1) Add 5.0 g of pregnane-1,4,16-triene-3,11,20-trione (compound (I-1)) with 0.02 times copper bromide dimethyl sulfide, 1.2 times trimethylchlorosilane, 2 times hexamethylphosphorotriamine to 60 ml of tetrahydrofuran, and slowly add 1.2 times methylmagnesium bromide dissolved in the tetrahydrofuran to carry out the Grignard reaction, the temperature of the reaction is -30-20. The reaction was protected by passing N2, and at the end of the reaction it was diluted with water, separated and dried to obtain the Grignard product (compound (II-1));
2) React the above Grignard with 3 times potassium bicarbonate and 1.5 times m-chloroperoxybenzoic acid in dichloromethane at a reaction temperature of -30 to -25C, and react until complete. The solution pH was adjusted to 1 with hydrochloric acid, concentrated under reduced pressure, cooled, separated and dried to obtain the compound dexamethasone EP impurity J(III-1), total yield 78.2%.
