9-Chloro-1-(2,4-dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole-6-carbaldehyde → 1-[9-Chloro-1-(2,4-dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-6-yl]butan-1-ol

n-Propylmagnesium bromide (2.0 M solution in tetrahydrofuran, 0.72 mL, 1.44 mmol) was added to a stirred solution of 9-chloro-1-(2,4-dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole-6-carbaldehyde (500 mg, 1.31 mmol) in tetrahydrofuran (3.0 mL) at 0° C., and the mixture was stirred at room temperature for 2 hr. The reaction was quenched by water, and the mixture was extracted with ethyl acetate. The combined organic layer was washed with brine, dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo. The residue was recrystallized from ethanol to give the title compound as a colorless crystal (435 mg, 1.02 mmol, 78%).