Triethylamine → 3alpha-isocyanato-1-isopropenyl-5alpha,5beta,8,8,11alpha-pentamethylicosahydro-1H-cyclopenta[a]chrysen-9-ol

Beteiligte Stoffe

Reaktionsschritte

To a suspension of betulinic acid (10 g, 21.90 mmol) in 1,4-Dioxane (100 mL) was added triethylamine (9.16 mL, 65.7 mmol) and diphenyl phosphorazidate (7.08 mL, 32.8 mmol). The mixture was heated to reflux. Upon heating, all solids dissolved. After heating the mixture for 26 h, the mixture was cooled to rt and was concentrated under reduced pressure. The residue was diluted with 100 mL of water and was extracted with dichloromethane (3×100 mL). The combined organic layers were dried with sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure. The residue was purified by flash chromatography in silica gel using a 0-15% EtOAc in hexanes gradient and a Thomson 240 g silica gel column. The fractions containing the expected product were combined and concentrated under reduced pressure. A second batch of less-pure product was concentrated and was repurified using a Thomson 240 g column and the same gradient The fractions containing the expected product were combined with the first batch to give (1R,3aS,5aR,5bR,7aR,9S,11aR,11bR,13aR,13bR)-3a-isocyanato-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)icosahydro-1H-cyclopenta[a]chrysen-9-ol (7.76 g, 17.10 mmol, 78% yield) as a white solid. 1H NMR (400 MHz, chloroform-d) δ=4.75 (s, 1H), 4.67-4.62 (m, 1H), 3.20 (dt, J=11.3, 5.6 Hz, 1H), 2.55 (td, J=10.9, 5.9 Hz, 1H), 2.17-2.03 (m, 1H), 1.92-1.76 (m, 5H), 1.69 (s, 3H), 1.06 (s, 3H), 0.98 (s, 3H), 0.95 (s, 3H), 0.85 (s, 3H), 0.78 (s, 3H), 1.74-0.66 (m, 19H).

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