Photo-dehydrogenation of 4,6-diaryl-2-oxo-1,2,3,4-tetrahydropyrimidines

Abstract

Electron-transfer-induced photo-oxidation of 4,6-diaryl-substituted 2-oxo-1,2,3,4-tetrahydropyrimidines (THPMs) in chloroform under argon atmosphere results in the smooth formation of 4,6-diaryl-substituted 2-oxo-1,2-dihydropyrimidines. Sequentially, electron-transfer and proton removal processes in this oxidative reaction result in the occurrence of two different benzylic and allylic radical intermediates, which converted to each other via resonance. Preferably, capto-dative stabilized radical center stimulates the type of product. Based on the proposed oxidation reaction mechanism, the electron transfer from the excited THPMs to chloroform starts this oxidative reaction. The results of the computational study obtained at DFT-B3LYP/6-311++G** level of theory indicate that the first electron is preferably removed from the N1 atom of the heterocyclic ring. A comparison of the sum of the Mulliken spin densities of the radical intermediates supports the argument that the more stable capto-dative stabilized radical is involved in the reaction.