Betulin → Betulonal

Participants

Reaction Steps

To suspension of (1R,3aS,5aR,5bR,7aR,9S,11aR,11bR,13aR,13bR)-3a-(hydroxymethyl)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)icosahydro-1H-cyclopenta[a]chrysen-9-ol (20 g, 45.2 mmol) in acetonitrile (200 mL) and DCM (300 mL) was added 4 angstrom molecular sieves (5 g) and the mixture was stirred for 10 minutes at rt. To the mixture was then added NMO (15.88 g, 136 mmol) and TPAP (0.794 g, 2.259 mmol). The dark green mixture was stirred under nitrogen overnight. Additional NMO (2.0 g) and TPAP (0.08 g) were added and the mixture was stirred at rt for 7 h. The mixture was filtered through a pad of silica gel and celite which was washed with dichloromethane then 25% EtOAc in hexanes. The filtrate was concentrated under reduced pressure and purified using a Thomson 240 g silica gel column and a 15-20% ethyl acetate in hexanes gradient. The title product was isolated as a white foam (17.6 g, 40.1 mmol, 89%). 1H NMR (400 MHz, chloroform-d) δ=9.68 (d, J=1.5 Hz, 1H), 4.77 (d, J=2.0 Hz, 1H), 4.66-4.63 (m, 1H), 2.89 (td, J=11.2, 5.8 Hz, 1H), 2.56-2.36 (m, 2H), 2.16-2.03 (m, 2H), 1.97-1.84 (m, 2H), 1.71 (s, 3H), 1.08 (s, 3H), 1.03 (s, 3H), 1.00 (s, 3H), 0.97 (s, 3H), 0.94 (s, 3H), 1.83-0.87 (m, 18H).

Provenance & Evidence