Acetate enolate synthon, chiral

The importance of the (Z)-enolate substitution has been noted elsewhere in this chapter (see Table 32). A practical solution to the generation of a useful chiral acetate enolate synthon has been to employ a substituted enolate where the ligand Rj may be removed after the aldol condensation. Enolate 149b (Rj = SMe) serves this purpose adequately (eq. [102]). The resultant alddl adducts 151b... 

This affords the L-acetal 10 via hypochlorite treatment of the intermediate 3,4-acetal of L-erythrose 9. The protected O-alkylidene glyceraldehydes are extremely flexible and can be converted into a plethora of other chiral synthons with a wide selection of uses using very standard chemical transformations (scheme 5). One major limitation for its use is the ease of racemization of the chiral center because of the ease of enolization of the aldehyde group. This is especially true even in the mildest of basic conditions. 

Solladi6 also reported a high-yielding, stereospecific synthesis of enantio-merically pure (i )-(+)a—sulfinylacetate (7), a synthetically useful chiral synthon, by nucleophilic displacement of the 0-menthyl group of (5H-)-(2) by the magnesium enolate of f-butyl acetate (Scheme 2.8) [16]. 

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