Ethyl Acetate → (+)-Betulonic acid

Participants

Reaction Steps

To a chilled solution of (1R,3 aS,5aR,5bR,7aR,9S,11aR,11bR,13 aR,13bR)-9-hydroxy-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)icosahydro-1H-cyclopenta[a]chrysene-3a-carboxylic acid (2.35 g, 5.15 mmol) in DMF (45 mL) at ˜4° C. under nitrogen was added pyridinium dichromate (PDC 3.87 g, 10.29 mmol) in a single portion. The suspension was rapidly stirred, forming an orange solution, but rapidly changed into dark brownish with all the PDC dissolved into the reaction mixture. The reaction was kept in an ice bath, and was allowed to warm to RT slowly over 8 hours. Stirring continued for 48 hrs at RT thereafter. The PDC reaction mixture acquired a dull dark brownish appearance but no PPT was observed. The crude DMF reaction solution was poured into vigorously stirred ethyl acetate (400 mL) causing a PPT of a light brownish solid. The suspension was filtered through a short bed (˜1″ thick) of silica gel type-H in a large diameter filter funnel. The clear filtrate was washed with 0.1 N HCl (200 mL), then with water (3×200 mL). All the volatile solvents were removed, giving 2.1 gm (88%) as a white solid. MS: m/e 477.21 (M+Na)+, 6.2 min (method 9). 1H NMR (400 MHz, CHLOROFORM-d) δ 4.76 (d, J=2.3 Hz, 1H), 4.63 (s, 1H), 3.06-2.98 (m, 1H), 2.55-2.37 (m, 2H), 2.28 (s, 2H), 1.99 (d, J=6.5 Hz, 2H), 1.95-1.87 (m, 1H), 1.71 (s, 3H), 1.64 (t, J=11.4 Hz, 2H), 1.59-1.20 (m, 16H), 1.08 (s, 3H), 1.03 (s, 3H), 1.00 (s, 3H), 0.99 (s, 3H), 0.94 (s, 3H).

Provenance & Evidence