Reaction Steps
To a solution of 6 (5.25 g, 11.57 mmol) in anhydrous methanol (50 mL) and under nitrogen was added a catalytic amount of sodium methoxide. After 5 hours at room temperature, the reaction mixture was neutralized with resin IR 120 (H+), filtered, and the solvent was evaporated. The resulting p-methoxyphenyl β-D-galactopyranoside 7 was used without any further purification and characterization. Compound 7 (3.24 g, 11.34 mmol) in solution in anhydrous methanol (50 mL) and under nitrogen was reacted with dibutyltin oxide (3.11 g, 12.48 mmol). After 4 hours at reflux, the reaction mixture was concentrated under vacuum. The dried residue was suspended in toluene (80 mL) and treated with allyl bromide (1.17 mL, 13.61 mmol) and tetrabutylammonium iodide (4.17 g, 11.34 mmol). The suspension was stirred under nitrogen at 60° C. for 18 h. TLC of the resulting brownish solution showed the presence of 50% of unreacted starting material. This solution was reacted with additional allyl bromide (0.58 mL, 6.80 mmol). After 18 hours at 60° C., the solvent was evaporated and the residue was purified by chromatography on silica gel (ethyl acetate) to afford 8 in 85% yield (3.16 g), isolated as yellowish crystals. Recrystallization of 8 in ethyl acetate afforded white crystals. mp=140-141° C.; [αD]23 =−8° (c 1, CHCl3); 1H NMR (500 MHz, CD3OD): δ3.32 (m, 1H, H-5), 3.39 (dd, 1H, J2,3 9.5 Hz, J3,4 3.2 Hz, H-3), 3.58 (t, 1H, J5,6b 6.1 Hz, J6a,6b 6.0 Hz, H-6b), 3.75 (s, 3H, OMe), 3.78 (dd, 1H, J5,6a 4.8 Hz, H-6a), 3.86 (dd, 1H, J1,2 7.9 Hz, H-2), 4.07 (d, 1H, J4,5<1.5 Hz, H-4), 4.17 and 4.26 (2 dd, 1H each, OCH2), 4.74 (d, 1H, H-1), 5.18 and 5.34 (2 dd, 1H each, CH═CH2), 6.00 (m, 1H, CH═CH2), 6.80 and 7.08 (2 d, 2H each, Ph). Anal. Calcd for C16H22O7 (326.3): C 58.89, H 6.79; found: C 58.37, H 6.91.
