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.


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.


Step 3. Hydrolysis of the iminium salt

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


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