Ethylmagnesium bromide (3.0 M solution in diethyl ether, 3.19 mL, 9.57 mmol) was added to a stirred solution of 1-(2,4-dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole-6-carbonitrile (1.64 g, 4.78 mmol) in tetrahydrofuran (15 mL) at 0° C., and the mixture was stirred at 50° C. 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. Sodium borohydride (361 mg, 9.54 mmol) was added to a stirred solution of the resulting imine, and the mixture was stirred at room temperature for 2 hr. The reaction was quenched by aqueous saturated ammonium chloride 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. Formaldehyde (36-38% solution in water, 678 mg) was added to a solution of the resulting benzylamine (510 mg) in acetonitrile (4.0 mL). After 5 min sodium cyanoborohydride (510 mg, 8.14 mmol) was added to the mixture, and the mixture was stirred at room temperature for 3 hr. The mixture was diluted with saturated aqueous sodium hydrogen carbonate and 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 purified by flash column chromatography on silica gel eluting with a 5-50% ethyl acetate/n-hexane gradient mixture. The filtrate was concentrated in vacuo to give the solid, which was recrystallized from ethyl acetate/diisopropyl ether to give the title compound as a colorless crystal (100 mg, 0.248 mmol, 18% in 3 steps).
