H. Memarian, Esmael Sanchooli
Feb 1, 2016
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0
Influential Citations
7
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Journal
Magnetic Resonance in Chemistry
Abstract
Tetrahydropyrimidinone (THPMs) derivatives previously known as 3,4-dihydropyimidine-2-(1H)-ones (DHPMs) exhibit a wide range of biological activities and pharmaceutical properties. Therefore, because of their importance various works are devoted to the synthesis of these nitrogen containing heterocyclic compounds. In our previous studies, we were interested in elucidating the parameters affecting the rate of thermal and photochemical oxidation of some nitrogen containing heterocyclic compounds, e.g. 1,4-dihydropyridines (DHPs), 2-oxo-1,2,3,4tetrahydropyrimidines (THPMs) and 2,3-dihydroquinazolinones (DHQZs). The results of experimental work concerning the steric and electronic effects of the substituent on the light-induced oxidation, thermal oxidation and also computational studies in the THPM system indicate that the electronic nature and steric effect of the additional substituent, on the aryl ring attached to the C4-atom, influence the electron density of the heterocyclic ring through the σ bond, while the same effects are observed via conjugation of the C5-substituent with the C51⁄4C6 double bond (Scheme 1). Consequently, the oxidative behavior of 5-substituted THPMs depends on the steric and electronic effects of the substituents on the 4and 5-positions of the heterocyclic ring. Recently, we have investigated the electronic effect of 4-substitution on the tautomerism in 5-acetyl-2-methoxydihydropyrimidines based on the NMR and computational DFT studies. In continuation to these studies, we were interested in investigating these effects in 4,6-diaryl-2-oxo-1,2,3,4-tetrahydropyrimidines (1a–g), containing a methoxy group on the different positions of either 4or 6-aryl rings, especially on the chemical shifts of some characteristic NMR peaks. For better observation of these effects by the aryl substitution via σor π-interaction, especially the steric effect, the heterocyclic ring does not contain any substituent on the 5-position (Scheme 2).