Method for preparing 5-cyclopropyl-4-[2-methylthio-4-(trifluoromethyl)benzoyl] isoxazole

The invention relates to a method for preparing a herbicide isoxaflutole intermediate, namely, 5-cyclopropyl-4-[2-methylthio-4-(trifluoromethyl)benzoyl] isoxazole. The method comprises the following steps: condensing 3-cyclopropyl-1-(2-methylthio-4-trifluoromethylphenyl)propyl-1,3-dione and triethyl orthoformate as starting materials to prepare 1-(4-trifluoromethyl-2-methylthio-phenyl)-3-cyclopropyl-2-ethoxymethylenepropane-1,3-dione (a compound II) and enabling the compound II to react with an aqueous solution of hydroxylamine hydrochloride and inorganic base in an organic solvent to prepare 5-cyclopropyl-4-[2-methylthio-4-(trifluoromethyl)benzoyl] isoxazole (a compound I). The total yield of two steps is greater than 90.0%, the content of 5-cyclopropyl-4-[2-methylthio-4-(trifluoromethyl)benzoyl] isoxazole is higher than the 98.0% and the content of impurity is less than 0.80%; and the preparation process has the advantages of simplicity in process, low cost, mild reaction conditions and less three wastes and is suitable for industrial production.