Ketones, ethyl titanium enolate, chiral auxiliary

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... 

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