Tetrabutylammonium fluoride (1.0 M solution in tetrahydrofuran, 1.1 mL, 1.1 mmol) was added dropwise to a stirred solution of 9-chloro-1-(2-methoxy-4,6-dimethylpyrimidin-5-yl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazole-6-carbaldehyde (4.12 g, 11.1 mmol) and trimethyl(trifluoromethyl)silane (3.16 g, 22.2 mmol) in tetrahydrofuran (45 mL) at 0° C., and the mixture was stirred at 0° C. for 20 min. 1N hydrochloric acid (35 mL) was added to the mixture at 0° C., and the mixture was stirred at 0° C. for 30 min. The mixture was neutralized 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 75-100% ethyl acetate/n-hexane gradient mixture. The filtrate was concentrated in vacuo to give the solid, which was washed with ethyl acetate/diisopropyl ether to give the title compound as a colorless powder (3.96, 8.96 mmol, 81%).
