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A variety of 4-substituted 5-acetyl-and 5-carboethoxy-2-oxo-1,2,3,4-tetrahydropyrimidines were oxidized under UV irradiation in the presence or absence of benzoyl peroxide. The nature of the substituents on the 4-and 5-positions of the heterocyclic ring affects the rate of photo-oxidation, and irradiation of these compounds in the presence of benzoyl peroxide decreases the time of reaction drastically. Removal of 4-H by a benzoyloxy radical under formation of a trihydropyrimidinoyl radical intermediate occurs in the rate-determining step. The stability of this benzylic and allylic radical intermediate is affected by the nature and the position of the additional substituent on the phenyl group located at C-4.

Light-Induced Free Radical Oxidation of 2-Oxo-1,2,3,4-tetrahydropyrimidines. -The dehydrogenation of title tetrahydropyrimidinones (I) and (III) proceeds smoothly by UV-irradiation in the presence of benzoyl peroxide under argon atmosphere. Excellent regioselectivity is achieved providing 1,2-dihydropyrimidin-2-ones (II) and (IV), exclusively. -(MEMARIAN*, H. R.; HEJAZI, L.; FARHADI, A.; Z.

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