Oxalyl chloride (0.21 mL, 2.45 mmol) was dissolved in 5 mL dichloromethane and cooled to −78° C. The mixture was stirred for 15 minutes after 5 mL solution of dimethyl sulfoxide (0.24 mL, 3.26 mmol) in dichloromethane were added. Then 10 mL solution of [(2R,3R,4S,5R,6S)-3,4,5-tribenzyloxy-6-[4-chloro-3-[[4-(trifluoromethoxy)phenyl]methyl]phenyl]-6-methoxy-tetrahydropyran-2-yl]methanol 6m (1.22 g, 1.63 mmol) in dichloromethane were added before the mixture was stirred for 40 minutes. Then the reaction mixture was warmed and stirred for 1.5 hours at room temperature after triethylamine (1.18 mL, 8.15 mmol) was added and partitioned after 10 mL 1 M hydrochloric acid were added. The organic extract was washed with saturated sodium chloride solution (10 mL×2) and combined, dried over anhydrous magnesium sulfate, and filtered. The filtrate was concentrated under reduced pressure to obtain the title compound (2S,3S,4S,5R,6S)-3,4,5-tribenzyloxy-6-[4-chloro-3-[[4-(trifluoromethoxy)phenyl]methyl]phenyl]-6-methoxy-tetrahydropyran-2-carbaldehyde 6n (1.21 g, yellow grease), which was used directly in the next step without purification.
