Question

Draw the most stable form of the major mixed Claisen product formed in the following reaction.

Answer 1

Concepts and reason

The mixed Claisen condensation of two esters is given and the major product needs to be given. The Claisen condensation takes place in the presence of a base such as sodium ethoxide and results in the formation of $\beta$ ketoester.

Fundamentals

The Claisen condensation is a reaction between two esters having $\alpha$ hydrogen in presence of a base. The final product is a $\beta$ ketoester.

The base abstracts $\alpha$ hydrogen from one of the ester to form a carbanion. The carbanion then attacks the other ester molecule and forms an intermediate. Finally, an ethoxide ion is eliminated from the ester molecule to give $\beta$ ketoester.

The carbanion formed is as follows:

The carbanion attacks on the carbonyl carbon of ethyl isobutyrate.

The final product formed is as follows:

Ans:

The major product of the given reaction is as follows:

Answer 2

The second ester forms preferentially the enolate (the first step of the condensation

reaction). The ether part will be eliminated from the other ester.