Ester Enolates and the Claisen Condensation | Organic Chemistry 3

The Ester Enolates and the Claisen Condensation are studied in this chapter: the acidity and formation of β-dicarbonyl compounds, the nucleophilicity of β-dicarbonyl anions, the 3-ketoacids decarboxylation, the malonic ester synthesis, the 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:
 

Step 1: Ester Enolate Formation


Step 2: Nucleophilic Addition


Step 3: Elimination followed by a Deprotonation


Step 4: Protonation upon acidic aqueous work-up

 

Claisen condensation is an equilibrium: a retro-Claisen condensation can be observed, giving two molecules of simple ester through a mechanism that is the exact 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:

Step 1: Enolate formation by deprotonation
Step 2: Enolate alkylation via a SN2

3-Ketoacids Decarboxylation

 

Mechanism:
 

Step 1: Hydrolysis


 

Step 2: Decarboxylation

Malonic Ester Synthesis

 

Mechanism:

Step 1: Enolate formation
Step 2: Enolate alkylation
Step 3: Hydrolysis
Step 4: Decarboxylation

Michael Addition

 

Mechanism: 1,4-Addition