2-Nitro-1H-benzimidazole → 1-Propyl-1H-benzoimidazol-5-ylamine

A solution of 5-nitrobenzimidazole (3.6 g, 23 mmol) in 100 ml of THF was stirred with NaH (1.5 g, 33 mmol) for 0.5 h at 25° C. To the solution was added allyl bromide (4.8 ml, 57 mmol) and resulting mixture was stirred for 12 h. The reaction mixture was concentrated in vacuo to provide an oil, which was subjected to column chromatography to yield 4.0 g (19.7 mmol, 89%) of a mixture of 1- and 3-allyl-5-nitrobenzimidazole. The nitrobenzimidazole mixture was stirred in 100 ml of MeOH for 12 under H2 in the presence of 10% Pd/C. The reaction mixture was filtered and concentrated in vacuo to provide oily residue which was subjected to column chromatography (50% Hexane/EtOAc) to provide 1.2 g (7.0 mmol) of 1-propyl-5-aminobenzimidazole and 1.1 9 (6.4 mmol) of 3-propyl-5-aminobenzimidazole.