The incubation of 11-methyleneestr-4-ene-3,17-dione (I) with spores of Gomerella cingulata (ATCC 10534) gives 15-alpha-hydroxy-11-methyleneestr-4-ene-3,17-dione (II), which is treated with ethane-1,2-dithiol and borontrifluoride ethearate in ethanol yielding the 3-dithioacetal (III). The reaction of (III) with methanesulfonyl chloride, followed by elimination with sodium acetate affords 11-methyleneestra-4,15-diene-3,17-dione 3-(ethylenedithioacetal) (IV), which is treated with potassium acetylide (V) in THF to afford the 17-alpha-ethynyl-17-beta-hydroxy derivative (VI). Finally, this compound is deprotected by a treatment with K2CO3 and methyl iodide in refluxing methanol/water.