Binding to Redox-Inactive Alkali and Alkaline Earth Metal Ions Strongly Deactivates the C鈥揌 Bonds of Tertiary Amides toward Hydrogen Atom Transfer to Reactive Oxygen Centered Radicals

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• 作者：Michela Salamone ; Giulia Carboni ; Livia Mangiacapra ; Massimo Bietti
• 刊名：Journal of Organic Chemistry
• 出版年：2015
• 出版时间：September 18, 2015
• 年：2015
• 卷：80
• 期：18
• 页码：9214-9223
• 全文大小：531K
• ISSN：1520-6904

文摘

The effect of alkali and alkaline earth metal ions on the reactions of the cumyloxyl radical (CumO^{鈥?/sup>) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) was studied by laser flash photolysis. In acetonitrile, a >2 order of magnitude decrease in the rate constant for hydrogen atom transfer (HAT) from the C鈥揌 bonds of these substrates (k_H) was measured after addition of Li+. This behavior was explained in terms of a strong interaction between Li+ and the oxygen atom of both DMF and DMA that increases the extent of positive charge on the amide, leading to C鈥揌 bond deactivation toward HAT to the electrophilic radical CumO鈥?/sup>. Similar effects were observed after addition of Ca2+, which was shown to strongly bind up to four equivalents of the amide substrates. With Mg2+, weak C鈥揌 deactivation was observed for the first two substrate equivalents followed by stronger deactivation for two additional equivalents. No C鈥揌 deactivation was observed in DMSO after addition of Li+ and Mg2+. These results point toward the important role played by metal ion Lewis acidity and solvent Lewis basicity, indicating that C鈥揌 deactivation can be modulated by varying the nature of the metal cation and solvent and allowing for careful control over the HAT reactivity of amide substrates.}