[N+:1]([C:4]1[CH:9]=[CH:8][C:7]([NH:10][C:11]2[NH:15][C:14]3[CH:16]=[CH:17][CH:18]=[CH:19][C:13]=3[N:12]=2)=[CH:6][CH:5]=1)([O-:3])=[O:2].[H-].[Na+].Br[CH2:23][CH2:24]Br>CN(C=O)C>[N+:1]([C:4]1[CH:5]=[CH:6][C:7]([N:10]2[C:11]3=[N:12][C:13]4[CH:19]=[CH:18][CH:17]=[CH:16][C:14]=4[N:15]3[CH2:24][CH2:23]2)=[CH:8][CH:9]=1)([O-:3])=[O:2]A mixture of N-(4-nitrophenyl)-1H-benzimidazol-2-amine (1.00 g) in DMF (20 mL) at ambient temperature was treated with a 60% dispersion of sodium hydride in mineral oil (393 mg) then stirred for 5 min. The mixture was treated with a solution of 1,2-dibromoethane (738 mg) in DMF (1 mL) then stirred at ambient temperature for 1 h. After this time, the reaction mixture was quenched with saturated aqueous ammonium chloride (10 mL), diluted with water (80 mL) and extracted with ethyl acetate (2×100 mL). The combined organic layers were washed with 5% aqueous lithium chloride (2×50 mL) then brine (50 mL), dried over sodium sulfate, and filtered and the filtrate was concentrated under reduced pressure. The residue obtained was purified by chromatography (silica, heptane to 1:1 ethyl acetate/heptane) to afford 1-(4-nitrophenyl)-2,3-dihydro-1H-imidazo[1,2-a]benzimidazole (63 mg) as a yellow solid.
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