What is the major product of the Stork enamine synthesis, that is, the reaction of cyclopentanone with pyrrolidine, heat, CH_3CH_2Br, H^+, and H_2O?

1 Answer
Apr 22, 2017

The major product is 2-ethylcyclopentanone.

Explanation:

The reaction is often called the Stork enamine synthesis.

Step 1. Formation of an enamine.

Enamine formation

Step 2. "S"_text(N)2 alkylation

The double-bonded carbon in the enamine has a partial negative charge, so it can act as a nucleophile and displace the "Br" from ethyl bromide and form an iminium salt.

Alkylation

Step 3. Hydrolysis of the iminium salt

The iminium salt is hydrolyzed to regenerate the ketone and the amine.

Hydrolysis

Note: The reaction is done this way because direct alkylation of the cyclopentanone enolate gives multiple alkylation, but the enamine stops at one alkylation.