Reaction Steps
To a solution of methyl 4-((1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-3a-isocyanato-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)benzoate (610.0 mg, 1.071 mmol) in THF (10 mL) was added N,N-diisopropylethylamine (0.559 mL, 3.21 mmol) and N,N-dimethylethylenediamine (0.353 mL, 3.21 mmol). The reaction mixture was stirred at 25° C. After 18 h, the reaction mixture was diluted with EtOAc (50 mL) and treated with 1N HCl (5 mL). The mixture was concentrated to a paste and then triturated with EtOAc, filtered and washed with Et2O. The white solid was saved and the liquid filtrate was concentrated and the trituration and filtration steps were repeated twice more. The combined white solid product was dried in a vacuum oven to give the title compound (650.0 mg, 0.958 mmol, 90% yield). LCMS: m/e 658.4 (M+H)+, 4.25 min (method 8). 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 7.9 (2H, d, J=8.5 Hz), 7.2 (2H, d, J=8.2 Hz), 5.3 (1H, dd, J=6.3, 1.7 Hz), 4.8 (1H, s), 4.6 (1H, s), 3.9 (3H, s), 3.7-3.8 (1H, m), 3.5-3.6 (1H, m), 3.2 (2H, br. s.), 2.9 (6H, br. s.), 2.7-2.7 (1H, m), 2.6 (1H, d, J=13.4 Hz), 2.4 (1H, dd, J=11.6, 8.2 Hz), 2.1 (1H, dd, J=17.2, 6.3 Hz), 2.0-2.1 (1H, m), 1.8-1.9 (1H, m), 1.8 (1H, d, J=12.8 Hz), 1.7 (3H, s), 1.7 (1H, d, J=6.7 Hz), 1.6-1.7 (1H, m), 1.5-1.6 (2H, m), 1.5 (4H, d, J=2.7 Hz), 1.3-1.4 (5H, m), 1.2-1.3 (1H, m), 1.1 (3H, s), 1.0-1.1 (2H, m), 1.0 (3H, s), 1.0-1.0 (3H, m), 0.9 (6H, s). 13C NMR (CHLOROFORM-d) δ ppm 14.2, 15.8, 16.3, 18.4, 19.2, 19.5, 20.7, 21.1, 25.0, 27.1, 29.1, 29.5, 29.6, 33.3, 35.3, 35.4, 36.0, 37.2, 37.3, 40.3, 41.4, 41.7, 43.4, 46.7, 49.3, 51.7, 52.6, 53.4, 58.9, 63.9, 77.3, 109.8, 123.9, 127.6, 128.2, 129.8, 145.9, 148.5, 149.4, 157.5, 167.0.
