What's the mechanism of a Claisen condensation?

The Claisen condensation is a carbon-carbon bond forming reaction that occurs between two esters or one ester and a carbonyl compound in the presence of a base.

The Claisen condensation is a fundamental reaction in organic chemistry, named after the German chemist Rainer Ludwig Claisen. It involves the condensation of two esters or an ester and a carbonyl compound to produce a β-keto ester or a β-diketone. This reaction is base-catalysed, typically using a strong base like sodium ethoxide.

The mechanism of the Claisen condensation involves several steps. Firstly, the base deprotonates the alpha hydrogen of the ester, forming an enolate ion. This enolate ion is a strong nucleophile and attacks the carbonyl carbon of the second ester, forming a tetrahedral intermediate. This intermediate then collapses, expelling the alkoxide ion and forming a new carbon-carbon bond. The alkoxide ion then deprotonates the newly formed β-keto ester, forming the final product and regenerating the base.

The Claisen condensation is a powerful tool in organic synthesis, allowing for the formation of complex molecules from simpler precursors. It is particularly useful in the synthesis of β-keto esters, which can be further manipulated to produce a wide range of other compounds. The reaction is highly stereospecific, meaning that it produces a single, predictable product.

The Claisen condensation is an example of a condensation reaction, where two molecules combine with the loss of a small molecule, in this case an alcohol. It is also an example of a nucleophilic acyl substitution, where a nucleophile attacks a carbonyl carbon, leading to the substitution of the carbonyl group. This reaction is a key part of many synthetic routes in organic chemistry, and understanding its mechanism is crucial for any student of the subject.