Novel preparation method of azasetron hydrochloride

The invention provides a novel preparation method of azasetron hydrochloride, belonging to the technical field of medicine synthesis. According to the method, methyl 5-chlorosalicylate is used as a raw material; after acetic anhydride nitrification and stannous chloride reduction at room temperature, dimethyl carbonate is used as a methylation reagent, and an intermediate V (6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-carboxylic acid methyl ester) is synthesized by adopting a one-pot method; the intermediate V is hydrolyzed to obtain 6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-8-formic acid (VI); and the compound reacts with free 3-aminoquinuclidine dihydrochloride for 1 h under the catalysis of TBTU to form a salt so as to obtain I (azasetron hydrochloride). According to the method, the yield of each step is high; aftertreatment is simple; the reaction time of each step is short; conditions are mild; low-toxicity environment-friendly reagents are adopted; energy consumption is reduced