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.
Light-induced dehydrogenation of 3,4-dihydropyrimidin-2(1H)-ones
作者:Hamid Reza Memarian、Asadollah Farhadi
DOI:10.1007/s00706-009-0156-0
日期:2009.10
UV light irradiation of Biginelli 3,4-dihydropyrimidin-2(1H)-ones in chloroform in an argon atmosphere leads to dehydrogenation of these compounds to their corresponding pyrimidin-2(1H)-ones in excellent yields. Irradiation in the same solvent under an oxygen atmosphere generates, in addition, various hitherto unidentified products. A light-induced electron transfer from the substrate to the solvent is proposed as the initial event, supported by the detection of dichloromethane and hydrogen chloride in the photolysate.