To a solution of 4-piperidyloxyamine dihydrochloride (III-a, Prepn. 1, 100 mg) and Na2HPO4.12H2O (380 mg) in water (1.6 mL), a solution of androstane-3,6,17-trione (160 mg) in THF (3.2 mL) was added. After 2 hours at room temperature, NaCl (150 mg) was added and stirred for 15 min. The mixture was extracted with THF (2×2 mL) and the combined organic phases were washed with brine (3×3 mL), dried over Na2SO4 and evaporated to dryness. The residue was purified by flash chromatography (SiO2, CH2Cl2:MeOH:NH3 9:1:0.1). To the concentrated fractions 5M HCl in EtOAc was added. After dilution with Et2O, the solid was collected by filtration to give the title compound I-aa (140 mg, 60%). 1H-NMR (300 MHz, DMSO-d6, ppm from TMS): δ 8.68 (2H, bb), 4.17 (1H, m), 3.15-2.90 (5H, m), 2.60-1.10 (23H, m), 0.79 (3H, s), 0.78 (3H, s).
