(1) Diketene is treated with chlorine in methylene chloride, ethyl chloroacetoacetate is extracted, and the compound is reacted with methylene chloride at room temperature for 10 hours to obtain 2,4-dichloroacetoacetic acid ethyl ester. Ethyl 2-chloromethyl-ethylnicotinate was prepared by refluxing with 2-ethylacrolein and ammonium sulfamate in anhydrous ethanol for 1.5 hours to prepare 2-amino-2,3-dimethyl Butanamide and sodium bicarbonate were reacted in dimethyl sulfoxide at 80° C. for 6 h. The resulting condensation product was hydrolyzed and then cyclized in acetic acid to obtain imazethapyr.
(2) 2,3-pyridinedicarboxylic acid is reacted with acetic anhydride in toluene to form dipicolinic anhydride, and then reacted with (CH3)2CHCOH3(CN)NH2 at 10-12°C to form carbamoyl nicotinic acid, Hydrogen peroxide was hydrolyzed in an aqueous sodium hydroxide solution, and finally heated to 70° C. to cyclize to obtain imazapyr.