To a solution of (2S,3S,4S,5R,6S)-3,4,5-tribenzyloxy-6-[4-chloro-3-[[4-(trifluoromethoxy) phenyl]methyl]phenyl]-6-methoxy-tetrahydropyran-2-carbaldehyde 15l (100 mg, 0.13 mmol) in tetrahydrofuran (5 mL) were added formaldehyde (72.3 mg, 2.47 mmol, 37 wt % solution) and 1,8-diazabicyclo[5.4.0]undec-7-ene (16.3 mg, 0.11 mmol) in turn at room temperature. The mixture was stirred at room temperature for 48 hours, and then ethyl acetate (20 mL) and water (5 mL) were added. The resulting mixture was partitioned. The aqueous layer was extracted with ethyl acetate (10 mL×2). The combined organic layers were washed with saturated aqueous sodium chloride (10 mL×2), dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo to give the title compound 15m as yellow oil (108 mg, 100%). This material was not further purified.
