Dieckmann condensation: practice and mechanism
The Dieckmann condensation is an intramolecular Claisen condensation. A 1,6-diester gives a five-membered ring, a 1,7-diester a six-membered ring, each a cyclic β-keto ester.
Example
The intramolecular Claisen condensation: the enolate at one end of the diester attacks the ester group at the other end. 1,6-Diesters give five-membered rings, 1,7-diesters six-membered rings, each as a cyclic β-keto ester.
Mechanism step by step
- 1
Ethoxide deprotonates the α-carbon next to one of the two ester groups.
- 2
The enolate attacks the other ester group in the same molecule; ethoxide leaves and the ring closes.
- 3
The cyclic β-keto ester is deprotonated (driving force) and acidic workup gives the product.
Practice tasks
Which product forms, which reagent is needed? After each answer you see the explanation.
Which main product forms?
Typical mistakes
- NaOEt in ethanol does not hydrolyse the ester: ethoxide on an ethyl ester only swaps EtO for EtO. The base forms the enolate for ring closure.
- One of the ester groups is kept. The product is a β-keto ester; the cyclic ketone without the ester only forms after hydrolysis and decarboxylation.
- NaOEt is not a reducing agent. The ester groups do not become alcohols; that would be LiAlH₄.
Often confused with: Claisen condensation · Ester hydrolysis (saponification)
Frequently asked questions
Which ring sizes form?
Five- and six-membered rings: diethyl adipate (1,6) gives a cyclopentanone ester, diethyl pimelate (1,7) a cyclohexanone ester.
How do I get the plain cyclic ketone?
Hydrolyse the β-keto ester and heat: the β-keto acid decarboxylates, leaving cyclopentanone or cyclohexanone.