Q72E - Organic Chemistry (Mcmurry)

Question

The third and fourth steps in the synthesis of Hagemann’s ester from ethyl acetoacetate and formaldehyde (Problem 23-71) are an intramolecular aldol cyclization to yield a substituted cyclohexenone, and a decarboxylation reaction. Write both reactions, and show the products of each step.

Step-by-Step Solution

Answer

In the third step, the enolate ion formed in second step (previous problem) attacks the carbonyl carbon and forms a cyclic alkoxide ion. Then Protonation of the alkoxide and dehydration on heating forms the cyclohexenone. In the fourth step, the cyclohexenone is hydrolysed by dilute acid and then decarboxylation on heating forms the Hagemann’s ester.

Reaction of the third step

The third step for preparation of Hagemann’s ester is an intramolecular aldol cyclization which yields a substituted cyclohexenone.

Product of the third step

The substituted cyclohexenone product is

Reaction of the fourth step

The decarboxylation reaction is

Product of the second step

The product of this step is

Explanation of the solution

For the third step:

 

The enolate ion formed in second step (previous problem) attacks the carbonyl carbon and forms a cyclic alkoxide ion. Then Protonation of the alkoxide and dehydration on heating forms the cyclohexenone.

 

 

For the fourth step:

 

The cyclohexenone is hydrolysed by dilute acid and then decarboxylation on heating forms the Hagemann’s ester.