反应详情

2-Bromo-5,6-dichlorobenzimidazole (0.25 g, 0.94 mmol), N,O-bis(trimethylsiyl) acetamide (Aldrich, 1.4 ml, 5.6 mmol), and acetonitrile (Aldrich Sure Seal, 20 ml) were combined and magnetically stirred under a nitrogen atmosphere for 1.5 h. To the silylated base was added 0.30 g (0.94 mmol) 1,2,3,4-tetra-O-acetyl-xylopyranose (Aldrich, Milwaukee) followed by stannic chloride (1.4 mmol, 0.12 ml, Aldrich, Milwaukee). The solution stirred under nitrogen overnight, and additional stannic chloride (0.35 ml, 4.1 mmol) was added the following day. One hour after the second addition of stannic chloride, the reaction was poured into saturated aqueous sodium sulfate, and filtered through a celite pad which was washed with chloroform and water. The filtrate layers were separated. The chloroform layer was washed with 2×150 ml saturated aq. sodium bicarbonate then with 1×150 ml of water. The organic layer was dried with magnesium sulfate (anhyd), filtered, and evaporated. The crude residue was purified on a silica gel column (2.5×20 cm, 230-400 mesh) with hexanes and a step gradient from 0 to 25% ethyl acetate to give the product, 2-bromo-5,6-dichloro-1-(2,3,4-tri-O-acetyl-beta-D-xylopyranosyl)-1H-benzimidazole (0.13 g, 0.24 mmol, 26%); 1H NMR (DMSO-d6) δ8.47-8.42 (bs,1H), 7.91 (s, 1H), 6.07-6.02 (bs, 1H), 5.66-5.54 (bs, 3H), 4.18-4.13 (m, 1H), 3.95-3.89 (m, 2H), 2.02 (s, 3H), 1.99 (s, 3H), 1.77 (bs, 3H).

1. stirringThe solution stirred under nitrogen overnight
2. filtrationfiltered through a celite pad which
3. washwas washed with chloroform and water
4. customThe filtrate layers were separated
5. washThe chloroform layer was washed with 2×150 ml saturated aq. sodium bicarbonate
6. dry with materialThe organic layer was dried with magnesium sulfate (anhyd)
7. filtrationfiltered
8. customevaporated
9. customThe crude residue was purified on a silica gel column (2.5×20 cm, 230-400 mesh) with hexanes