Preparation method of drug intermediate

The invention provides a preparation method of a drug intermediate. The preparation method comprises the following steps: reducing a compound shown as a formula II (shown in the specification) in the presence of a boric reagent and (-) alpha-pinene, and carrying out oxidation by virtue of hydrogen peroxide to produce a compound shown as a formula I (shown in the specification), wherein R is alkyl or aryl group substituted methyl of C1-C6, preferably R is methyl, tert-butyl or diphenylmethyl; the boric reagent is borane, a single reagent or a mixed reagent of borane produced by sodium borohydride or potassium borohydride and inorganic acid such as concentrated sulfuric acid or Lewis acid such as boron trifluoride on the spot or a compound of the reagent or the mixed reagent and a solvent such as dimethyl sulfide or tetrahydrofuran. According to the preparation method provided by the invention, in the presence of the boric reagent and the (-) alpha-pinene, the alpha-pinene boric reagent can be produced in reaction, and the stereoselectivity is high in the process of reducing the compound shown as the formula II; in addition, with the (-) alpha-pinene as a raw material, the preparation method of the compound shown as the formula I is economical, is capable of saving the cost is suitable for industrialization.