To a suspension of 3-benzyloxy-2-aminoestra-1,3,5(10)-trien-17-one (80, 0.751 g, 2.0 mmol) in THF (2.0 mL) and CH3CN (10 mL) were added 37% aqueous formaldehyde (4.0 mL) and sodium cyanoborohydride (0.377 g, 6.0 mmol) and stirred for 2 h at room temperature. Additional sodium cyanoborohydride (0.377 g, 6.0 mmol) was then added to the reaction mixture, which mixture was then stirred for 20 h. Next, saturated aqueous NH4Cl at 0° C., was added to the reaction mixture, and it was then extracted with EtOAc. The combined organic layers were washed with H2O, saturated aqueous NaCl, and then dried (Na2SO4). The desiccant was filtered and the solvent was evaporated at reduced pressure. The residue was purified by column chromatography (silica gel) using n-hexane:THF (5:1→3:1, v/v) to afford 0.797 g of 81 (99% yield) mp: 165-166° C.
