Ester Enolates and the Claisen Condensation | Organic Chemistry 3
Ester enolates and Claisen condensation are studied in this chapter: acidity and formation of β-dicarbonyl compounds, nucleophilicity of β-dicarbonyl anions, 3-ketoacids decarboxylation, malonic ester synthesis, Michael addition
Acidity of the β-Dicarbonyls
The acidity of β-dicarbonyl is due to the resonance stabilization of the corresponding anion
Formation of β-Dicarbonyl compounds
Claisen Condensation:
Mechanism:
- Ester enolate formation:
- Nucleophilic addition:
- Elimination followed by deprotonation:
- Protonation upon acidic aqueous work-up:
The Claisen condensation is an equilibrium: a retro-Claisen condensation can be observed resulting in 2 ester molecules via a mechanism which is exactly the reverse of the forward reaction
Other Methods to form β-Dicarbonyl Compounds
Dieckmann Condensation: Intramolecular Claisen Condensation
Mixed Claisen reaction: Ester + Ketone
Nucleophilicity of β-Dicarbonyl Anions
Mechanism:
- Enolate formation by deprotonation
- Enolate alkylation via a SN2
3-Ketoacids Decarboxylation
Mechanism:
- Hydrolysis:
- Decarboxylation:
Malonic Ester Synthesis
Mechanism:
- Enolate formation
- Enolate alkylation
- Hydrolysis
- Decarboxylation
Michael Addition
Mechanism: 1,4-addition