Triethylamine → (1R,3aS,5aR,5bR,7aR,11aR,11bR,13aR,13bR)-3a-isocyanato-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)octadecahydro-1H-cyclopenta[a]chrysen-9(5bH)-one

Participants

Reaction Steps

To a solution of (1R,3aS,5aR,5bR,7aR,11aR,11bR,13aR,13bR)-5a,5b,8,8,11a-pentamethyl-9-oxo-1-(prop-1-en-2-yl)icosahydro-1H-cyclopenta[a]chrysene-3a-carboxylic acid (16.41 g, 36.1 mmol) in 1,4-dioxane (200 mL) was added triethylamine (15.09 mL, 108 mmol) and diphenyl phosphorazidate (11.67 mL, 54.2 mmol). The mixture was heated to reflux for 18.5 h, then was cooled to rt and concentrated under reduced pressure. The residue was split into two portions and was purified using a 0-15% ethyl acetate in hexanes gradient and a Thomson 240 g silica gel column to purify each portion. The fractions containing the expected product were combined and concentrated under reduced pressure to give (1R,3aS,5aR,5bR,7aR,11aR,11bR,13aR,13bR)-3a-isocyanato-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)octadecahydro-1H-cyclopenta[a]chrysen-9(5bH)-one (10.3 g, 22.80 mmol, 63.2% yield) as an off-white foam. 1H NMR (400 MHz, chloroform-d) δ=4.75 (d, J=2.0 Hz, 1H), 4.66-4.63 (m, 1H), 2.60-2.36 (m, 4H), 2.17-2.04 (m, 1H), 1.69 (s, 3H), 1.10 (s, 3H), 1.08 (s, 3H), 1.04 (s, 3H), 0.95 (s, 6H), 2.01-0.71 (m, 20H).

Provenance & Evidence