Examples of Claisen Condensation

The Claisen condensation is a carbon–carbon bond-forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-keto ester or a β-diketone. Here are some examples of the Claisen condensation:

• Synthesis of natural products: Claisen condensation is used to synthesize various natural products, such as the formation of the A ring of the antibiotic erythromycin.
• Synthesis of pharmaceuticals: The Claisen condensation is employed in synthesizing various pharmaceuticals, such as the anticonvulsant drug phenytoin.
• Biosynthesis of fats and terpenes: Acetyl CoA, a key molecule in metabolism, undergoes a Claisen condensation, leading to the formation of complex lipids and terpenes.

Reverse Claisen Condensation

The reverse Claisen condensation is the reverse of the Claisen condensation reaction, where a β-keto ester or a β-diketone is converted back into two esters or an ester and another carbonyl compound in the presence of a strong acid or a Lewis acid. The reaction proceeds through the protonation of the carbonyl oxygen of the β-keto ester or β-diketone, followed by the cleavage of the carbon-carbon bond and the formation of two esters or an ester and another carbonyl compound.

The reverse Claisen condensation is generally less favorable than the forward reaction due to the thermodynamic stability of the β-keto ester or β-diketone product. The reaction can be helpful in synthesizing esters or carbonyl compounds from β-keto esters or β-diketones. The general reaction for the reverse Claisen condensation is:

keto ester or diketone + acid → two esters or ester and carbonyl compound

Intramolecular Claisen Condensation

The intramolecular Claisen condensation, also known as the Dieckmann condensation, is a variation of the Claisen condensation where a molecule containing two ester groups undergoes a cyclization reaction to form a cyclic β-keto ester. The reaction proceeds by forming an enolate ion from one of the ester groups, which then attacks the carbonyl carbon of the other ester group to form a cyclic intermediate.

The intermediate then undergoes protonation and dehydration to form the final product. The Dieckmann condensation is particularly useful for synthesizing five- and six-membered cyclic β-keto esters. The general reaction for the intramolecular Claisen condensation is:

keto ester with two ester groups → cyclic keto ester

Claisen condensation is an organic reaction that forms a new carbon-carbon bond, producing a β-keto ester. It involves the condensation of two esters or one ester and a carbonyl compound in the presence of a strong base, forming a β-keto ester or a β-diketone. It was discovered by German chemist Ludwig Claisen in 1887. In this article, we will look into What Claisen Condensation is, its mechanism, examples, types, etc.