Diastereoselective alkylation of chiral enolates

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. 

There are numerous examples of diastereoselective alkylations of chiral enolates, in which the extant asymmetry of the substrate exerts suitable stereochemical control in the alkylation step [15, 20]. Several useful guiding principles have been determined to aid in predicting the stereochemical outcome. The examples discussed in the following sections have been selected to showcase the power of enolate alkylations for the stereoselective formation of new C-C bonds, as well as to highlight selected historical aspects in the development of the field. 

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