Reaction Steps
2,3,4-tri-O-acetyl-6-azido-6-deoxy-α-D-galactopyranosylbromide 37 (100 mg, 0.25 mmol) and p-nitrophenol (37 mg, 0.27 mmol) were dissolved in DCM. This solution was added to a stirred suspension of 2,6-di-tert-butyl-4-methyl-pyridine (37 mg, 0.18 mmol), silver triflate (87 mg, 0.30 mmol) and molecular sieves (3 Å) in DCM (7 ml). The reaction mixture was stirred under argon. After 1 h, t.1.c. (petrol:ethyl acetate, 2:1) indicated complete consumption of starting material (Rf 0.4). The reaction mixture was filtered through celite, concentrated in vacuo and co-evaporated with water. The residue was purified by flash column chromatography (DCM:ether, 30:1) to afford 1,3,4-tri-O-acetyl-6-azido-6-deoxy-2-hydroxy-α-b-galactopyranose 39 (55 mg, 65%) as a colourless oil (Rf 0.5); partial data [α]D25 +68.7 (c, 0.2 in CHCl3); νmax (thin film) 3432 (br, OH), 2101 (sh, N3) 1644 (st, C═O)cm−1; δH (400 MHz, CDCl3) 2.02, 2.03, 2.17, 2.18 (12H, 4 x s, 4 x CH3), 3.28 (11H, dd, J5,6 7.8 Hz, J6,6′ 10.3Hz, H-6), 3.35 (1H, dd, J5,6′ 6.2 Hz, H-6′), 4.31 (1H, m, H-5), 5.32 (1H, dd, J2,3 3.2 Hz, J2,3 11.0 Hz, H-2), 5.37 (1H, dd, J3,4 3.1 Hz, H-3), 5.69-5.70 (1H, m, H-4), 6.37 (1H, d, H-1); δC (100.6 MHz, CDCl3) 20.5, 20.6, 20.9 (3 x q, 3 x CH3), 27.4 (t, C-6), 66.2 (d, C-2), 67.5 (d, C-3), 67.7 (d, C-4), 71.2 (d, C-5), 89.6 (d, C-1), 168.9, 169.9, 170.1 (3 x s, 3 x C═O).
