Intramolecular Claisen condensation
Dieckmann condensation
How the Dieckmann condensation works, in 3 steps. Each step shows the structures and the curved arrows that move the electrons.
In short. A 3-step mechanism. Typical reagents: NaOEt (≥1 equiv), diethyl adipate. Conditions: EtOH or toluene, reflux; then H₃O⁺ workup. Bonds formed: Ring C–C bond (Cα–C=O); bonds broken: α C–H; C–OEt. Stereochemistry: New stereocentre — racemic. Rate and selectivity: 5- and 6-membered rings best; driven by β-keto ester deprotonation.
At a glance
Step 1: Enolate formation
An alkoxide base deprotonates the α-carbon of one ester group in a diester, forming an ester enolate. The base should match the ester's alkoxy group (ethoxide with ethyl esters) so that any attack on the ester carbonyl is invisible.
Step 2: Intramolecular attack closes the ring
The enolate attacks the other ester carbonyl in the same molecule, closing a ring. Five- and six-membered rings form best (from 1,6- and 1,7-diesters), and the tetrahedral intermediate then expels alkoxide.
Step 3: Collapse, deprotonation, workup
The product is a cyclic β-keto ester. The reaction is driven by deprotonating that product between its two carbonyls (pKa about 11) — the same thermodynamic sink as the ordinary Claisen condensation — so a full equivalent of base is needed, and acid workup then gives the neutral β-keto ester.
Abbreviations and terms
- OEt
- Ethoxy. –OCH₂CH₃.
- EtOH
- Ethanol. Polar protic solvent.
- NaOEt
- Sodium ethoxide. Alkoxide base matched to ethyl esters (avoids transesterification).
- pKa
- Acid-dissociation constant (–log). Lower pKa = stronger acid; used to judge which proton a base removes.
How it compares with related reactions
| Dieckmann condensation | Claisen condensation of ethyl acetate | Claisen-Schmidt condensation | |
|---|---|---|---|
| Reagents | NaOEt (≥1 equiv), diethyl adipate | Ethyl acetate (2 equiv), NaOEt (≥ 1 equiv); then H₃O⁺ | Methyl ketone (ArCOCH₃), ArCHO (no α-H), NaOH or KOH |
| Conditions | EtOH or toluene, reflux; then H₃O⁺ workup | EtOH, reflux; same alkoxide as ester OR group | EtOH/H₂O, 0–25 °C |
| Stereochemistry | New stereocentre — racemic | None (achiral product) | E-chalcone (thermodynamic) |
| Rate / selectivity | 5- and 6-membered rings best; driven by β-keto ester deprotonation | Equilibrium pulled forward by deprotonating the β-keto ester (pKa ≈ 11) | Aldol addition reversible; E1cB dehydration drives it forward |
Test yourself
Try to answer each question before opening it.
Which reagents and conditions are typical for the Dieckmann condensation?
NaOEt (≥1 equiv), diethyl adipate. Conditions: EtOH or toluene, reflux; then H₃O⁺ workup.
Which bonds are formed and which are broken?
Formed: Ring C–C bond (Cα–C=O). Broken: α C–H; C–OEt.
What is the stereochemical outcome?
New stereocentre — racemic
What controls the rate or the selectivity?
5- and 6-membered rings best; driven by β-keto ester deprotonation
Study guides that help with this reaction
- Carbonyl chemistry: addition, acyl substitution and enolates
- SN1, SN2, E1 or E2? How to decide which mechanism wins
- Nucleophiles, electrophiles and leaving groups: what makes a reaction go