2-Bromoethanol → 2-Bromoethyl 2,3,4,6-tetra-O-benzyl-alpha-D-galactopyranoside

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Reaction Steps

Trimethylsilyl bromide (7.96 g, 6.78 ml. 52 mmol) was added with a syringe to a mixture of 2,3,4,6-tetra-O-benzyl-D-galactopyranose (28 g, 52 mmol), 2-bromoethanol (4.46 ml, 40.0 mmol), cobalt(II)bromide (11.4 g, 52.0 mmol), tetraethylammonium bromide (10.9 g, 52.0 mmol) and molecular sieves (4 Å, 41 g) in 138 ml of methylene chloride under nitrogen with protection from light. (The cobalt(II)chloride had been dried at 180°, 5×10-3 mm Hg over night. ) The reaction mixture was stirred at room temperature over night and filtered. The residue was washed with 100 ml of methylene chloride. The filtrate was evaporated at reduced pressure to give 25.8 g of the crude product, which was chromatographed (SiO2, isooctane:ethyl acetate 3:2) Fraction 1 was the pure title compound (6.0 g) and fraction 2 was a mixture of the anomers (α/β, 10.0 g) Total yield of glycosides 16 g (48 %) (This procedure is a slight modification of that of Koto et al.34.) [α]D23 =+30.5° (c 1.4, CHCl3). 1H-NMR (CDCl3, TMS) δ 7.30 (m, 20H, Ph), 4.97-4.42 (m, 9H), 4.0-3.8 (m, 6H), 3.52 (t, 4H, inter alia CH2Br). 13C-NMR (CDCl, TMS) δ 103.3 (d, Cl, JC--H =168 Hz), 84.2, 81.6, 80.2, 75.0 (C2-C5), 80.0, 78.7, 78.6, 78.5, 74.2, 73.5 (C6, benzylic CH2 and aglycon O--CH2), 35.5 (CH2Br)

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