A new convenient method for the preparation of heterocyclic bis-adducts of 5(6)-substituted uraciles with ftorotan with 18-crown-6-complex as catalyst was described. The structure of synthesized compounds has been confirmed by data of elemental analysis, UV-, IR- and NMRІН-spectra. The purity has been tested by method of thin-layer and gas-liquid chromatography. It was discovered that compounds, which synthesized apply to little toxic preparations: LD50 are from 515 to 125 mg/kg. A strongly antitumour effect of bis-adduct of 5-fluorouracile has been discovered: growth relaxation of Plissa Lymphosarcoma tumour mass was 75.3%.
