Ethylmagnesium bromide (3 M solution in diethyl ether, 4.50 mL, 13.5 mmol) was added to a stirred suspension of 9-chloro-1-(2,4-dichloro-6-methylphenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole-6-carbonitrile (530 mg, 1.35 mmol) in tetrahydrofuran (14 mL) at room temperature. After the resultant mixture was refluxed for 3 hr, a suspension of sodium tetrahydroborate (1.02 g, 27.0 mmol) in 2-propanol (14 mL) was added at room temperature. The resultant mixture was stirred at 50° C. for 30 min, diluted with water, and extracted with ethyl acetate. The combined organic layer was washed with brine, dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo to give crude 1-[9-chloro-1-(2,4-dichloro-6-methylphenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-6-yl]propan-1-amine (609 mg), which was used for the next step without further purification. To a mixture of crude 1-[9-chloro-1-(2,4-dichloro-6-methylphenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-6-yl]propan-1-amine (120 mg) and triethylamine (0.0742 mL, 0.532 mmol) in tetrahydrofuran (2.7 mL) was added acetic anhydride (0.0302 mL, 0.319 mol) at 0° C. The resultant mixture was stirred at room temperature for 10 min, diluted with aqueous sodium bicarbonate and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel eluting with a 20-100% ethyl acetate/n-hexane gradient mixture and preparative HPLC eluting with a 10-40% acetonitrile/water gradient mixture to give the two title compounds as colorless solids.
