Reaktionsschritte
To a slurry of (1R,3aS,5aR,5bR,7aR,11aS,11bR,13aR,13bR)-9-(4-(methoxycarbonyl)phenyl)-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]chrysene-3a-carboxylic acid (10 g, 17.46 mmol) in 1,4-dioxane (200 mL) was added triethylamine (4.38 mL, 31.4 mmol) followed by diphenyl phosphoryl azide (5.82 mL, 26.2 mmol). The resulting white slurry was heated to 100° C. After 5 h, the reaction was allowed to cool to rt and was then diluted with EtOAc and washed with 1N NaOH (2×70 mL). The combined aqueous layer was extracted with EtOAc (2×150 mL). The combined organic layer was dried over Na2SO4, filtered and concentrated to slurry (about 75 mL) which was stored in a refrigerator overnight. The slurry was filtered and the white solid product was washed with Et2O. The liquid filtrate was concentrated to yellow slurry which was filtered and washed with Et2O to give more white solid product. The two batches of white solid were combined and dried under reduced pressure to give 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 (8.6 g, 86% yield) as a white solid. 1H NMR (500 MHz, CHLOROFORM-d) δ ppm 8.0 (2H, d, J=8.2 Hz), 7.2 (2H, d, J=8.2 Hz), 5.3 (1H, d, J=4.6 Hz), 4.8 (1H, s), 4.7 (1H, s), 3.9 (3H, s), 2.6 (1H, td, J=10.8, 5.8 Hz), 2.1-2.2 (2H, m), 1.8-2.0 (4H, m), 1.7-1.8 (1H, m), 1.7 (3H, s), 1.5-1.7 (5H, m), 1.4-1.5 (5H, m), 1.3-1.4 (2H, m), 1.2-1.3 (2H, m), 1.1 (3H, s), 1.1-1.1 (1H, m), 1.0 (3H, s), 1.0 (3H, s), 1.0 (3H, br. s.), 1.0 (3H, br. s.). 13C NMR (CHLOROFORM-d) δ ppm 14.2, 15.4, 16.2, 19.2, 19.5, 20.8, 21.0, 24.7, 27.4, 29.0, 29.2, 33.3, 36.0, 37.2, 39.0, 39.0, 40.3, 41.5, 41.8, 47.8, 49.0, 49.2, 51.7, 52.6, 66.8, 71.3, 110.2, 121.3, 123.7, 127.6, 128.2, 129.8, 146.0, 148.4, 148.6, 166.9.
