Reaction Steps
Thioglycoside 9 (1.5 g, 2.94 mmol) was dissolved in of methanol (12 mL). Sodium methoxide (58 mg, 1.07 mmol, 0.37 eq) was added and the reaction was stirred over night. After completion, the solution was neutralized with Amberlite IR 120 (H+) ion exchange resin, filtered and concentrated in vacuo. The remainder was dried in high vacuum to give (2-Methyl-5-tert-butylphenyl) 1-thio-β-D-glucopyranoside S1 (1.0 g) which was used for the next reaction step without further purification. Tetrol S1 (1.0 g) was dissolved in anhydrous acetonitrile (11.3 mL) at RT under argon atmosphere and benzaldehyde dimethylacetal (880 μL, 5.84 mmol, 2 eq) and camphorsulfonic acid (7 mg, 0.029 mmol, 0.01 eq) were added. After 2.5 h (TLC: cyclohexane/ethyl acetate, 1:2), the reaction was quenched with triethylamine, and the solvents were evaporated in vacuo to give 1.5 g of colorless oil. The crude product was purified by column chromatography on silica gel (cyclohexane/ethyl acetate) to afford 10 (1.09 g, 2.53 mmol, 87%). [α]D20=−49.4° (c=1.0, CH2Cl2); IR (CH2Cl2): 3410, 2963, 2870, 1384, 1264, 1082, 1072, 1029, 1003, 972 cm−1; 1H-NMR (400 MHz, CDCl3) δ 7.61 (1H, d, J 2.0 Hz, Ar—H), 7.51-7.46 (2H, m, Ar—H), 7.39-7.35 (m, 3H, Ar—H), 7.29-7.23 (m, 2H, Ar—H), 7.16 (1H, d, J=8.0, Ar—H), 5.54 (1H, s, benzylidene-H), 4.64 (1H, d, J 10.0, 1-H), 4.36 (1H, dd, J1 10.3, J2 4.5, 6-Ha), 3.90-3.73 (2H, m, 3-H, 6-Hb), 3.59-3.47 (3H, m, 2-H, 4-H, 5-H), 2.86 (1H, d, J 2.2, OH), 2.69 (1H, d, J 2.4, OH), 2.42 (3H, s, CH3), 1.32 (9H, s, t-Bu); 13C-NMR (100 MHz, CDCl3) δ 149.7, 137.1, 137.0, 131.0, 130.3, 130.2, 129.4, 128.5, 126.4, 125.5 (C-aromatic), 102.0 (C-benzylidene), 88.8 (C-1), 80.4 (C-2), 74.8 (C-3), 73.0 (C-4), 70.5 (C-5), 68.7 (C-6), 31.4 (tBu), 20.6 (CH3); HRMS (ESI): Calcd for C24H30O5S [M+Na]+ 453.1706. found 453.1714.
