[CH3:1][O:2][C:3]1[CH:20]=[CH:19][C:18]2[C@@H:17]3[C@H:8]([C@@H:9]4[C@@:13]([CH2:15][CH2:16]3)([CH3:14])[C@H:12]([CH2:21][OH:22])[CH2:11][CH2:10]4)[CH2:7][CH2:6][C:5]=2[CH:4]=1.CC(O)C.O>CS(C)=O.C(N(CC)CC)C>[CH3:1][O:2][C:3]1[CH:20]=[CH:19][C:18]2[C@@H:17]3[C@H:8]([C@@H:9]4[C@@:13]([CH2:15][CH2:16]3)([CH3:14])[C@H:12]([CH:21]=[O:22])[CH2:11][CH2:10]4)[CH2:7][CH2:6][C:5]=2[CH:4]=1i)—A solution of sulfur trioxide pyridine complex (50.0 g) in dimethyl sulfoxide (250 ml) was added in 15 min. to a solution of (14β,17α)-3-methoxyestra-1,3,5(10)-triene-17-methanol (Example 1, step ii; 23.6 g) in a mixture of dimethyl sulfoxide (425 ml) and triethylamine (70 ml). After 20 min. stirring, 2-propanol (88 ml) was added and stirring was continued for 15 min. The reaction mixture was poured into water (1300 ml) and the product was extracted into dichloromethane. The combined organic phases were washed with water and brine, dried over magnesium sulfate and concentrated under reduced pressure. Trituration (water/ethanol, first 3:2, then 1:1) afforded (14β,17α)-3-methoxyestra-1,3,5(10)-triene-17-carboxaldehyde (18.8 g).
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