Sodium Hypochlorite → (3AR,5R)-5-((benzyloxy)methyl)-3a,4,5,7-tetrahydro-3H-pyrano[3,4-c]isoxazole

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An aqueous solution of sodium hypochlorite (14.5% solution, 600 mL) was added drop-wise to a 0° C. solution of 2-{[(2R)-1-(benzyloxy)pent-4-en-2-yl]oxy}-N-hydroxyethanimine (C3) (224 g from the previous step, ≦0.759 mol) in dichloromethane (1 L), while the internal temperature was maintained below 15° C. After completion of the addition, the reaction mixture was left to stir at 0° C. for 1.5 hours, then diluted with water (1 L) and dichloromethane (500 mL). The aqueous layer was extracted with dichloromethane (2×500 mL), and the combined organic layers were washed with saturated aqueous sodium chloride solution (500 mL), water (500 mL) and again with saturated aqueous sodium chloride solution (500 mL). They were subsequently dried over magnesium sulfate, filtered, and concentrated in vacuo. Purification via silica gel chromatography (Gradient: 0% to 25% ethyl acetate in heptane) afforded the product as a colorless oil. The indicated relative stereochemistry of compound P1 was assigned based on nuclear Overhauser enhancement studies, which revealed an interaction between the methine protons on carbons 3a and 5. Yield: 85.3 g, 345 mmol, 45% over 2 steps. LCMS m/z 248.1 [M+H+]. 1H NMR (400 MHz, CDCl3) δ 7.27-7.40 (m, 5H), 4.77 (d, J=13.5 Hz, 1H), 4.54-4.65 (m, 3H), 4.22 (dd, J=13.5, 1 Hz, 1H), 3.79 (dd, J=11.7, 8.0 Hz, 1H), 3.69-3.76 (m, 1H), 3.57 (dd, half of ABX pattern, J=10.1, 5.9 Hz, 1H), 3.49 (dd, half of ABX pattern, J=10.1, 4.3 Hz, 1H), 3.39-3.5 (m, 1H), 2.20 (ddd, J=12.9, 6.5, 1.6 Hz, 1H), 1.51-1.62 (m, 1H).

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