Question

Describe how the following compounds could be prepared from cyclohexanone using an enamine intermediate:

a.

b.

Short answer

a.

b.

Step-by-step solution

Step-by-Step SolutionStep 1: Alkylating of an α-carbon via an enamine 

The enamine is prepared when a ketone reacts with a secondary amine. The alkylation of an $\mathrm{\alpha }$-carbon is done by first forming an enamine of the carbonyl compound and then reacting with alkyl halide by using the ${\mathbf{S}}_N\mathbf{2}$mechanism. After hydrolysis of imine, the $\mathrm{\alpha }$-alkylated ketone is formed.

Compound (a) preparation from cyclohexanone using an enamine intermediate

(a) The starting compound is cyclohexanone (carbonyl compound), and it is converted to an enamine by the treatment of secondary amine with a small trace of acid. By${\text{S}}_{\text{N}}\text{2}$ reaction, this enamine is reacted with${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}\text{Br}$ (alkyl halide). The imine is formed and hydrolyzed to an -alkylated ketone under acidic conditions. The protonated secondary amine is also formed along with ketone. The reaction is shown below.

Preparation of compound (a)

Compound (b) preparation from cyclohexanone using an enamine intermediate

(b) The cyclohexanone (carbonyl compound) is taken as the starting material, and it is converted to an enamine by treating secondary amine with a trace of acid. By ${\text{S}}_{\text{N}}\text{2}$reaction, this enamine is reacted with ${\text{CH}}_2{\text{=CHCOCH}}_3$(alkyl halide). The imine is formed, which is hydrolyzed under acidic conditions to an $\mathrm{\alpha }$-alkylated ketone, and along with this, the protonated secondary amine is also formed. The reaction is shown below.

Preparation of compound (b)