The invention discloses a method for preparing a
vitamin D2 derivative. In the conventional method for preparing
Calcipotriol, C-24 hydroxy epimeric
alcohol (a compound III) is mainly obtained, the yield of the
Calcipotriol is greatly reduced, and the C-24 hydroxy epimeric
alcohol is a waste intermediate and does not have any utilization value so far. In the method of the invention, the waste intermediate compound III generated in the conventional process of preparing the
Calcipotriol is taken as a starting material, and the method comprises the following steps of: in an
organic solvent and in the presence of an oxidizer capable of oxidizing hydroxyl into carbonyl, performing heat preservation reaction at the temperature of between 20 and 120 DEG C, after complete reaction, cooling to
room temperature, and treating to obtain a compound I; and performing reduction reaction on the compound I to obtain a compound II, namely the Calcipotriol. In the method, the waste intermediate compound III is recycled, the cost of raw materials is low, the
utilization rate of the materials is improved, and the
pollution is reduced; and by combining the conventional preparation process, the method can obviously improve the yield of the Calcipotriol in the conventional preparation process.