15.30: Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization
Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic β-ketoester as the final product. Commonly, 1, 6 and 1, 7-diesters are preferred substrates for the reaction since the generated five, and six-membered cyclic β-keto esters are particularly more stable.
In the reaction, α carbon connected to one end of the ester ends serves as an enolate nucleophile after losing its proton to the base. The carbonyl carbon of the ester group at the other end of the same molecule functions as the electrophilic site. The enolate, through an intramolecular nucleophilic attack on the carbonyl carbon, cyclizes the molecule to form a stable ring intermediate. The intermediate reacts with the base and generates another enolate ion, which is neutralized to form the final β-ketoester. The second deprotonation step is the driving force for the reaction to go to completion.
The formed product can undergo alkylation and decarboxylation to produce substituted cyclic ketones.