Q.62. - Organic Chemistry

Question

Question: Devise a synthesis of each compound from $\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{O}}_{\mathbf{2}}\mathit{E}\mathit{t}$ , benzene, and alcohols having ≤ 2 C's. You may also use any required organic or inorganic reagents.

Step-by-Step Solution

Answer

Answer

a. Ethyl butyrate undergoes a reaction with NaOEt, followed by hydrolysis to form  $\beta$-keto esters. This is followed by a reaction with NaOEt and benzyl bromide. The final product is then obtained by the reduction of carbonyl, followed by hydrolysis of ester.

b. The product is formed from the Claisen condensation of acetophenone and ethyl butyrate.

Step 1: Claisen condensation

A characteristic reaction of an ester is the nucleophilic substitution reaction. This is because the alkoxy group is a better leaving group than the hydroxyl group.

One example of such nucleophilic reaction is the Claisen condensation, in which esters with  $\mathit{\alpha }$-hydrogens react to form  $\mathit{\beta }$-keto esters.

The reaction is driven by the deprotonation of the ester, forming an enolate.

The mechanism is similar to aldol condensation, but substitution occurs instead of addition.

Step 2: Crossed Claisen condensation

When Claisen condensation occurs between two different carbonyls, one of them necessarily being an ester, it is called crossed Claisen condensation.

A crossed Claisen condensation occurs between an ester with  $\alpha$-hydrogen and an ester without  $\alpha$-hydrogen, and only one diketone is formed. Therefore, these reactions can be used for the synthesis of beta diketones.

Esters without  $\alpha$-hydrogens can also react with ketones in Claisen condensation to form diketones. In these reactions, the enolate is formed from ketone, which reacts with ester.

Step 3: Synthesis of the given compounds

a. Ethyl butyrate undergoes reaction with NaOEt, followed by hydrolysis to form  $\beta$-keto esters.

Reaction of ester with NaOEt

This is followed by a reaction with NaOEt and benzyl bromide. The final product is then obtained by the reduction of carbonyl, followed by hydrolysis of ester.

Synthesis of a

b. The product is formed from the Claisen condensation of acetophenone and ethyl butyrate.

Acetophenone is prepared by Friedel-Crafts addition of acyl chloride to benzene. The acyl chloride is obtained from ethanol by oxidation, followed by a reaction with thionyl chloride.

Synthesis of b