Dual Modes of Catalysis of Novel α-Hydrogen Nitroxides
2Chemistry Department, Ariel University, Ariel, Israel
The nature and use of nitroxide compounds as stable radicals and as reactive reagents and catalysts for redox reactions gives them a unique place in organic chemistry.[1] They have been used as radical trapping reagents, catalysts for oxidation of alcohols into carbonyl compounds and allylic transposition reactions.
One of the most efficient and widely used nitroxides is TEMPO (1). However, it has limited reactivity do to its highly hindered structure. A logical way to diminish the steric congestion is to replace an α-alkyl substituent with a hydrogen.
We have developed a new concept for designing stable α-hydrogen nitroxyl radicals.[2] Following the guidelines of this concept we have prepared and studied two new families of nitroxyl radicals namely IINO (2) and IAPNO (3). [3]
Moreover, we were able to examine their activity in anaerobic and aerobic oxidations of alcohols. [4] In each case the catalytic cycle and the reactive species are different. For instance in aerobic oxidation one electron oxidant is essential (copper complex), however, in anaerobic oxidation two electron oxidants is essential (TCCA). (Figure 1)
[1] L. Tebben, A. Studer, Angew. Chem. Int. Ed. 2011, 50, 5034-5068.
[2] M. Amar, S. Bar, M. A. Iron, H. Toledo, B. Tumanskii, L. J. W. Shimon, M. Botoshansky, N. Fridman, A. M. Szpilman, Nat Commun 2015, 6.
[3] H. Toledo, M. Amar, S. Bar, M. A. Iron, N. Fridman, B. Tumanskii, L. J. W. Shimon, M. Botoshansky, A. M. Szpilman, Org. Biomol. Chem. 2015, 13, 10726-10733.
[4] S. Bar, J. N. Kumar, M. Amar, H. Toledo, R. J. Batrice, A. M. Szpilman, ChemCatChem 2015, 7, 1129-1134.
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