The reactivity of acylimidazoles

Amides are already acylated amines, and have a low reactivity in nucleophilic reactions because the amide carbonyl group is more negatively charged than the carbonyl groups of normal esters (4) and of ketones, because of the delocalization of the lone pair of electrons on the nitrogen into the carbonyl group (equation (5)). 

Acylation involves the introduction of an acyl group into a molecule with a replaceable hydrogen atom (see also Table 1). 

Less commonly, an acyl group may be added across a double bond. 

The acylating agent R—C( 0)-X can lose the group -X by (a) electrophilic, (b) nucleophilic or (c) free radical mechanisms, represented in equation (3). 

Direct electrophilic acylations of the first of these tyf es are the most common mode of acylation (I). The mechanism of acylation, particularly of alcoholic groups, is of course essentially the same as that for esterification, so for further consideration the relevant section of Chapter 

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