Pyrrolidine, a secondary amine, reacts with isobutyraldehyde, under the sort of conditions you would use to make an imine, to give an enamine. The name enamine combines ‘ene’ (C=C double bond) and ‘amine’.

The mechanism consists of the same steps as those that take place when imines form from primary amines, up to formation of the iminium ion. This iminium ion has no N–H proton to lose, so it loses one of the C–H protons next to the C=N to give the enamine. Enamines, like imines, are unstable to aqueous acid.

●Imines and enamines

• Imines are formed from aldehydes or ketones with primary amines.

• Enamines are formed from aldehydes or ketones with secondary amines. Both require acid catalysis and removal of water.

Enamines of primary amines, or even of ammonia, also exist, but only in equilibrium with an imine isomer. The intercom-version between imine and enamine is the nitrogen analogue of enolization, which is discussed in detail in Chapter 20.

مواضيع ذات صلة

Cyanide will attack iminium ions: the Strecker synthesis of amino acids

Lithium aluminium hydride reduces amides to amines

Iminium ions can react as electrophilic intermediates

Iminium ions and oxonium ions

Some imines are stable

Imines are usually unstable and are easily hydrolysed

Imines are the nitrogen analogues of carbonyl compounds

Amines react with carbonyl compounds

Modifying reactivity using acetals

Cyclic acetals are more stable than acyclic acetals

Acetals hydrolyse only in the presence of acid

Amines from imines: reductive amination