Heteroaromatic V-oxidation

During the last 10 years many additional oxaziridines have been isolated after photolysis of nonaromatic nitrones. The three-membered ring isomers of heteroaromatic /V-oxides proved to be too reactive for direct detection but... 

Troilina, V.S., Sheinker, V.N., Gamovskii, A.D. and Osipov, O.A. (1977) Study of structure and properties of heterocychc compounds and their complexes. XXXV. Study of complexing of heteroaromatic V-oxides with halogens. Si. Obshch. Khim., 47, 642-646. 

V-Oxides of heteroaromatic compounds are generally electrolytic-ally reducible in acid solution242-254 the most studied compounds of this type are the pyridine A-oxides.242 249, 250 At low pH pyridine A-oxide gives a two-electron polarographic wave, but at pH > 4 the wave height diminishes, as the preprotonation step becomes too slow [Eq. (9)]. 

The action of N-oxides of a-dimethylaminocarboxylic acids on dihydroxyphenylborane produces the internal chelates of the oxidation products. Various pyridine and quinoline V-oxides may be used to oxidize organylboranes, but there can be some alkylation of the heteroaromatic rings. ... 

Azo Compounds, Azirines, Diazirines, Diazo Compounds, Diazonium Salts, Azides,. V-Oxides, Nitrite Esters and Heteroaromatic Compounds Photofragmentation and Photorearrangement... 

Recently, the C-H bond of nitrogen heteroaromatics has been shown to become activated upon the conversion of the heteroaromatic to its corresponding /V-oxide derivative (for recent examples of direct functionalization of pyridine /V-oxides and /V-iminopyridiniuin ylides, see [63-67]). Li and co-workers demonstrated that tert-butyl peroxides can mediate the oxidative coupling between pyridine /V-oxides 67 and cycloalkanes 62 (Scheme 36) [68]. 

Certain heteroaromatic compounds that have acidic methyl groups are effective in the Knoevenagel condensation. 6-Methyl-1,3,5-triazine (156), 2-methylpyridine V-oxides (157), quinolines and pyrimidines all condense with aromatic aldehydes in the presence of the usual catalysts. An example of a doubly activated methylene compound in which one activation group is a heterocycle is the 2-oxopro-pylthiazole (158), which condenses with a number of aldehydes. " ... 

The first reduction wave for phenanthridine V-oxide in dimethyl-formamide (at 25°) appears at —1.774 (vs. s.c.e.) in good agreement with the HMO energy of the lowest vacant orbitaH a mechanism for the reduction has been proposed. No esr signal could be detected during controlled-potential electrolysis at the appropriate potential, perhaps because of the relative instability of the anion radical. This behavior, which is paralleled by isoquinoline, contrasts sharply with that of the oxides of other polynuclear N-heteroaromatic systems (e.g., quinoline and acridine). 

V. P. Litvinov, T. V. Shchedrinskaya, P. A. Konstantinov, and Ya. L. Gol dfarb, Condensed heteroaromatic sytems including the thiophene ring. 33. Catalytic liquid-phase oxidation of 3-methyl-substituted thieno[2,3-h]thiophene and thieno[3,2-h]thiophene. Khim. Geterotsikl. Soedin., 492 (1975). 

Electrophilic Substitution in the Series of Six-Membered Nitrogen-containing Heteroaromatic Compounds and Their N-Oxides Zh. I. Aksel rod and V. M. Berezovskii, Russ. Chem. Rev. (Engl. Transl.), 1970, 39, 627-643. 

The unsubstituted TTE 16 is nonaromatic, in the Hiickel sense. Oxidation to the cation radical and dication occurs sequentially and reversibly at relatively low potentials ( 1/2 = 0.37 V and 1/2 = 0.67 V vs. SCE in 147t-electron system. In contrast to the neutral TTF, both the cation radical and dication are aromatic as a result of the brt-electron heteroaromaticity of the 1,3-dithiolium cation. The radical cation and dication can be isolated as stable crystalline compounds due to the effective resonance stabilization of the aromatic dithiolium and, to a minor extent, the polarizable sulfur atoms <1996SR1, 1997SL1211, 1999PS99, 2001AGE1372>. 

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