Journal
JOURNAL OF ORGANIC CHEMISTRY
Volume 80, Issue 18, Pages 9214-9223Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.joc.5b01661
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- Ministero dell'Istruzione dell'Universita e della Ricerca (MIUR) [2010PFLRJR]
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The effect of alkali and alkaline earth metal ions on the reactions of the cumyloxyl radical (CumO(center dot)) 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-H 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-H bond deactivation toward HAT to the electrophilic radical CumO(center dot). 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-H deactivation was observed for the first two substrate equivalents followed by stronger deactivation for two additional equivalents. No C-H 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-H 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.
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