Step A: Synthesis of 5-bromo-1H-benzimidazol-2-amine
[00400] 4-Bromo-1,2-benzenediamine (4 g, 21.39 mmol) was dissolved in methanol (20 mL) to form a dark brown solution. Cyanogen bromide (2.492 g, 23.52 mmol) was added to this solution. The reaction was exothermic and the methanol began to boil after a few seconds. After 5 minutes of reaction, the reaction mixture was diluted with ethyl acetate (100 mL) and washed sequentially with saturated aqueous sodium bicarbonate solution (100 mL) and saturated sodium chloride solution (100 mL). After concentrating the organic layer to a few mL, it was purified by silica gel column chromatography (0-20% methanol/ethyl acetate gradient elution) to afford 5-bromo-1H-benzimidazol-2-amine (3.9 g, 18.39 mmol, 86% yield) as a black solid.
1H NMR (400 MHz, DMSO-d6) δ ppm: 6.47 (br.s., 2H), 6.94-7.00 (m, 1H), 7.01-7.06 (m, 1H), 7.23 (d, J = 1.85 Hz, 1H), 8.70-11.33 (m, 1H); ES LC-MS m/z = 212.2 (Br 79, M + H)+, ES LC-MS m/z = 214.2 (Br 81, M + H)+.
