[O:1]=[C:2]1[NH:6][C:5]2[CH:7]=[CH:8][CH:9]=[C:10]([C:11]([O:13]C)=O)[C:4]=2[NH:3]1.[CH2:15]([Mg]Br)[CH3:16].[CH2:19](OCC)[CH3:20].Cl>O1CCCC1.CO>[CH2:19]([C:11]([C:10]1[C:4]2[NH:3][C:2](=[O:1])[NH:6][C:5]=2[CH:7]=[CH:8][CH:9]=1)([OH:13])[CH2:15][CH3:16])[CH3:20]
To a suspension of methyl 2-oxo-2,3-dihydro-1H-benzimidazole-4-carboxylate (35.9 g, 189 mmol) in tetrahydrofuran (700 mL) was added dropwise 3M solution of ethylmagnesium bromide in diethyl ether (374 mL, 1.12 mol), and the mixture was refluxed for 3 hr. After cooling, methanol (70 mL) was added dropwise at 0° C., and 1 N hydrochloric acid (1300 mL) was added at 0° C. The mixture was stirred at room temperature for 40 min, and the organic layer was seated and concentrated in vacuo. The aqueous layer was extracted with ethyl acetate (400 mL×2). The combined organic layer was concentrated in vacuo. The resulting solid was suspended in diisopropyl ether (70 mL)-water (10 mL)-ethyl acetate (40 mL), and the mixture was refluxed for 30 min. After cooling to room temperature, the resulting solid was collected by filtration and washed with diisopropyl ether to give the title compound (33.0 g, 150 mmol, 79%) as a pale yellow solid.
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