[C:1]([O:5][CH3:6])(=O)[CH:2]=[CH2:3].[NH2:7][C:8]1[NH:9][C:10]2[CH:16]=[C:15]([O:17][CH3:18])[C:14]([O:19]C)=[CH:13][C:11]=2[N:12]=1>CO>[CH3:6][O:5][C:1]1[C:15]([O:17][CH3:18])=[CH:16][C:10]2[N:9]=[C:8]3[NH:7][C:14](=[O:19])[CH2:13][CH2:11][N:12]3[C:3]=2[CH:2]=1Methyl acrylate (6.1 g.) was added to a solution of 2-amino-5,6-dimethoxybenzimidazole (12.2 g.) in methanol (70 ml.) and the mixture was stirred for 90 hours. The crystalline precipitate was separated by filtration and washed with ethanol and then ether to give 7,8-dimethoxy-3,4-dihydropyrimido[1,2-a]-benzimidazol-2(1H)-one (10.3 g.), m.p. 264°-5° C.; microanalysis, C12H13N3O3 requires: C, 58.3; H, 5.3; N, 17.0%; found: C, 58.0; H, 5.2; N, 16.8%; NMR: δ2.82 (t, 2 protons, C3-H2); 3.72 (s, 3 protons, CH3O); 3.76 (s, 3 protons, CH3O); 4.15 (t, protons C4 -H2); 7.00 (s, 1 proton, C6-H); 7.04 (s, 1 proton, C9-H).
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