Benzenepropanal → 3-(2 (R)-cyclopentylmethyl-3(S)-hydroxyl-5-phenyl-1-oxopentyl)-4(R)-(phenylmethyl)-2-oxazolidinone

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To a solution of acyloxazolidinone 2 (1.57 g, 5.00 mmol) in 20 mL of dichloromethane, cooled to −78° C. under nitrogen atmosphere, dibutylboron triflate (1.40 mL, 5.50 mmol) was added dropwise, followed by the addition of triethylamine. The mixture was warmed slowly to 0° C. and was stirred at 0° C. for an additional hour. The resultant boryl enolate solution was then cooled to −78° C., and 3-phenylpropanal (0.80 mL, 5.5 mmol) was added over a 5-min period time. The solution was stirred for 1 h at −78° C., then for 1 h at 0° C. The reaction mixture was quenched by the addition of 4 mL of a pH 7 aqueous phosphate buffer and 12 mL of methanol. To this cloudy solution was added 8 mL of methanol and 10 mL of 30% aqueous hydrogen peroxide at such a rate as to keep the internal temperature below 10° C. After the solution was stirred for one additional hour, the volatile material was removed in a rotary evaporator. The resulting slurry was extracted with three 20 mL portions of diethyl ether. The combined organic layers was washed with 20 mL of 5% aqueous sodium bicarbonate and 20 mL of brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. Purification by flash column chromatography (25% ethyl acetate-hexane) provided 1.11 g (56%) of aldol 3 as a colorless oil. 1H NMR (300 MHz, CDCl3) δ 7.15-7.38 (m, 10 H), 4.72 (m, 1 H), 4.12-4.28 (m, 3 H), 3.85 (m, 1 H), 3.34 (1 H, dd, J=13.4, 3.1 Hz), 2.80-2.95 (1 H, m), 2.60-2.78 (2 H, m), 1.95-2.05 (1 H, m), 1.40-1.90 (10 H, m), 1.10 (2 H, m).

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