反応手順
To a solution of (1R,3aS,5aR,5bR,7aR,11aR,11bR,13aR,13bR)-3a-((tert-butoxycarbonyl)amino)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1H-cyclopenta[a]chrysen-9-yl trifluoromethanesulfonate (0.2 g, 0.304 mmol) in dichloromethane (2 mL) was added trifluoroacetic acid (0.5 mL, 6.49 mmol). The mixture was stirred at rt for 1.5 h then was concentrated under reduced pressure. The residue was diluted with saturated aqueous sodium bicarbonate (20 mL) and extracted with dichloromethane (3×20 mL). The combined organic layers were dried with sodium sulfate. The drying agent was removed by filtration. The filtrate was concentrated and adsorbed to silica gel and purified using a 12-100% ethyl acetate in hexanes gradient and a 12 g Thomson silica gel column. The fractions containing the expected product were combined and were concentrated under reduced pressure to give (1R,3aS,5aR,5bR,7aR,11aR,11bR,13 aR,13bR)-3a-amino-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1H-cyclopenta[a]chrysen-9-yl trifluoromethanesulfonate (0.109 g, 0.195 mmol, 64.3% yield) as an off-white solid. 1H NMR (500 MHz, chloroform-d) δ=5.57 (dd, J=6.8, 1.9 Hz, 1H), 4.73 (d, J=1.6 Hz, 1H), 4.63-4.60 (m, 1H), 2.54 (td, J=10.9, 5.3 Hz, 1H), 2.17 (dd, J=17.1, 6.9 Hz, 1H), 2.08-1.99 (m, 1H), 1.70 (s, 3H), 1.13 (s, 3H), 1.08 (s, 3H), 1.03 (s, 3H), 0.97 (s, 3H), 0.93 (s, 3H), 1.82-0.91 (m, 20H).
