Q45E - Organic Chemistry (Mcmurry)

Question

The Mannich reaction of a ketone, an amine, and an aldehyde is one of the few three-component reactions in organic chemistry. Cyclohexanone, for example, reacts with dimethylamine and acetaldehyde to yield an amino ketone. The reaction takes place in two steps, both of which are typical carbonyl-group reactions.

 

(a) The first step is reaction between the aldehyde and the amine to yield an intermediate iminium ion $\left(R_{2}C=N{R_2}^{+}\right)$ plus water. Propose a mechanism, and show the structure of the intermediate iminium ion.

 

(b) The second step is reaction between the iminium ion intermediate and the ketone to yield the final product. Propose a mechanism.

Step-by-Step Solution

Answer

Cyclohexanone reacts with dimethylamine and acetaldehyde and produces the product.

Mechanism for first step (a)

The mechanism for the reaction is as follows,

Mechanism for second step (b)

The mechanism for the reaction is as follows,