A facile and green synthetic process of pyriminobac-methyl

Pyriminobac-methyl is an important herbicide widely used for weed control in direct-seeding rice fields. The traditional synthetic methods usually involve n-butyl lithium or diazotization reaction, resulting in serious safety issues or environmental problems. In this work, 3-chlorophthalic anhydride was used as a raw material to synthesize pyriminobac-methyl. 3-chlorophthalic anhydride was first reacted with potassium hydroxide in the presence of cuprous chloride and then reacted with acetic anhydride to give 3-hydroxyphthalic anhydride with a total yield of 66%. 3-hydroxyphthalic anhydride was then reacted with diethyl malonate (yield 60%) and subsequently hydrolyzed to obtain 2-acetyl-6-hydroxybenzoic acid with a yield of 80%. After esterification with methanol (yield 90%) and imidization with methoxamine hydrochloride (yield 88%), 2-hydroxy-6-(1-methoxyiminoethyl)benzoic acid methyl ester was obtained. Finally, 2-hydroxy-6-(1-methoxyiminoethyl) benzoic acid methyl ester was reacted with 2-methylsulfonyl-4,6-dimethoxypyrimidine in the presence of potassium carbonate to obtain pyriminobac-methyl with a yield of 87%. Compared to the traditional synthetic processes of pyriminobac-methyl, our new synthetic process is safer, more facile, and environmental-friendly.