The Mannich reaction allows the reaction of an enol with formaldehyde ( CHO ) through the use of a secondary amine (usually cyclic secondary amines are used, but theoretically it could also be used primary amine). The importance of the Mannich reaction is the possibility to form a new single C-C bond.
Since formaldehyde is a very reactive substrate, with it we can not perform, for example, an aldol condensation. This makes the reaction even more interesting.
Mechanism
The amine that results from this reaction is called " Mannich base ". To even better explain the dell'enolo reaction of the iminium salt, consider that we can describe two forms of resonance; the one on the right justifies the electrophilicity of the carbon on which the nucleophile attack takes place.
Obtaining the corresponding ketone (or aldehyde)
Although from the point of view of organic synthesis can be very useful to obtain an amino-ketone (or aldehyde), it is very likely that you will want to add to our initial product only a new carbon - carbon bond. How can we eliminate the amine portion of the molecule? It's very easy. We'll make our compound acting in a SN2 on iodo - methane and the treating with base.
Actually, today we opt for other routes because of extreme toxicity of iodo - methane
In summary ...
Let's have a look to some examples of Mannich reaction:
