Chiral auxiliary sigmatropic rearrangements

It has been found that the thermodynamic ratio of isomeric allylic azides, interchangeable by stereoselective [3,3]-sigmatropic rearrangement, can be affected by steric and electronic factors in the presence of a bulky (chiral) auxiliary. Under Mit-sunobu conditions, treatment of allylic alcohols (48 R Ph) was shown to give a... 

The next example makes more involved use of these [2,3]-sigmatropic allylic sulfoxide-allylic alcohol rearrangements. It comes from the work of Evans (he of the chiral auxiliary) who, in the early 1970s, first demonstrated the synthetic utility of allylic sulfoxides. Here he is using this chemistry to make precursors of the prostaglandins, a family of compounds that modulate hormone activity within the body. 

The sulfur ylides 254 used in the stereoselective [2,3]-sigmatropic rearrangement are generated by copper(I)-catalyzed Doyle-Kirmse reaction of aryl sulfides 253 and diazo compounds bearing Oppolzer s camphor sultam auxiliary 252 in the presence of chiral diamine ligand S, S)-259 <05JA15016>. These intermediate ylides undergo spontaneous... 

In most cases, the sulfoxides produced after the asymmetric transformation are reduced with sodium or aluminium amalgam, or Raney nickel. The sulfoxide may also be reduced by LiAffl into a sulfide, winch after quaternarization becomes a leaving group [474], If the carbon skeleton of the substrate bears appropriate substituents, the sulfoxide can suffer [2,3] sigmatropic rearrangements [497, 498] or Pummerer rearrangements. In all these types of applications, the chiral auxiliary is never recovered. 

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