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Deoxygenation of aza-aromatics

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A convenient and chemoselective method for deoxygenation of pyridine N-oxide derivatives by transfer oxidation of triethylamine under microwave irradiation is catalysed by [Pd(OAc)2]/dppf.
J. A. Fuentes, M. L. Clarke, Synlett, 2008, 2579-2582.


An electrochemical deoxygenation of N-heteroaromatic N-oxide provides the corresponding N-heteroaromatics such as pyridines, quinolines, isoquinolines, and phenanthridines efficiently in aqueous solution without the need for transition-metal catalysts and waste-generating reducing reagents.
P. Xu, H.-C. Xu, Synlett, 2019, 30, 1219-1221.


Sulfoxides and aza-aromatic N-oxides were deoxygenated using a system of indium and pivaloyl chloride at room temperature to give the corresponding sulfides and aza-aromatics in high yields.
E. S. Park, S. Hwan, Lee, J. H. Lee, H. J. Rhee, C. M. Yoon, Synthesis, 2005, 3499-3501.


A mild and efficient general method for the deoxygenation of organic N-oxides such as azoxybenzenes, N-arylnitrones, and N-heteroarene N-oxides uses the  environmentally friendly Lewis acids Zn(OTf)2 and Cu(OTf)2.
A. Saini, S. Kumar, J. S. Sandhu, Synlett, 2006, 395-398.


Visible light-mediated metallaphotoredox catalysis enables a highly chemoselective deoxygenation of N-heterocyclic N-oxides using Hantzsch esters as the stoichiometric reductants and only a tiny amount of the catalyst within a few minutes at room temperature. The reaction tolerates a wide range of functional groups, such as carbamates, esters, ketones, nitrile groups, nitro groups, and halogens.
J. H. An, K. D. Kim, J. H. Lee, J. Org. Chem., 2021, 86, 2876-2894.


Visible-light mediates a scalable and operationally simple method for the chemoselective deoxygenation of a wide range of N-heterocyclic N-oxides at room temperature using only commercially available reagents. This protocol offers an unprecedented chemoselective removal of the oxygen atom in a quinoline N-oxide in the presence of a pyridine N-oxide through the judicious selection of the photocatalyst.
K. D. Kim, J. H. Lee, Org. Lett., 2018, 20, 7712-7716.