Trimethylsilyl triflate → 2-Chloro-5,6-dibromo-1-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)benzimidazole

Participants

Reaction Steps

A suspension of 931 mg (3 mmole) of 2-chloro-5,6-dibromobenzimidazole (17) in 15 ml of dry CH3CN was treated with 0.8 mL (3 mmole) of N,O-bis(trimethylsilyl) trifluoroacetamide (BSTFA) at 75° C. for 10 min to give a clear solution. To this solution, was added 955 mg (3 mmole) of 1,2,3,5-tetra-O-acetyl-β-D-ribofuranose and 0 64 mL (3.3 mmole) of trimethylsilyl triflate (TMSTf). Stirring was continued at 75° C. for 1 hr. The reaction mixture was cooled to room temperature and then diluted with 100 mL of EtOAc. The EtOAc solution was washed with a sat. NaHCO3 solution (100 mL×2), sat. NaCl solution (100 mL), dried (Na2SO4), and evaporated. The residue was chromatographed on a silica column (3×20 cm, eluted with CHCl3). Evaporation of fractions 4-10 and recrystallization of the residue from MeOH gave 946 mg (56%) of 56 as white crystals. mp 140°-142° C.; MS m/e 565.9082 (0.9%, M+ =565.9091); 1H NMR (DMSO-d6) d 8.20 (s, 1,7-H), 8.11 (s, 1, 4-H), 6.25 (d, 1, 1'-H), 5.55 (t, 1, 2'-H), 5.43 (dd, 1, 3'-H), 4.47 (m, 2, 5'-H, 4'-H), 4.37 (m, 1, 5"-H), 2.15, 2.14, 2.02 (3×s, 3×, 3.3×Ac). Evaporation of fractions 13-15 gave 392 mg (23%) of the a anomer as a white foam. 1H NMR (DMSO-6) d 8.07, 8.06 (2×s, 2, 4-H, 7-H), 6.70 (d, 1, 1'-H), 5.71 (t, 1, 2'-H), 5.50 (dd, 1, 3 '-H), 4.81 (m. 1, 4'-H), 4. 36 (dd, 1, 5'-H), 427 (dd, 1, 5"-H).

Provenance & Evidence