Firstly, adding methyl 4-(acetyl amino)-2-hydroxy-3-(2-hydroxy ethyl) benzoate into an organic solvent, adding triphenylphosphine and azo dioctyl phthalate diethyl ester, performing cyclization to obtain a methyl 4-acetamido-2,3-dihydro benzofuran-7-formate rough product, directly chloridizing the rough product by using N-chloro succinimide to obtain a rough product methyl 4-acetamide amino-5-chloro-7-benzofuran formate, and performing hydrolysis and purification to obtain a 4-amino-5-chloro-2,3-dihydrobenzofuran-7-carboxylic acid pure product.
