Reaction Steps
To a solution of the SEM protected thioglycoside 79 (1.60 g, 2.73 mmol) in 15 mL of methanol is added sodium methoxide (300 mg, 5.56 mmol). The mixture is stirred at room temperature for 12 h, then neutralized with Amberlite resin (acid form), filtered, concentrated and run through a short column of silica gel (10% MeOH/EtOAc) to provide crude 1-deoxy-1-{4-[2-(trimethylsilyl)ethoxymethoxy]phenylthio}-β-D-galactopyranose 80 as an oil: Rf 0.15 (EtOAc). The material is taken up in 10 mL of DMF, and dimethoxypropane (0.59 mL, 4.8 mmol), and p-toluenesulfonic acid hydrate (90 mg, 0.48 mmol) are added. The mixture is stirred at room temperature for 12 h, pyridine (0.04 mL, 0.48 mmol) is added, and the reaction mixture is concentrated and purified by flash chromatography (60% EtOAc/hexane) to give 0.5 g (41%) of 1-deoxy-3,4-O-isopropylidene-1-{4-[2-(trimethylsilyl)ethoxymethoxy]phenylthio}-β-D-galactopyranose 81 as a colorless oil: Rf 0.5 (67% EtOAc/hexane); 1H NMR (CDCl3, 300 MHz) δ 7.48 (d, J=8.6 Hz, 2H), 6.99 (d, J=8.6 Hz, 2H), 5.21 (s, 2H, SEM), 4.35 (d, J=10.2 Hz, 1H, H-1), 4.17 (dd, J=1.7, 5.4 Hz, 1H), 4.09 (dd, J=6.5 Hz, 1H), 3.94 (m, 1H), 3.85 (m, 2H), 3.73 (t, J=8.1 Hz, 2H, SEM), 3.52 (m, 1H), 2.49 (d, J=1.8 Hz, 1H), 2.17 (d, J=9.1 Hz, 1H), 1.40 (s, 3H, Me), 1.33 (s, 3H, Me), 0.93 (t, J=8.1 Hz, 2H, CH2 --TMS), 0.01 (s, 9H, SiMe3).
