A novel method of complete activation by carbonyldiimidazole: application to ester synthesis

The activation of carboxylic groups by carbonyldiimidazole (CDI) results in the presence of excess CDI; it is shown that this reacts rapidly with the target hydroxyl groups under acylation conditions, thus preventing the desired acylation even when an excess of reagent is present and resulting in poor yields. The methods described result in rapid, complete, and convenient removal of the excess CDI. This procedure thus permits the use of sufficient excess of CDI to effect complete activation of the acid to the imidazolide. The imidazolides prepared in this manner, when used in limiting amounts, can be quantitatively converted to esters or amides; when used in slight excess, these imidazolides result in the quantitative acylation of target groups.