Solvent-Free and Catalyst-Free Biginelli Reaction To Synthesize Ferrocenoyl Dihydropyrimidine and Kinetic Method To Express Radical-Scavenging Ability

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• 作者：Rui Wang ; Zai-Qun Liu
• 刊名：The Journal of Organic Chemistry
• 出版年：2012
• 出版时间：April 20, 2012
• 年：2012
• 卷：77
• 期：8
• 页码：3952-3958
• 全文大小：348K
• 年卷期：v.77,no.8(April 20, 2012)
• ISSN：1520-6904

文摘

Benzoyl and ferrocenoyl 3,4-dihydropyrimidin-2(1H)-ones (-thiones) (DHPMs) were synthesized in modest yields via catalyst-free and solvent-free Biginelli condensation of 1-phenylbutane-1,3-dione or 1-ferrocenylbutane-1,3-dione, hydroxyl benzaldehyde, and urea or thiourea. This synthetic protocol revealed that catalysts may not be necessary for the self-assembling Biginelli reaction. The radical-scavenging abilities of the obtained 11 DHPMs were carried out by reacting with 2,2鈥?azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS^{+鈥?/sup>), galvinoxyl radical, and 2,2鈥?diphenyl-1-picrylhydrazyl radical (DPPH), respectively. The variation of the concentration of these radicals with the reaction time (t) followed exponential function, [radical] = Ae鈥?i>t/a + Be鈥?i>t/b + C. Then, the differential style of this equation led to the relationship between the reaction rate (r) and the reaction time (t), 鈥?i>d[radical]/dt = (A/a)e鈥?i>t/a + (B/b)e鈥?i>t/b, which can be used to calculate the reaction rate at any time point. On the basis of the concept of the reaction rate, r = k[radical][antioxidant], the rate constant (k) can be calculated with the time point being t = 0. By the comparison of k of DHPMs, it can be concluded that phenolic ortho-dihydroxyl groups markedly enhanced the abilities of DHPMs to quench ABTS+鈥?/sup>, but the introduction of ferrocenoyl group made DHPMs efficient ABTS+鈥?/sup> scavengers even in the absence of phenolic hydroxyl group. This phenomenon was also found in DHPM-scavenging galvinoxyl radical. In contrast, the ferrocenoyl group cannot enhance the abilities of DHPMs to scavenge DPPH, and phenolic ortho-dihydroxyl groups still played the key role in this case.}