Claisen condensation

There are a number of different combinations of enolizable and nonenolizable carbonyl compounds that form a few different types of Claisen.

In mixed Claisen condensations, a non-nucleophilic base such as lithium diisopropylamide, or LDA, may be used, since only one compound is enolizable.

LDA is not commonly used in the classic Claisen or Dieckmann condensations due to enolization of the electrophilic ester.

In the first step of the mechanism, an α-proton is removed by a strong base, resulting in the formation of an enolate anion, which is made relatively stable by the delocalization of electrons.

That is, Claisen condensation does not work with substrates having only one α-hydrogen because of the driving force effect of deprotonation of the β-keto ester in the last step.