The Dieckmann condensation is an organic reaction used to form a carbon-carbon bond between two tethered ester groups using an alkoxide base in alcohol to make a cyclic β-keto ester. This reaction is essentially an intramolecular form of the Claisen condensation. One ester group of the starting material must have an α-hydrogen which is abstracted by the base to form an enolate and alcohol. The enolate then attacks the carbonyl carbon of another ester molecule, an OR group is released to regenerate the base, and the final β-keto ester product is formed. The product in base is then deprotonated again to form another enolate intermediate and acid-workup is required to isolate the final cyclic β-keto ester product.
Dieckmann, W. Ber. Dtsch. Chem. Ges. 1894, 27, 102–103.