We investigated the reaction of 7-methoxy-4-chloromethylcoumarin and ethyl (diethoxyphosphoryl) acetate in various solvents in the presence of various bases, which led us to the synthesis of ethyl 2-(diethoxyphosphoryl)-3-(7-methoxy-2-oxo-2H-chromen-4-yl) propanoate. It was found that the ratio of 4-chloromethylcoumarin / ethyl (diethoxyphosphoryl) acetate / sodium hydride 1: 2: 2 using dimethylformamide as the solvent was optimal. Alkaline hydrolysis of ester with lithium hydroxide excess affords new 2-(ethoxyphosphoryl)-3-(7-methoxy-2-oxo-2H-chromen-4-yl) propionic acid
