17-Chloro-16-formyl-Δ1,3,5(10)-estratetraen-3-ol 2a (100 mg, 0.32 mmol) was added to a suspension of acetamidine hydrochloride (150 mg, 1.3 mmol) and potassium carbonate (260 mg, 1.92 mmol) in DMF (4 mL). The mixture was stirred at 80°C for 8 h until the complete conversion of the intermediates (TLC monitoring). The resulting mixture was cooled to room temperature and diluted with water (30 mL). The precipitate that formed was filtered and washed with water (5 mL) and hot benzene (5 mL). The workup afforded the analytically pure product as colorless solid (40 mg, 32% yield). Rf 0.37 (petroleum ether:EtOAc, 1:2; visualized by UV light at 254 nm); m.p. 209–210°C. 1H NMR (600 MHz, DMSO-d6), δ: 0.84 (s, 3H, 18-CH3), 1.30–1.36 (m, 1H, 7-CH2), 1.37–1.50 (m, 3H, 8-CH, 11-CH2, 12-CH2), 1.58–1.62 (m, 1H, 14-CH), 1.75–1.83 (m, 2H, 7-CH2, 12-CH2), 1.80 (s, 3H, 4′-CH3), 1.82 (s, 3H, 6′-CH3), 1.95 (dd, J = 12.0, 14.4 Hz, 1H, 15-CH2), 2.14 (dd, J = 6.6, 14.4 Hz, 1H, 15-CH2), 2.18–2.22 (m, 1H, 9-CH), 2.31–2.36 (m, 1H, 11-CH2), 2.68–2.78 (m, 2H, 6-CH2), 5.35 (s, 1H, 2′-CH), 6.44 (d, J = 2.4 Hz, 1H, 4-CH), 6.51 (dd, 1H, J = 2.4, 9.0 Hz, 2-CH), 7.02 (d, 1H, J = 9.0 Hz, 1-CH), 9.03 (br.s, 1H), 9.37 (br.s, 1H). 13C NMR (150 MHz, DMSO-d6), δ: 15.0 (18-CH3), 20.2 (4′-CH3, 6′-CH3), 25.8 (11-CH2), 26.7 (7-CH2), 28.9 (15-CH2, 6-CH2), 33.6 (12-CH2), 36.9 (8-CH), 43.7 (9-CH), 47.9 (13-C), 53.1 (14-CH), 67.8 (2′-CH), 112.7 (2-CH), 115.0 (4-CH), 125.6 (1-CH), 130.2 (10-C), 135.4 (17-C), 137.0 (5-C), 138.6 (16-C), 151.6 (4′-C, 6′-C), 155.0 (3-C). IR (KBr), cm−1: 3198 (NH), 2929, 2857 (CH), 1703, 1611 (C = C, C = N), 1499, 1456, 1435, 1378, 1287, 1248. HRMS (ESI) for C23H29ClN3O ([M+H]+): calcd 398.1994, found 398.1995.