2.1 Principles

The reaction involves the generation of an electrophilic species with the aid of an acid which undergoes reaction with nucleophile. The electrophiles may be formed from an alkyl or acyl halide by treatment with a Lewis acid, e.g.

or, more generally, by the addition of a proton to a double bond.

or a carbonyl group, as in the self-condensation of aldehydes and ketones, e.g.

The electrophiles in the Mannich reaction are generated from an aldehydes and an amine in the presence of an acid e.g.

The nucleophiles may be an alkene, an enol or a compound of related type.