The Claisen ester condensation and other self-condensations
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص642-643
2025-06-29
612
The self-condensation of ethyl acetate is the most famous example of the Claisen ester condensation and it works in good yield under convenient conditions. The product (ethyl aceto acetate) is commercially available for this very reason—and cheap too—so you are unlikely to want to do this particular example. A more generally useful reaction is the self-condensation of simple substituted acetates RCH2CO2Et. These work well under the same conditions (EtO− in EtOH). The enolate anion is formed first in low concentration and in equilibrium with the ester. It then carries out a nucleophilic attack on the more abundant unenolized ester molecules.
These steps are all unfavourable equilibria and, on their own, would give very little product. However, as we mentioned before, the reaction works because the equilibrium is driven over by the essentially irreversible formation of a stable, delocalized enolate from the product.
Finally, the reaction is worked up in acid and the β keto-ester product is formed. Notice that all products of Claisen ester condensations have a 1,3-dicarbonyl relationship. These com pounds are useful in the preparation of specific enol equivalents and you have seen them in action.
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