Theory and Defination :

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.

General Reaction :


<img src="curtius-rearrangement.jpg" alt="cyclic β-keto ester synthesis by curtius earrangement mechanism "/>


Mechanism :


The mechanism is similar to the Claisen Condensation.Adipic acid is treated with sodium ethoxide so that carbanion is formed.The carbanion attacks the carbonyl group of the same molecule (intramolecular condensation) forming cyclic product.Ethanol is removed once it is protonated and hence the product (2-Oxocyclopentene Carboxylate) is formed.

<img src="curtius-rearrangement.jpg" alt="cyclic β-keto ester synthesis by curtius earrangement mechanism "/>



















Examples and Application :


1.Synthesis of Tetronic Acids from Esters


<img src="curtius-rearrangement.jpg" alt="cyclic β-keto ester synthesis by curtius earrangement mechanism "/>

2. Synthesis of 4,4-Disubstituted Cyclohexane β-Keto Esters

<img src="curtius-rearrangement.jpg" alt="cyclic β-keto ester synthesis by curtius earrangement mechanism "/>