[Synthesis]
GENERAL STEPS: 2-Aminobenzimidazole (3.9 g, 22.5 mmol) was dissolved in a solvent mixture of tetrahydrofuran (THF, 30 mL) and ethanol (EtOH, 15 mL) in a sealed reaction flask. Subsequently, finely ground potassium hydroxide (KOH, 1.52 g, 27.0 mmol) was added and stirred for 20 min at room temperature. Next, bromopropane (2.77 g, 22.53 mmol) was slowly added to the reaction system. The reaction mixture was heated to 65 °C and stirred continuously for 72 hours. After completion of the reaction, it was cooled to room temperature and filtered to remove insoluble material. The filtrate was concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography with the eluent being a mixed solvent of 1% ammonia (NH4OH)/9% methanol (MeOH)/90% chloroform (CHCl3), which resulted in 1-propyl-1H-benzo[d]imidazol-2-amine as a yellow solid (2.5 g, 63% yield). The product was detected by LC-MS (ES), m/z = 176.0 ([M + H]+). 1H NMR (400 MHz, DMSO-d6) δ 7.14 (s, 1H), 7.10 (d, J = 8.0 Hz, 1H), 6.86-6.92 (m, 2H), 6.38 (s, 2H), 3.90 (t, J = 6.9 Hz, 2H) , 1.62-1.68 (m, 2H), 0.84 (t, J = 7.3 Hz, 3H). |