Chiral auxiliary also oxathiane

A 1,3-oxathiane chiral auxiliary derived from camphor has also been reported [58]. 

Chiral induction can also be quite effective when the locus of asymmetry is attached to the sulfur ylide itself The sulfonium salt 637, derived from Eliel s oxathiane, can be used to deliver a benzylic center to tosylimines (e.g., 638) and efficiently produces phenylaziridines with a very high degree of asymmetric induction. The method is amenable to gram-quantity synthesis, and the chiral auxiliary can be easily recovered. In general, cisitrans-mxxtmcs are obtained, depending upon the steric bulk of the imine substituent (Scheme 156) <2004JOC1409>. 

The reduction of 2-acyl- 1,3-oxathianes such as 3.96 (X = S) or of 2-acyl-3-oxa-N-benzylpiperidines 3.96 (X = NCH2Ph) can also take place with or without chelation control [El, EFl, EH2, KEl, KF4]. In cases of chelation control, the oxygen atom of the heterocycle participates in the chelation process (Figure 3.32). When the reaction is carried out with Li(5-Bu)3BH in the presence of Lil as an additive, the reduction occurs under chelation control. However, when using two equivalents of DIBAH, each of them coordinates to a one basic site, and no chelation takes place. The use of these chiral auxiliaries allows the synthesis of nonracemic a-hydroxyaldehydes or a-hydroxyesters with a high enantiomeric excess [NNl, S3]. 

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