A solution of (R)-4-benzyl-3-propionyl-2-oxazolidinone (2.18 g, 9.34 mmol) and methylene chloride (15 mL) is cooled to −20° C. (n-Bu)2BOTf (1.0 M in DCM, 8.7 mL, 8.7 mmol) is introduced dropwise. The reaction is allowed to warm to 0° C. NEt3 (1.15 9, 11.34 mmol) is added and the mixture is stirred at 0° C. for 1 h, then cooled to −78° C. A solution of (2R,3S,4S,5Z)-3-[(4-methoxyphenyl)methoxy]-2,4-dimethyl-5,7-octadienal (1.95 g, 6.77 mmol) in DCM (10 mL) is added dropwise at −70° C. for 10 min. After 1 h at −74° C., the mixture is warmed to 0° C. The reaction is quenched with pH 7 buffer (15 mL). The mixture is slowly treated with a solution of 30% H2O2 in MeOH (1:2, 15 mL) at 0° C., stirred for 40 min at room temperature, and concentrated. The residue is extracted with ethyl acetate (3×100 mL). The combined organic phase is washed with saturated aqueous NaHCO3, brine, and concentrated. Flash chromatography gives the desired compound (3.4 g, 96.4%) as a clear oil.
