Reaction Steps
Compound 10b (0.56 g) was dissolved in a mixture of benzene (30 mL) and triethylorthoacetate (30 mL), containing 4-toluenesulfonic acid (0.15 g), and the mixture stirred for 1 h at room temperature. The acid was neutralized with a little triethylamine, and the mixture evaporated to dryness. It was then taken in 80% aqueous acetic acid (50 mL) and stirred for 40 min at room temperature. T.l.c. (4:1 toluene-ethyl acetate) showed the presence of a major product,faster-migrating than diol 10b. The acetic acid was removed under diminished pressure, and several portion of toluene were added to, and evaporated from the residue to furnish 11b (0.56 g, 96.6%) as an amorphous solid, [α]D -14.3° (c,1.1, chloroform). 1H NMR (CDCl3): δ8.20-7.00 (m, 40 H, arom.), 5.51 (t, 1 H, J 8.0 Hz, H-2'), 5.38 (d, 1 H, J 3.8 Hz, H-1 fuc), 5.30 (d, 1 H, J 3.8 Hz, H-4'), 5.20 (dd, 1 H, J 8.1 and 10.0 Hz, H-2), 4.62 (d, 1 H, J 8.2 Hz, H-1), 4.44 (d, 1 H, J 7.9 Hz, H-1'), 1.82 (s, 3 H, CH3CO), and 1.34 (d, 3 H, J 6.4 Hz, H-6 fuc). 13C NMR (CDCl3): δ170.38 (CH3CO), 166.15, 165.72, 165.57, 164.56 (4×PhCO), 100.45, 99.23 (C-1, C-1'), 97.54 C-1 fuc), 79.48 (C-3), 77.57 (C-4), 74.08, 72.94, 72.70, 70.15 (4×PhCH2), 62.54, 60.78 (C-6, C-6'), 20.59 (CH3CO), and 16.88 (C-6 fuc); positive ion LSIMS: 1307.1 (M+H)+), 1200.8 (M-OBn)+, negative ion LSIMS: 1460.9 (M+mNBA)-, 1353.6 (M+NO2)-, 1306.8 (M-H)-.
