[Cl:1][C:2]1[C:10]2[N:9]=[C:8]3[N:11]([C:15]4[CH:20]=[CH:19][C:18]([O:21][CH3:22])=[CH:17][C:16]=4[Cl:23])[CH2:12][CH2:13][CH2:14][N:7]3[C:6]=2[C:5]([CH:24]([OH:27])[CH2:25][CH3:26])=[CH:4][CH:3]=1.[C:28](OC(=O)C)(=[O:30])[CH3:29]>N1C=CC=CC=1>[C:28]([O:27][CH:24]([C:5]1[C:6]2[N:7]3[CH2:14][CH2:13][CH2:12][N:11]([C:15]4[CH:20]=[CH:19][C:18]([O:21][CH3:22])=[CH:17][C:16]=4[Cl:23])[C:8]3=[N:9][C:10]=2[C:2]([Cl:1])=[CH:3][CH:4]=1)[CH2:25][CH3:26])(=[O:30])[CH3:29]To a solution of 1-[9-chloro-1-(2-chloro-4-methoxyphenyl)-1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazol-6-yl]propan-1-ol (122.0 mg, 0.300 mmol) in pyridine (0.5 mL) was added acetic anhydride (0.5 mL) at 0° C. The reaction mixture was stirred at room temperature for 5 hrs. The mixture was concentrated. The residue was neutralized with aqueous saturated sodium hydrogen carbonate and extracted with ethyl acetate (×3). The combined organic layer was washed with brine (×1), dried over anhydrous magnesium sulfate, filtered and concentrated in vacuo. The residue was purified by silica gel column chromatography eluting with a 0-40% ethyl acetate/n-hexane gradient mixture. The residue was recrystallized from methanol/n-hexane to give the title compound as a colorless powder (94.7 mg, 0.211 mmol, 70%).
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