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In recent years hydantoins (4-oxoimidazolidin-2-ones) and 2-thiohydantoins (4-oxoimidazolidine-2-thiones) have been actively investigated in connection with the wide spectrum of their biological activity. Apart from this hydantoins and thiohydantoins are precursors in the synthesis of a wide range of organic compounds, for example, amino acids [1][2][3][4][5].We have shown previously that 3-methyl-5-benzylidenethiohydantoin reacts with bromine in acetic acid, adding Br 2 at the C=C double bond, with further substitution of one of the bromine atoms by an ethoxy group on reaction with ethanol [6,7].In this work the possibility of obtaining 5-bromo(aryl)methylene-substituted hydantoins by the bromination of 2-aryl-and hetarylmethylene-substituted 2-thiohydantoins has been demonstrated. The 5-aryl-3,5-dihydro-4H-2-methylthioimidazol-4-ones were obtained by a previously described method [8]. Bromination of S-alkylated derivatives of 2-thiohydantoin were carried out by slow addition of a solution of 1.1 equiv of bromine in CH 2 Cl 2 to a solution of compound 1 or 2 in the same solvent. From the bromination of 2-methylthio-5-(phenylmethylene)-3-phenyl-3,5-dihydro-4H-imidazol-4-one we isolated the product of the addition of bromine to the double bond of the 2-thiohydantoin 3, which degraded on standing. In the case of the S-alkylated derivative of 2-thiohydantoin containing a pyridomethylene substituent at position 5, a complex of 2-methylthio-5-(2-pyridylmethylene)-3.5-dihydro-4H-imidazol-4-one with bromine 4 was formed. In the 1 H NMR spectrum signals of aromatic systems of this compound are shifted to the weak-field region. Boiling both compounds 3 and 4 in ethanol gave compounds 5 and 6, containing a bromoarylmethylene unit. _______ * Dedicated to Academician B. A. Trofimov on his 70 th jubilee. __________________________________________________________________________________________

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