Nitrogen-centered radical-mediated

Other methods, among which thermolysis or photolysis of tetrazene [59], photolysis of nitrosoamines in acidic solution [60], photolysis of nitrosoamides in neutral medium [61], anodic oxidation of lithium amides [62], tributylstannane-mediated homolysis of O-benzoyl hydroxamic derivatives [63, 64], and spontaneous homolysis of a transient hydroxamic acid sulfinate ester [65] could have specific advantages. The redox reaction of hydroxylamine with titanium trichloride in aqueous acidic solution results in the formation of the simplest protonated aminyl radical [66] similarly, oxaziridines react with various metals, notably iron and copper, to generate a nitrogen-centered radical/oxygen-centered anion pair [67, 68]. The development of thiocarbazone derivatives by Zard [5, 69] has provided complementary useful method able to sustain, under favorable conditions, a chain reaction where stannyl radicals act simply as initiators and allow transfer of a sulfur-containing... 

Most polymerizations in this section can be categorized as stable (free) radical-mediated polymerizations (sometimes abbreviated as SFRMP). In the following discussion systems have been classed according to the type of stable radical involved, which usually correlates with the type of bond homolyzed in the activation process. Those described include systems where the stable radical is a sulfur-ccntcrcd radical (Section 9.3.2), a scicnium-ccntcrcd radical (Section 9.3.3), a carbon-centered radical (Sections 9.3.4 and 9.3.5), an oxygen-centered radical (Sections 9.3.6, 9.3.7), or a nitrogen-centered radical (Section 9.3.8). Wc also consider polymerization mediated by cobalt complexes (Section 9.3.9) and certain monomers (Section 9.3.5). 

Another possible pathway for reactivity via nitrogen-centered radical cation intermediates involves delocalization of the radical the aromatic substituents. In 2013, Collins and coworkers [36] reported the visible-light-mediated photoredox synthesis of carbazoles from arylamines 117 through C-H activation and C-C bond formation. A possible mechanism for this conversion is depicted in Scheme 13.18. The excited sensitizer [Cu(Xantphos)(dmp)] is reduced by I2, generating a radical dication [Cu(Xantphos)(dmp)] (dmp 2,9-dimethyl-1,... 

Recently, Lee and coworkers found that nitrogen-centered radicals could be generated from commercially available N-chlorophthalimide with low photocatalyst loadings. By this method, the direct C-H imidation of pyridines was achieved through visible-light-mediated photoredox catalysis (Scheme 13.39) [75]. 

HOCl-mediated protein oxidation accelerates under pathophysiological conditions. Thus, proteins from extracellular matrix obtained from advanced human atherosclerotic lesions contained the enhanced levels of oxidized amino acids (DOPA and dityrosine) compared to healthy arterial tissue [44], It was also found that superoxide enhanced the prooxidant effect of hypochlorite in protein oxidation supposedly by the decomposition of chloramines and chlor-amides forming nitrogen-centered free radicals and increasing protein fragmentation [45], In addition to chlorination, hypochlorite is able to oxidize proteins. The most readily oxidized amino acid residue of protein is methionine. Methionine is reversibly oxidized by many oxidants including hypochlorite to methionine sulfide and irreversibly to methionine sulfone [46] ... 

Carbon-Nitrogen Bond Formation. Apart from the CAN-mediated reactions in which solvent (e.g., acetonitrile) incorporation results in carbon-heteroatom bond formation, the oxidative generation and subsequent addition of heteroatom-centered radicals to alkenes or alkynes provide means of direct construction of carbon-hetereoatom bonds. ... 

The presence of a single unpaired electron primarily residing in the Jt antibonding orbital (polarized toward the nitrogen center) gives rise to a bond order of 2.5 and defines the reactivity of NO. This diatomic gas exerts its effect selectively and mediates signal transductions by reacting with heme Fe centers, nonheme Fe centers (NHI), radical molecules, and thiols. NO... 

In 2014, Yu and coworkers used the hydroxylamine derivative Af,0-ditosyl-JV-methylhydroxylamine 273 as a tunable nitrogen source for the direct C-H amida-tion of heteroarenes through a visible-light-mediated photocatalytic method (Eq. (13.28)) [77a]. A variety of heteroarenes, such as indoles, furans, and pyrroles, smoothly underwent this amidation reaction at room temperature. Very recently, Studer successfully introduced Af-aminopyridinium salts, which are readily prepared from cheap starting materials, as efficient Af-centered radical precursors. These novel Af-radical precursors can be used for the direct C-H amidation of... 

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