[OH:1][CH:2]1[CH2:7][CH2:6][CH2:5][CH2:4][CH:3]1[NH:8][C:9](=[O:18])[O:10][CH2:11][C:12]1[CH:17]=[CH:16][CH:15]=[CH:14][CH:13]=1.CC(C)=O.OS(O)(=O)=O.O=[Cr](=O)=O>OS(O)(=O)=O.O.CC(C)=O>[O:1]=[C:2]1[CH2:7][CH2:6][CH2:5][CH2:4][CH:3]1[NH:8][C:9](=[O:18])[O:10][CH2:11][C:12]1[CH:13]=[CH:14][CH:15]=[CH:16][CH:17]=1A mixture of CrO3 (0.70 g) in concentrated H2SO4 (0.61 mL) was diluted with H2O to the volume of 6 mL. To a solution of benzyl 2-hydroxycyclohexylcarbamate (1.60 g, 6.43 mmol) in acetone (5.4 mL) at 0° C. was added Jones Reagent (5.51 mL, 1.17 M, 6.43 mmol) dropwise over 5 min. The reaction mixture was stirred at room temperature for 1.5 h, quenched with 20% aq. K2CO3 to pH=8. The aqueous layer was extracted with EtOAc (3×15 mL). The combined organic layers were washed with sat. NaCl (20 mL), dried over Na2SO4, filtered and concentrated. The resulted crude yellow oil was purified by ISCO chromatography (40 g column) using hexanes/EtOAc (0-30% over 8 min, 30-45% over 10 min) to give benzyl 2-oxocyclohexylcarbamate as a colorless oil at a retention time of 8.5-11 min (1.26 g, 79% yield). HPLC: RT=2.69 min, Purity 99% (Phenomenex Luna C18 column, 4.6×50 mm eluting with 10-90% MeOH/H2O over 4 minutes containing 0.2% PPA; 4 mL/min, monitoring at 220 nm). NMR: 400 MHz 1H (CDCl3) 7.33 ppm, 5H, m; 5.76 ppm, 1H, s; 5.11 ppm, 2H, m; 4.27 ppm, 1H, m; 2.65 ppm, 1H, dd, J=6.60, 2.75 Hz; 2.52 ppm, 1H, m; 2.38 ppm, 1H, m; 2.13 ppm, 1H, m; 1.89 ppm, 1H, m; 1.77 ppm, 1H, m; 1.64 ppm, 1H, m; 1.42 ppm, 1H, m.
Loading…
