Preparation method for Dapagliflozin

The invention relates to a preparation method for Dapagliflozin. The preparation method comprises the following steps that a compound 2 and phenetole are mixed to obtain a mixture, and then the mixture is dropped into a suspended aluminum trichloride solution, so that the content of generated ortho isomer impurities is smaller than 1 percent; a compound 4 in the preparation method is firstly reacted with butyl lithium to generate a compound 5 in the following formula; then the compound 5 is reacted with a compound 1, so that generation of sulphonate type genetic toxic impurities is avoided; therefore the utilization rate of raw materials is increased to a certain extent, the problem of complicated post-treatment is avoided, and the purity and the yield of products are improved. According to the preparation method, a compound 6 is reduced by using hydroboron and sulfuric acid, so that the reduction reaction and deprotection can be simultaneously carried out, and the pollution is greatly alleviated. The raw materials and the reagents which are adopted in the preparation method are relatively cheap and low in cost; meanwhile, the reaction conditions of the whole preparation process are mild, and the operation is simple and safe; industrial production can be conveniently realized.