Convenient primary amidation of N-protected phenylglycine and dipeptides without racemization or epimerization

Primary amidation of N-protected phenylglycine and dipeptide proceeded easily to afford the corresponding amides in 57–95% yields with 99% ee and 81–99% de, respectively. The procedure is very easy to avoid racemization and epimerization of the products in the reactions by keeping exactly the reaction temperature at −15 °C when the activation of carboxylic acids, followed by the reaction of the mixed carbonic carboxylic anhydride with NH₄Cl.