Reaction Steps
Hydrogen bromide (2 mL of a 30% solution in acetic acid) was added to a solution of 6-azido-6-deoxy-1,2,3,4-tetra-O-acetyl-galactopyranose 36 (α:β, 0.8:1) (320 mg, 0.86 mmol) in anhydrous DCM (10 mL). The mixture was stirred under argon at 0° C. After 1¾h, t.1.c. (petrol:ethyl acetate, 2:1) indicated the formation of two products (Rf 0.5, 0.2) with some remaining starting material (Rf 0.3). The reaction mixture was quenched with ice/water (30 mL), diluted with DCM (40 mL), neutralized with sodium bicarbonate (2×40 mL), washed with brine (40 mL), dried (MgSO4), filtered and concentrated in vacuo to yield 350 mg of crude product, which was used without further purification, but a small portion was retained and purified by flash column chromatography (DCM:ether, 60:1) to afford 2,3,4-tri-O-acetyl-6-azido-6-deoxy-α-D-galactopyranosylbromide 37 as a white solid Rf 0.5 (60:1, DCM:ether); m.p. 81.5-82.2C (ether/petrol) [Lit. 82-83° C. (ether/petrol) Jezo, I. and Zemek, J., Chemicke Zvesti, 33, 533-541 (1979)]; [α]D25+70.8 (c, 1.7 in CHCl3) [Lit. [α]D22 +133.8 (c, 1 in CHCl3)], νmax (thin film) 2107 (sh, N3), 1750 (st, C═O)cm−1; δH (400 MHz, CDCl3) 2.03, 2.12, 2,18 (9H, 3 x s, 3 x CH3), 3.30-3.40 (2H, m, H-6, H-6′), 4.47 (1H, t, H-5), 5.04 (1H, dd, J1,2 4.0, J2,3 10.7, H-2), 5.43 (1H, dd, J3,4 3.2, H-3), 5.69 (1H, m, H-4), 6.69 (1H, d, H-1).
