A mixture of (R)-4-benzyl-3-pent-4-enoyloxazolidin-2-one (50 g, 193 mmol), magnesium chloride (18.3 g, 193 mmol), sodium hexafluorostibate(V) (14.9 g, 58 mmol), triethylamine (80 mL, 579 mmol), (trans)-cinnamaldehyde (30.6 g, 232 mmol) and chlorotrimethylsilane (37.2 mL, 290 mmol) in ethyl acetate (500 mL) was stirred at room temperature for 17 hours. The mixture was diluted with ethyl acetate and filtered to remove solids. The filtrate was concentrated to small volume, and then diluted with methanol (500 mL) and a small amount of ethyl acetate. After treatment with trifluoroacetic acid (3 mL), the resulting solution was stirred at room temperature for 1 h, and then concentrated to dryness under reduced pressure. The residue was purified by silica gel column chromatography (ethyl acetate:petroleum ether=1:10) to afford the title compound (60 g, 80%) as a yellow semi-solid. MS (ES+) C24H25NO4 requires: 391, found: 374 [M+H−H2O]+.
