Tetrahydrofuran → 1-[1-(2,4-Dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-6-yl]propan-1-one

Ethylmagnesium bromide (3.0 M solution in diethyl ether, 14.6 mL, 43.7 mmol) was added to a stirred solution of 1-(2,4-dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole-6-carbonitrile (5.00 g, 14.6 mmol) in tetrahydrofuran (50 mL) at 0° C., and the mixture was stirred at 50° C. for 2 hr. The reaction was quenched by methanol, and the mixture was diluted with aqueous saturated ammonium chloride and extracted with ethyl acetate. The combined organic layer was washed with brine, dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo. A mixture of the resulting imine, acetic acid (10 mL) and 1N hydrochloric acid (20 mL) was stirred at 50° C. for 2 hr. The mixture was concentrated in vacuo, 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 recrystallized from ethyl acetate/diisopropyl ether to give the title compounds as a colorless crystal (3.04 g, 8.12 mmol, 56%).