[CH3:1][N:2]1[C:6]2[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=2[N:4]=[C:3]1[CH:11]=O.[CH2:13]([O:15][CH:16]([O:19][CH2:20]C)[CH2:17][NH2:18])C.[BH3-]C#N.[Na+]>CO.C(O)(=O)C>[CH3:13][O:15][CH:16]([O:19][CH3:20])[CH2:17][NH:18][CH2:11][C:3]1[N:2]([CH3:1])[C:6]2[CH:7]=[CH:8][CH:9]=[CH:10][C:5]=2[N:4]=1
A solution of 1-methyl-2-formylbenzimidazole (1 g) in methanol (27 mL) and acetic acid (0.54 mL) was treated with aminoacetaldehyde diethylacetal (0.9 g, 1 equivalent) and NaCNBH3 (0.85 g, 2 equivalents) at 25° C., stirred for 1 hour. The mixture was partitioned between water and ethyl acetate. The organic layer was separated, washed sequentially with saturated NaHCO3 and brine, and concentrated. The residue was chromatographed on silica gel, eluting with 8% methanol/dichloromethane to give 1.2 g (64%) of the title compound.
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