Capto-Dative Stabilization by Thermal Oxidation of 2-Oxo-1,2,3,4-tetrahydropyrimidines

摘要

Various 4,6-diaryl substituted 2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs) were oxidized to 2-oxo-1,2-dihydropyrimidines (DHPMs) by potassium peroxydisulfate (PPS) in aqueous acetonitrile solution under thermal conditions. Based on the proposed oxidation reaction mechanism by way of a radical, a capto-dative stabilized radical intermediate, among two possible formed double benzylic/allylic radical centres, governs the type of product formed. Whereas the electron-donating nature of the additional methoxy-substituent enhances the rate of oxidation, its attachment to the radical intermediate decreases the radical stability, simultaneously causing the shift of the radical centre to the capto-dative stabilized benzylic radical centre. The data of the density functional theory computational studies concerning the bond lengths to the radical centres and Mulliken population analysis support the results of the experimental work.