- Effect of Blocked ortho-Positions on the Cyclisation of Aryl-1,4-diazabuta-1,3-dienyl Radicals
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Indoles are the main products from the cyclisation of (2,6-dimethylphenyl)-1,4-diazabuta-1,3-dienyl radicals, together with small amounts of quinoxalines; both ring systems arise predominantly via an intermediate spirodienyl radical.
- McNab, Hamish,Smith, Graeme S.
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- Carbon-13 NMR Studies on some 5-Substituted Quinoxalines
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Eleven 5-substituted quinoxalines (NO2, NH2, COOH, OCH3, CH3, OH, F, Cl, Br, I, CN, the latter five not reported previously) have been synthesized by standard methods.Their 13C NMR spectra have been measured in DMSO-d6 and assigned on the basis of substituent parameters, by line widths and by intensities.The chemical shifts compare favorably with those calculated using benzene substituent parameters, and are very close to those of corresponding carbons in 1-substituted phenazines.The correlation with the chemical shifts of the corresponding positions in 1-substituted naphthalenes is also close except for those of carbons 4a and 8a in the quinoxalines which, due to their proximity to nitrogen, are downfield (in some cases 12 ppm) of the signals of the corresponding carbons in naphthalene. 5-Fluoroquinoxaline was also measured in CDCl3, CD3COCD3, CD3CN, CD3OD, C6D6 and CD3COOD.In all solvents an abnormally low 2J(CF) (ca. 12 Hz) was found for C-4a and no C-F spin-spin splitting could be detected for the three-bond coupling of C-8a.Similar abnormalities were found in 2-fluoroaniline and 2-fluoroacetanilide.There are linear relationships between the Q parameter of the substituent and the chemical shift of carbons 4a, 5 and 6.A linear relationship also exists between the chemical shift of C-8 ('para' position) and the Hammett ?p parameter of the substituent.
- Hollstein, Ulrich,Krisov, Galen E.
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- Palladium Nanoparticles Stabilized by Metal–Carbon Covalent Bonds as an Expeditious Catalyst for the Oxidative Dehydrogenation of Nitrogen Heterocycles
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The first method for the dehydrogenation of nitrogen heterocycles catalyzed by a palladium nanocatalyst was developed. Carbon–metal covalent-bond-stabilized nanoparticles were found to be efficient for the dehydrogenation process in the presence of tert-butyl hydroperoxide. A variety of N-heterocycles were transformed into functionalized quinolines in medium to excellent yields in water as the solvent under mild conditions by a simple operation.
- Sun, Xiao-Tao,Zhu, Jie,Xia, Yun-Tao,Wu, Lei
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- Potassium tert-Butoxide-Promoted Acceptorless Dehydrogenation of N-Heterocycles
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Potassium tert-butoxide-promoted acceptorless dehydrogenation of N-heterocycles was efficiently realized for the generation of N-heteroarenes and hydrogen gas under transition-metal-free conditions. In the presence of KOtBu base, a variety of six- and five-membered N-heterocyclic compounds efficiently underwent acceptorless dehydrogenation to afford the corresponding N-heteroarenes and H2 gas in o-xylene at 140 °C. The present protocol provides a convenient route to aromatic nitrogen-containing compounds and H2 gas. (Figure presented.).
- Liu, Tingting,Wu, Kaikai,Wang, Liandi,Yu, Zhengkun
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supporting information
p. 3958 - 3964
(2019/08/01)
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- Acceptorless Dehydrogenation of N-Heterocycles and Secondary Alcohols by Ru(II)-NNC Complexes Bearing a Pyrazoyl-indolyl-pyridine Ligand
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Ruthenium(II) hydride complexes bearing a pyrazolyl-(2-indol-1-yl)-pyridine ligand were synthesized and structurally characterized by NMR analysis and X-ray single crystal crystallographic determinations. These complexes efficiently catalyzed acceptorless dehydrogenation of N-heterocycles and secondary alcohols, respectively, exhibiting highly catalytic activity with a broad substrate scope. The present work has established a strategy to construct highly active transition metal complex catalysts and provides an atom-economical and environmentally benign protocol for the synthesis of aromatic N-heterocyclic compounds and ketones.
- Wang, Qingfu,Chai, Huining,Yu, Zhengkun
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p. 584 - 591
(2018/03/08)
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- Rapid, efficient and eco-friendly procedure for the synthesis of quinoxalines under solvent-free conditions using sulfated polyborate as a recyclable catalyst
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An efficient and inexpensive sulfated polyborate catalyst was applied for the rapid synthesis of quinoxaline derivatives from various substituted o-phenylenediamines and 1,2-diketones/α-hydroxy ketones using sulfated polyborate is described. The catalyst has the advantage of Lewis as well as Bronsted acidity and recyclability without significant loss in catalytic activity. The key advantages of the present method are high yields, short reaction times, solvent-free condition, easy workup, and ability to tolerate a variety of functional groups, which give economical as well as ecological rewards. [Figure not available: see fulltext.]
- Indalkar, Krishna S,Khatri, Chetan K,Chaturbhuj, Ganesh U
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p. 141 - 148
(2017/02/23)
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- Acceptorless dehydrogenation of nitrogen heterocycles with a versatile iridium catalyst
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Gas up: A cyclometalated iridium complex is found to catalyze the dehydrogenation of various benzofused N-heterocycles, thus releasing H 2. Driven by as low as 0.1 mol % catalyst, the reaction affords quinolines, indoles, quinoxalines, isoquinolines, and β-carbolines in high yields. Copyright
- Wu, Jianjun,Talwar, Dinesh,Johnston, Steven,Yan, Ming,Xiao, Jianliang
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supporting information
p. 6983 - 6987
(2013/07/26)
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- The nitration of 8-methylquinoxalines in mixed acid
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8-Methylquinoxalines are nitrated surprisingly efficiently at C-5 following a simple nitration protocol with mixed acid at 40-50°C. The implications of halogen functionalisation at C-6 and modification of the mixed acid conditions on the relative rates of conversion and process safety are discussed. Competing side reactions for 6-halo-8-methylquinoxalines involve hydrolysis at C-6 and halogenation at C-7 or C-5.
- Marterer, Wolfgang,Prikoszovich, Walter,Wiss, Jacques,Prashad, Mahavir
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p. 318 - 323
(2013/09/06)
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- The Thermolysis of Polyazapentadienes. Part 4. Formation of Indoles and Quinoxalines from 5-(2,6-Disubstituted phenyl)-1,2,5-triazapentadienes and Related Compounds
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7-Methylindole and 5-substituted quinoxalines are the principal cyclised products from the qas-phase thermolyses of the hydrazones (2) and (5) and the oxime ester (7).Both heterocyclic systems arise by competitive decomposition of the spirodienyl radical, e.g. (18), the indole by loss of MeCN and a hydrogen atom, and the quinoxalines by loss of a methyl radical.
- McNab, Hamish
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p. 377 - 380
(2007/10/02)
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- 13C Nuclear Magnetic Resonance Spectra of Quinoxaline Derivatives
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The 13C n.m.r. spectra of a series of 5-, 6-, and 2-substituted quinoxalines have been analysed by consideration of their 1H coupled spectra.Typical values of the coupling constants are: C(2,3), 1JCH 181.9, 2JCH 11.4, C(5,8), 1JCH 162.6, 3JCH 6.5, C(6.7), 1JCH 159.4, 3JCH 9.1; C(9), 3JCH(2) = 3JCH(7) = 10.0, 3JCH(5) 5.4; C(10), 3JCH(3) = 3JCH(6) = 10.0, 3JCH(8) 5.4 Hz.The magnitudes of the coupling constants in the benzenoid ring are similar to these for the corresponding positions in naphthalene, but application of naphthalene chemical shift substitutions effects leads in some cases to the wrong peak sequence in the related quinoxalines.Within the quinoxaline series itself, however, acceptable additivity of substituent effects is found (+/- 0.8 p.p.m.), provided that the reference compounds are carefully chosen.Analysis of mixtures of quinoxalines from substituted o-phenylenediamines and α-oxo-aldehydes is possible by consideration of the multiplicity of the ring-junction quaternary carbon signals in the fully coupled spectra.
- McNab, Hamish
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p. 357 - 364
(2007/10/02)
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- The Thermolysis of Polyazapentadienes. Part 2. Formation of Quinoxalines from 5-Aryl-1-phenyl-1,2,5-triazapentadienes
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Thermolysis in the gas phase of 5-(p-substituted phenyl)-1-phenyl-1,2,5-triazapentadienes at 600 deg C and 10-2 Torr gives 6-substituted quinoxalines.The yield is ca. 30 percent, and is independent of the electronic nature of the substituent.The corresponding 5-(o-substituted) derivatives give 5-substituted quinoxalines, though the yield is lower, and quinoxaline itself is a major contaminant, due to ipso attack and ejection of the substituent. 5-(m-Substituted) derivatives give mixtures of 5- and 6-substituted quinoxalines on pyrolysis.The 5-isomer is dominant for compounds with m-alkyl substituents, while the 6-isomer is the major product for those with electron-withdrawing or electron-donating m-substituents.
- McNab, Hamish
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p. 1941 - 1946
(2007/10/02)
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