Enolates a-hydroxylation

Many metal enolate a-hydroxylations have been performed with racemic fra r-2-phenylsulfonyl-3-phenyloxazir-idine 33 because it is more reactive than the enantiomerically pure camphor-derived A -sulfonyloxaziridines (Equation 11). Examples are given in Table 20. 

The first three sections of this chapter describe diastereoselective alkylations of chiral enolates including heteroatom-substituted enolates [15, 20]. Section 3.4 deals with the class of enolate alkylations that have typically been included under the rubric of chiral-auxiliary-controlled processes. As suggested by the term, the auxiliary is only transiently utilized and, following alkylation, is subsequently excised. The facile use of chiral auxiliaries in asymmetric enolate alkylations has played and continues to play a pivotal role in the stereoselective formation of new C-C bonds. After a brief survey of the relatively few developments in catalytic enantioselective enolate alkylations (Section 3.5) [21, 22], selected examples of enolate a-hydroxylations (Section 3.6) [23-25] and a-halogenations (Section 3.7) [26, 27] are covered. The corresponding a-aminations of enolates are discussed in Chapter 10, describing stereoselective formation of a-amino acids. 

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