A solution of 9-chloro-1-(2,4-dichlorophenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-6-amine (367 mg, 1.00 mmol), (1-ethoxycyclopropoxy)trimethylsilane (1.01 mL, 5.00 mmol), sodium cyanoborohydride (314 mg, 5.00 mmol), and acetic acid (572 μL, 10.0 mmol) in methanol (3.0 mL) was stirred at reflux for 40 h. The reaction mixture was diluted with ethyl acetate, quenched with aqueous sodium hydrogen carbonate, and filtrated. The organic layer was washed with brine, dried over sodium sulfate, filtered, and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel eluting with a 20% ethyl acetate/hexane mixture to give the title compound as a colorless solid (83.5 mg, 0.186 mmol, 19%). Analytically pure material was obtained by recrystallization from ethyl acetate/hexane.
