement of sulfoxides is more than a mechanistic curiosity, because the intermediate sulfenate 5.83 can be intercepted by a suitably thiophilic reagent, converting an enantiomerically enriched sulfoxide 5.82 into a comparably enriched rearranged allyl alcohol 5.84, with suprafacial shift 5.85 of the functionality. 

This reagent is both a Lewis acid and a dehydrating agent. Thus it effects Pummerer rearrangement of sulfoxides and rearrangement of pinacol to pinacolone via an epoxide.2... 

Having read Chapter 36, you should be able to classify the pericyclic rearrangement reaction it is a [2,3]-sigmatropic rearrangement (make sure you can see why before you read further) and as such is the first of the pericyclic rearrangements of sulfoxides that we shall talk about. 

The Pummerer rearrangement of sulfoxides with acid anhydrides has been extensively utilized as a method for the synthesis of a-substituted sulfides. When a,(3-unsaturated sulfoxides are used, the initial formed oxysulfonium ion may undergo two different pathways the additive Pummerer reaction or the vinylogous Pummerer reaction. The following sections will consider examples from both pathways. 

For related Claisen rearrangements of sulfoxide-containing allylic vinylic ethers, see (a) T. Nakai, K. Tanaka,... 

Prilezhaeva, E. N. Rearrangements of sulfoxides and sulfones in the total synthesis of natural compounds. Russian Chemical Reviews 2001,70, 897-920. 

Russell, G. A., Mikol, G. J. Acid-catalyzed rearrangements of sulfoxides and amine oxides. The Pummerer and Polonovski reactions. Mech. 

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