[C:1]([CH2:13][C:14]([O:16]CC)=O)(=O)[C:2]1[CH:11]=[CH:10][C:7]([O:8][CH3:9])=[C:4]([O:5][CH3:6])[CH:3]=1.[CH3:19][NH:20][C:21]([NH:23][CH3:24])=[O:22].C(O)C>Cl.O>[CH3:6][O:5][C:4]1[CH:3]=[C:2]([C:1]2[N:23]([CH3:24])[C:21](=[O:22])[N:20]([CH3:19])[C:14](=[O:16])[CH:13]=2)[CH:11]=[CH:10][C:7]=1[O:8][CH3:9]
To a mixture of ethyl veratroylacetate (10 g) and N,N'-dimethylurea (3.84 g) were added conc. hydrochloric acid (1 drop) and ethanol (1 ml). The mixture was heated at 120° C. for 3.5 hours under reduced pressure. To the residue was added another conc. hydrochloric acid (2 drops) and the mixture was heated again at 120° C. for 4 hours under reduced pressure. To the reaction mixture was added water and extracted with ethyl acetate. The extract was dried over magnesium sulfate and evaporated under reduced pressure. The residue was triturated with a mixture of isopropyl ether and ethyl acetate to give 6-(3,4-dimethoxyphenyl)-1,3-dimethyl-2,4(1H,3H)pyrimidinedione (7.60 g).
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