To a solution of 9-chloro-1-(2-chloro-4-methoxyphenyl)-6-[1-(ethenyloxy)propyl]-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole (170 mg, 0.39 mmol) in dichloromethane (4.0 mL) was added a solution of diethyl zinc in hexane (1.0 M, 2.0 mL, 2.0 mmol) and diiodomethane (0.31 mL, 3.84 mmol) at 0° C. After stirring at 0° C. for 1.5 hr, aqueous ammonium chloride was added to the reaction mixture at 0° C. The mixture was extracted with ethyl acetate. The organic layer was washed with water and brine, dried over anhydrous magnesium sulfate and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel eluting with a 10-50% ethyl acetate/n-hexane gradient mixture to give the title compound (87.7 mg, 0.196 mmol, 50%) as a pale yellow solid.
