Preparation of activated esters of N-alkoxycarbonylamino and other acids by a modification of the mixed anhydride procedure

Generation of a mixed anhydride using ethyl or isopropyl chloroformate and N-methylmorpholine in dichloromethane at room temperature, followed by addition of excess ring-substituted phenol or N-substituted hydroxylamine and a catalytic amount of tertiary amine, provides an efficient synthesis of activated esters.