Hydrochloric Acid → (2S,3aS,4R,9bR)-4-(4-Hydroxy-phenyl)-2-methyl-1,2,3,3a,4,9b-hexahydro-cyclopenta [c]chromen-8-ol

Participants

Reaction Conditions

Reaction Steps

To a solution of [2-(2,5-bis-methoxymethoxy-phenyl)-4-methyl-cyclopentyl]-(4-methoxymethoxy-phenyl)-methanone 10a (2.6 g, 5.8 mmol) in anhydrous methanol (232 mL) add p-toluenesulfonic acid (1.1 g, 5.8 mmol) and heat the resulting solution to 50° C. for 18 hours under nitrogen. Cool the reaction to ambient temperature and add bromocreosol green (10 mg) and sodium cyanoborohydride (1.82 g, 29.0 mmol). Add methanol saturated with HCl (gas) drop wise until yellow color is maintained. Stir the reaction one hour past the time when no more color change is observed. Quench the reaction with saturated sodium bicarbonate, add EtOAc, and wash the organic solution with sodium bicarbonate and brine. Dry the organic solution over sodium sulfate, concentrate in vacuo, and purify by flash chromatography (silica gel, 0-40% EtOAc/hexanes and 40% ethyl acetate/hexanes) to give 4-(4-Hydroxy-phenyl)-2-methyl-1,2,3,3a,4,9b-hexahydro-cyclopenta[c]chromen-8-ol 11a (1.2 g, 4.0 mmol, 70%). 1H NMR (δ, 400 MHz, MeOD) 7.23 (d, 2H, J=8.4 Hz), 6.77 (d, 2H, J=8.4 Hz), 6.68 (d, 1H, J=8.8 Hz), 6.54 (d, 1H, J=2.6 Hz), 6.50 (dd, 1H, J=8.6, 2.9 Hz), 3.45-3.38 (m, 1H), 2.63-2.55 (m, 1H), 2.52-2.43 (m, 1H), 1.96-1.84 (m, 1H), 1.41-1.32 (m, 1H), 1.23-1.07 (m, 2H), 0.87 (d, 3H, J=6.6 Hz). MS calcd. 295.1; found (electrospray, M−1) 295.1. HPLC (Zorbax C18 column; 10 to 100% CH3CN/H2O for 10 min then 100% CH3CN for 5 min; 1 mL/min; tr 10.35 min). HPLC (Chiralpak AD, 20-80% IPA/Heptane for 20 min; 1 mL/min; tR=4.37 min).

Provenance & Evidence