Ammonium ylides, cyclic 2.3- sigmatropic rearrangements

Sigmatropic rearrangements of cyclic sulfonium and ammonium ylides have been extensively used in ring contraction and ring enlargement methods. An example is shown in Scheme 55. 

Sulfur and ammonium ylides are susceptible to [2,3]-sigmatropic rearrangements under mild conditions with efficient transfer of chirality, as Trust and Ham-men showed in 1973 [1626], Most of the applications of these rearrangements have been conducted on chiral synthons [1622]. Kurth and coworkers [1627, 1628] have applied this reaction to the synthesis of P-chiral, y,8-unsaturated acids via the rearrangements of cyclic sulfonium ylides 10.21, starting from thiol 10.22 (Figure 10.9). 

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