The Claisen condensation involves the reaction of esters in basic medium forming 3-ketoesters
Mechanism:
Step 1. Formation of the ester enolate
Step 2. Nucleophilic addition
Stage 3. Ethoxide removal
The displacement of the equilibria is produced by the subtraction of the acid hydrogen in the final keto ester, forming an enolate that is protonated in the second stage.
