This invention is due to the carboxymethyl conversion reaction which happens under existing of the suitable alkylating agent and the base without necessary to watch the said reaction environment of pH, it refers the manufacturing method of the chemical compound formula (i). The chemical compound formula (i) is the useful intermediate field at the time of manufacturing the contrast medium for diagnosis of MRI technology.本発明は、pHの該反応環境を監視する必要なく、適当なアルキル化剤および塩基の存在下で起こるカルボキシメチル化反応による、式(I)の化合物の調製方法に言及する。式(I)の化合物は、MRI技術の診断用造影剤の調製において有用な中間体である。