18-Methyl-4-oestrene-3,17-dione (I) is hydroxylated by fermentation with Penicillium raistrickii giving the 15alpha-hydroxy compound (II), which is ketalized with 2,2-dimethylpropanediol (A), triethyl orthoformate and p-toluenesulfonic acid in CH2Cl2 giving a mixture of the DELTA(5-6) and DELTA(5-10)-ketals (IIIa-b). These ketals are mesylated witn methanesulfonyl chloride in pyridine yielding the mesyl ester (IVa-b), which is treated with sodium acetate in DMF to afford the oestradiene ketal (Va-b). Finally, this compound is treated with ethynylmagnesium bromide (B) and refluxed with oxalic acid (C) in methanol.
Ketals (IIIa-b) can also be treated with trimethylsilyl chloride in pyridine to give the trimethylsilyl derivative (VIa-b), which is then treated with ethynylmagnesium bromide (B) and oxalic acid (C) in methanol.
Ketals (IIIa-b) can also be acetylated with acetic anhydride in pyridine to the acetate (VIIa-b), which is then treated with ethynylmagnesium bromide (B) and oxalic acid (C) in methanol.