Acylation of enolate anions the Claisen reaction

Nucleophilic addition of an enolate anion from a carboxylic acid derivative onto an aldehyde or ketone is simply an aldol-type reaction (see Section 10.3). 

A simple example is shown again, LDA is used to generate the enolate anion, and addition to the ketone is carried out as a second step (see Section 10.2). 

In the aldol reaction, we saw an enolate anion acting as a nucleophile leading to an addition reaction with aldehydes and ketones. 

Now this is exactly the same situation we encountered when we compared the reactivity of aldehydes and ketones with that of carboxylic acid derivatives (see Section 7.8). The net result here is acylation of the nucleophile, and in the case of acylation of enolate anions, the reaction is termed a Claisen reaction. It is important not to consider aldol and Claisen reactions separately, but to appreciate that the initial addition is the same, and differences in products merely result from the absence or presence 

The Claisen reaction (sometimes Claisen condensation) is formally the base-catalysed reaction between two molecules of ester to give a P-ketoester. Thus, from two molecules of ethyl acetate the product is ethyl acetoacetate. 

---