A variety of Biginelli 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones are efficiently oxidized to their corresponding pyrimidin-2(1H)-one derivatives upon UV irradiation under argon atmosphere in chloroform solution. The nature of the additional substituent on the phenyl ring located on C-4 of the heterocyclic ring influences the rate of reaction. An electron-transfer induced photoreaction is proposed based
Free-radical oxidation of 4-substituted 5-acetyl- and 5-carboethoxy-1,2,3,4-tetrahydro-2-oxopyrimidines using benzoyl peroxide under thermal conditions has been investigated to elucidate the effects of the nature of the substituents in the 4- and 5-positions on the rate of reaction. Whereas the presence of the acetyl group instead of the carboethoxy group in position 5 decreases the rate of oxidation, the nature of the additional substituent (electron-releasing or electron-withdrawing group) and also its location on the phenyl ring attached to C-4 of the tetrahydropyrimidinone ring effectively influence the rate of reaction. The latter observation supports the proposal that the removal of the 4-hydrogen on the heterocyclic ring occurs in the rate-determining step.
Ultrasound-assisted dehydrogenation of 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones
In this study, various 5-acetyl-3,4-dihydropyrimidin-2(1H)-ones were synthesized and the dehydrogenation of these compounds by potassium peroxydisulfate in aqueous acetonitrile under thermal and sono-thermal conditions were investigated. Whereas the effect of the nature of 4-substituent influences the rate of reaction, the application of sonic waves decreases drastically the time of thermal reaction. (c) 2009 Elsevier B.V. All rights reserved.