Reaction of enolates with iminium ions or imines

4 Reaction of enolates with iminium ions or imines Mannich reaction 

Instead of alkyl halides other electrophiles, such as imines or iminium ions, are also used for the nucleophilic attack of enolates. Primary amines react with aldehydes and ketones to produce imines °. For example, the reaction of acetophenone with methyl amine gives 

However, the reaction of secondary amine such as dimethyl amine with formaldehyde and acetone gives the corresponding Mannich base, 3.31. 

Although formaldehyde has been most common, other aldehydes have also been used successfully for the formation of iminium ion. The Mannich reaction also proceeds with the other activated hydrogen compounds such as indole, furan, pyrrole and phenols. When primary amine is used, the Mannich base formed is a secondary amine and may undergo further condensation to yield tertiary amine. The Mannich base may eliminate an amine 

Two main strategies for the catalytic asymmetric alkylation of imines are (a) chiral Lewis acid approach and (b) chiral nucleophilic approach. 

---