N-Heteroaromatic compounds

Fetzner, S., Enzymes Involve in the Aerobic Bacterial Degradation of N-Heteroaromatic Compounds Molybdenum Hydrolases and Ring Opening 2, 4-Dioxygenases. Naturwis-senschaften, 2000. 87 pp. 59-69. 

N-Heteroaromatic compounds like pyridine, pyridazine, pyrazine, isoquinoline, and their derivatives42,250 react with diphenyl cyclopropenone in a formal (3+2) cycloaddition mode to the C=N bond of the heterocycle. As expected from the results discussed earlier (p. 67), the reaction is initiated by attack of nitrogen at the cyclopropenone C3 position and followed by stabilization of the intermediate betaine 390 through nucleophilic interaction of the Cl/C3 bond with the activated a-site of the heterocycle, giving rise to derivatives of 2-hydroxy pyrrocoline 391—394). In some cases, e.g. diphenyl cyclopropenone and pyridine42, further interaction with a second cyclopropenone molecule is possible under the basic conditions leading to esters of type 392. 

Data pertaining to affinity of organic N-bases towards nitrosonium cation are numerous 74-80), however, those for N-heteroaromatic compounds are limited 77-80). 

A linear relationship between calculated An0+ values and experimental values of proton affinity (PA) for N-heteroaromatic compounds was also established (Figure 3). the points 1-4 (compounds 32h, 46, 32d and 31d respectively) have been excluded from the statistical treatment, r = 0.969]. 

Figure 3. Correlation between the affinity of N-heteroaromatic compounds for NO cation (A no ) and proton affinity (PA).

Supported vanadium oxides represent one of the technologically most important class of solid catalysts. These catalysts are useful for partial oxidation of various hydrocarbons 0), ammoxidation of alkyl substituted N-heteroaromatic compounds (2) and most recently for NO reduction (3) For a catalyst to be a successful one in industry, it should exhibit high activity with maximum selectivity, thermal and mechanical stability and long life etc. For getting some of these functionalities, the active component has to be dispersed uniformly on a support material. 

Many anionic o-adducts have been described as obtained from the interaction of N-heteroaromatic compounds with the amide ion in liquid ammonia. The reaction is often followed by decomposition leading to overall substitution (amination). This held has been intensively investigated by van der Plas, Zoltewicz, and co-workers. 

The Electronic Absorption and Luminescence Spectra of N-Heteroaromatic Compounds and Their Derivatives R. N. Nurmukhametov, Russ. Chem. Rev. (Engl. Transl.), 1967, 36, 693-709. 

The principal tautomeric properties of the fundamental biological pyrimidines—cytosine, uracil, and thymine—are due to the presence in these N-heteroaromatic compounds of electron-donor substituents such as NH2 and OH and of SH in some important analogs. The labile hydrogen may remain attached at the exocyclic 0, N, or S atom or migrate to one of the ring nitrogens, giving rise to three principal types of tautomerism (Scheme 1) ... 

C—H bond alkenylations, 10, 222—223 in cross-coupling polymerization, 11, 687 N-Heteroaromatic compounds, hydrogenation, 1, 792 Heteroaromatic stannanes, preparation, 3, 828 Heteroaryl halides, aminocarbonylatioon, 11, 527 Heteroarylstannanes, preparation, 3, 826 Heteroatoms... 

Table 3. Dicationic species (108-113) arising from diprotonation of N-heteroaromatic compounds.

Radical reactions of protonated N-heteroaromatic compounds 93G9. 

Free-radical substitution of N-heteroaromatic compounds 89H(28)489 90JHC79. 

N-Oxidation of weakly basic N-heteroaromatic compounds. N-Oxidation of poly-halogenopyridincs is difficult owing to the low basicity of the nitrogen atom. For example, treatment of pentachloropyridine with trifluoroacctic acid and 90 % hydrogen peroxide under optimum conditions gives only a 20% yield of the l-oxide. Chivers and Suschitzky now find that the oxidation can be effected in 95% yield by u.se of 90% hydrogen peroxide, acetic acid, and concentrated sulfuric acid. The more expensive trifluoroacetic acid can also be used but with no improvement in yield. No oxidation occurs with use of 75% aqueous sulfuric acid. The function of the sulfuric acid is probably to protonate the peracid and hence facilitate transfer of OH. ... 

Tagawa, Y., Yamashita, K., Higuchi, Y., Goto, Y. Improved oxidation of an active methyl group of N-heteroaromatic compounds by selenium dioxide in the presence of tert-butyl hydroperoxide. Heterocycles 2003, 60, 953-957. 

The polarography and cyclic voltammetry of quinazoline were reported, and the reversible half-wave potential was compared with those of other N-heteroaromatic compounds. The observed energy differences be-... 

N-Oxidation of amines. N-Oxides of tertiary amines or of N-heteroaromatic compounds can be obtained in high yield by N-oxidation with the H202/urea adduct in combination with phthalic anhydride (1 1), which is more effective than acetic or benzoic anhydride. Yields are generally >80%. 

The hydrogenation of N-heteroaromatic compounds is of interest in relation to HDN, since selective hydrogenation of the nitrogen-containing rings always takes place prior to C-N bond breaking (see Scheme Few... 

Although acetonitrile is a common solvent in aryne chemistry, it is rarely involved as a reactant in the coupling reactions with arynes. Recently, a three-component coupling of arynes, N-heteroaromatic compounds, and nitriles was reported by Jeganmohan and Cheng (Scheme 12.18) [42] where the reachon was initiated by a nucleophilic attack of the N-heteroaromatic on the aryne, leading to a zwitterionic species 50. The zwitterion 50 then abstracted a proton from acetonitrile (or other nitrile) to afford intermediate 51, alongside anion 52. Anion 52... 

Misek, J., Teply, F., Stara, I.G., et al. (2008) A straightforward route to helically chiral N-heteroaromatic compounds practical synthesis of racemic 1,14-diaza[5]helicene and optically pure 1- and 2-aza [6]helicenes. Angewandte Chemie International Edition, 47(17), 3188-3191. 

Dimerizations of p-Rich N-Heteroaromatic Compounds and Xanthine Derivatives. Sekine, Toshikazu Higuchi, Yoshihiro Yamada, Tomoko Murakoshi, Isamu (Fac. Pharm. Sci., Chiba Univ., Chiba, Japan 260). Chem. Pharm. BuU. 1989, 37 (8) 1987-9 (Eng.). N-Methylimidazole, benzimidazole, and N-methylbenzimidazole condensed dehydrogenatively to afford the corresponding sym. dimers when heated in the presence of Pd-Pt/C catalyst and pyridine N-oxide. Imidazole, pyrazole, and N-methylpyrazole did not dimerize under the same conditions. The same reactions using caffeine and 1,7-dimethylhypoxanthine gave the eorresponding dimers. 

---