At 0° C., 1.0 g (3.7 mmol) of estrone (73) was dissolved in 50 mL of dry pyridine and 1.24 mL (7.4 mmol) of trifluoroacetic anhydride (Tf2O) was added slowly to the solution. After 1 h, the crude solution was poured into a cold aqueous solution of CuSO4 (1M) and the organic phase washed with the same solution until the blue color disappear. Next, the solution was extracted with EtOAc and the organic phase washed with water, and dried over MgSO4. After evaporation of the solvent, the crude estrone-triflate was dissolved in 50 mL of dry DMF. To the resulting mixture, we added 1.54 mL (11 mmol) of Et3N, 0.41 mL (11 mmol) of HCOOH, 0.143 mg (0.55 mmol) of PPh3, and 30.8 mg (0.14 mmol) of Pd(OAc)2. After 3 h at room temperature, the solution was quenched with aqueous HCl (5%) and extracted with CH2Cl2. The organic phase was washed with water, dried over MgSO4, and solvents evaporated to dryness. The crude compound was purified by flash chromatography with hexanes/EtOAc (9:1) as eluent to give 615 mg (65% two steps) of 1,3,5(10)-estratrien-17-one (74). White solid; IR ν (film): 1738 (C═O); 1H NMR (CDCl3) δ 0.94 (s, 3H, 18-CH3), 2.94 (m, 2H, 6-CH2), 7.16 (m, 3H, 1-CH, 2-CH, 3-CH), 7.32 (d, J=5.9 Hz, 1H, 4-CH); 13C NMR (CDCl3) δ 13.76 (C-18), 21.51 (C-15), 25.61 (C-11), 26.42 (C-7), 29.29 (C-6), 31.56 (C-12), 35.77 (C-16), 38.04 (C-8), 44.40 (C-9), 47.88 (C-13), 50.49 (C-14), 125.22 (C-3), 125.73 (C-2 and C-1), 128.98 (C-4), 136.37 (C-5), 139.62 (C-10), 220.63 (C-17).
