[CH3:1][NH:2][C:3]([NH:5][CH:6]1[CH2:11][CH2:10][CH2:9][CH2:8][CH2:7]1)=[O:4].[C:12](O)(=[O:17])[CH2:13][C:14](O)=[O:15].C(OC(=O)C)(=O)C.O>C(O)(=O)C.CO>[CH3:1][N:2]1[C:12](=[O:17])[CH2:13][C:14](=[O:15])[N:5]([CH:6]2[CH2:11][CH2:10][CH2:9][CH2:8][CH2:7]2)[C:3]1=[O:4]In 15 ml of acetic acid is dissolved 5 g of N-methyl-N'-cyclohexylurea together with 5 g of malonic acid under heating. Then, at 70° C., 15 ml of acetic anhydride is added dropwise over a period of 30 minutes. The mixture is further heated at 80°-90° C. for 2 hours, after which time 5 ml of water is added. The mixture is heated at 70° C. for 30 minutes and, then, concentrated to dryness. By the above procedure is obtained a pale-yellow oil. This oil is dissolved in methanol and allowed to stand in a refrigerator, whereupon needles separate out. These crystals are collected by filtration and washed with ethanol. The above procedure provided 6.9 g of 1-methyl-3-cyclohexylbarbituric acid as colorless crystals, melting point: 81°-82° C.
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