Mild and efficient synthesis of carboxylic acid anhydrides from carboxylic acids and triazine coupling reagents

Anhydrides of carboxylic acids were obtained in 53%-95% yield by treatment of appropriate carboxylic acids with 2-chloro-4,6-dimethoxy1,3,5-triazine (CDMT) or 2,4-dichloro-6-methoxy-1,3,5-triazine (DCMT) in the presence of N-methylmorpholine. It has been proved that synthesis proceeds via triazine active esters 3a,b, which are able to acylate carboxylate anion but not less nucleophilic carboxylic acid.