Structural and Medium Effects on the Reactions of the Cumyloxyl Radical with Intramolecular Hydrogen Bonded Phenols. The Interplay Between Hydrogen-Bonding and Acid-Base Interactions on the Hydrogen A

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• 作者：Michela Salamone ; Riccardo Amorati ; Stefano Menichetti ; Caterina Viglianisi ; Massimo Bietti
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：July 3, 2014
• 年：2014
• 卷：79
• 期：13
• 页码：6196-6205
• 全文大小：517K
• ISSN：1520-6904

文摘

A time-resolved kinetic study on the reactions of the cumyloxyl radical (CumO^{鈥?/sup>) with intramolecularly hydrogen bonded 2-(1-piperidinylmethyl)phenol (1) and 4-methoxy-2-(1-piperidinylmethyl)phenol (2) and with 4-methoxy-3-(1-piperidinylmethyl)phenol (3) has been carried out. In acetonitrile, intramolecular hydrogen bonding protects the phenolic O鈥揌 of 1 and 2 from attack by CumO鈥?/sup> and hydrogen atom transfer (HAT) exclusively occurs from the C鈥揌 bonds that are 伪 to the piperidine nitrogen (伪-C鈥揌 bonds). With 3 HAT from both the phenolic O鈥揌 and the 伪-C鈥揌 bonds is observed. In the presence of TFA or Mg(ClO₄)₂, protonation or Mg2+ complexation of the piperidine nitrogen removes the intramolecular hydrogen bond in 1 and 2 and strongly deactivates the 伪-C鈥揌 bonds of the three substrates. Under these conditions, HAT to CumO鈥?/sup> exclusively occurs from the phenolic O鈥揌 group of 1鈥?b>3. These results clearly show that in these systems the interplay between intramolecular hydrogen bonding and Br酶nsted and Lewis acid鈥揵ase interactions can drastically influence both the HAT reactivity and selectivity. The possible implications of these findings are discussed in the framework of the important role played by tyrosyl radicals in biological systems.}