[CH:1]([O:8][CH2:9][CH3:10])(OCC)OCC.C(O[C@@H:15]1[C@H:21]2[C@H:22]3[C@H:31]([CH2:32][CH2:33][C@:18]2([CH2:19][CH3:20])[C:17](=[O:35])[CH2:16]1)[C@@H:30]1[C:25](=[CH:26]C(=O)[CH2:28][CH2:29]1)[CH2:24][CH2:23]3)(=O)C.N.C(OCC)(=O)C>CCO.C1(C)C=CC(S(O)(=O)=O)=CC=1.O>[CH2:9]([O:8][C:1]1[CH2:28][CH2:29][C@H:30]2[C:25](=[CH:24][CH2:23][C@@H:22]3[C@@H:31]2[CH2:32][CH2:33][C@@:18]2([CH2:19][CH3:20])[C@H:21]3[CH:15]=[CH:16][C:17]2=[O:35])[CH:26]=1)[CH3:10]
Triethyl orthoformate (3 ml, 18 mmol) and p-Toluenesulfonic acid (30 mg, 0.16 mmol) were added to a suspension of 15α-acetoxy-18-methyl-estr-4-en-3,17-dione (3 g, 8.8 mmol) in EtOH (18 ml). The mixture was stirred at room temperature for 1 h. Ammonia 32% (15.4 ml, 145 mmol) was added, and the mixture was heated at 40° C. for 48 h, cooled to 10° C., and ethyl acetate and water (15 ml) were then added. The extract was washed with water and concentrated. The crude product was purified by flash chromatography, eluting with heptane and ethyl acetate (8:2), crystallized from heptane, and dried under vacuum to afford 3-ethoxy-18-methyl-estra-3,5,15-trien-17-one (1.54 g, yield: 56%).
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