The semiconductor-sensitized oxidation of various 1-, 4- and 5-substituted 2-oxo-1,2,3,4-tetrahydropyrimidines was carried out in acetonitrile using TiO2 anatase nanoparticles. The aims of this study were to elucidate the effects of the nature of the substituents on the 1-, 4- and 5-positions of the heterocyclic ring, the type of the photocatalyst and the nature of solvent on the rate of reaction. The proposed electron-transfer mechanism is supported by the experimental results and also by the computational studies. (C) 2012 Elsevier B.V. All rights reserved.