m-Chloroperbenzoic acid → [(S)-2-((R)-8-Hydroxymethyl-7,8-dihydro-[1,4]dioxino[2,3-g]indazol-1-yl)-1-methyl-ethyl]-carbamic acid benzyl ester

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To a stirred solution of the epoxide from Step A (0.86 g, 2.10 mmol) in dichloromethane (100 mL) was added m-chloroperbenzoic acid (70%, 0.62 g, 2.52 mmol) in portions under nitrogen atmosphere. After the addition completed the reaction mixture was stirred overnight. The reaction was quenched by a saturated aqueous solution of sodium thiosulfate (20 mL) and dichloromethane was evaporated. To the aqueous residue was added potassium carbonate (1.0 g) and methanol (200 mL), the resulting mixture was stirred for ½ h and organic solvent was evaporated. The residue was extracted with ethyl acetate (50 mL×3), dried and evaporated to dryness to afford an oil. Chromatography on silica eluting with a gradient of 0% to 10% acetone/dichloromethane gave an oil (0.50 g, 60%). LCMS (+APCI) m/z 397 (M+H), 1H NMR (600 MHz, CDCl3) δ 7.82 (s, 1H), 7.33-7.13 (m, 5H), 7.14 (d, J=8.4 Hz, 1H), 6.74 (d, J=8.4 Hz, 1H), 5.04-4.97 (m, 3H), 4.65 (ddd, J=6.6, 13.4, 51.6 Hz, 2H), 4.32 (m, 3H), 4.08 (m, 2H), 3.91 (m, 2H), 1.18(d, J=7.2 Hz, 3H).

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