preparation | . The method is to first add 4-(acetylamino) -2-hydroxy-3-(2-hydroxyethyl) benzoate methyl ester to an organic solvent, add triphenylphosphine and diethyl azodicarboxylate to close the ring to obtain 4-acetylamino -2, 3-dihydrobenzofuran-7-methyl acetate crude product, the crude product 4-acetamido-5-chloro-7-benzofuran-formate was directly chlorinated with N-chlorinated succinimide to obtain the crude product 4-acetamido-5-chloro-2-dihydrobenzofuran-7-carboxylic acid by hydrolysis and purification to obtain the pure product 4-amino-5-chloro-2, 3-dihydrobenzofuran-7-carboxylic acid. |