Aldol Reactions of Other Carbonyl Compounds

The enolates of other carbonyl compounds can be used in mixed aldol condensations. Extensive use has been made of the enolates of esters, thioesters, and amides. Of particular importance are several modified amides, such as those derived from oxazolidinones, that can be used as chiral auxiliaries. The methods for formation of these enolates are similar to those for ketones. Lithium, boron, tin, and titanium derivatives have all been used. Because of their usefulness in aldol additions and other synthetic methods (see especially Section 6.4.2.3, Part B), there has been a good deal of interest in the factors that control the stereoselectivity of enolate formation from esters. For simple esters such as ethyl propanoate, the E-enolate is preferred under kinetic conditions using a strong base such as EDA in THE solution. Inclusion of a 

These observations are explained in terms of a cyclic TS for the LDA/THF conditions and a more open TS in the presence of an aprotic dipolar solvent. 

Addition of Enolates and Enols to Carbonyl Compounds TheAldol Addition and Condensation Reactions 

Addition, Condensation and Substitution Reactions of Carbonyl Compounds 

Phenyl and phenylthio esters have proven to be advantageous in TiCl4-mediated additions, perhaps because they are slightly more acidic than the alkyl analogs. The reactions show syn diastereoselectivity.  

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