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Quinoxalines transfer hydrogenation

The use of air-stable catalyst, a combination of [Cp lrCl2]2 (222) with (223), for selective transfer hydrogenation of quinoxalines in H2O with HC02Na (H2 source) produced corresponding tetrahydroquinoxalines in good to excellent yields. The aqueous phase reduction was highly pH dependent, with acidic pH leading to better results. The HOAc/NaOAc buffer solution was used to maintain the pH of the reaction mixture at which optimum rate was obtained. ... [Pg.173]

Other interesting examples of catalytic transfer hydrogenation have been also described for the transformation of quinoxaline and quinoxalinones into the corresponding 2-tetrahydroquinoxalines 36 (Fig. 4) and 3-dihydroquinoxalinones 37 (Fig. 5) [100], with a structural core which exhibits remarkable biological properties [101-104]. [Pg.123]

Recently, Chen et al. reported a novel hydrogenation of quinoxalines 357 via the convergent disproportionation reaction of dihydroquinoxalines 359 under a ruthe-nium/Br0nsted acid relay catalysis system (Scheme 2.95) [130a]. This transformation was initiated by the reduction of quinoxalines to dihydroquinoxalines 359 under the catalysis of [Rul/i-cymene) ] 360 the active intermediate then underwent phosphoric acid-catalyzed self-transfer hydrogenation to afford primary starting material 357... [Pg.112]

Complexes. The structure of an n a charge-transfer complex between quinoxaline and two iodine atoms has been obtained by X-ray analysis and its thermal stability compared with those of related complexes. The hydrogen bond complex between quinoxaline and phenol has been studied by infrared spectroscopy and compared with many similar complexes. Adducts of quinoxaline with uranium salts and with a variety of copper(II) alkano-ates have been prepared, characterized, and studied with respect to IR spectra or magnetic properties, respectively. [Pg.94]

The UV irradiation of quinoxaline in methanol yields radicals, not by hydrogen abstraction, but by protonation of the first singlet excited state, followed by exiplex formation.82 Irradiation of quinoxaline in acidified methanol furnishes 2-methylquinoxaline, and the reaction is suggested to go through a pathway involving electron-transfer from the solvent to an excited state of the protonated quinoxaline (Scheme 3).83... [Pg.384]

Quinoxalin-2-amine (14) can be synthesized by intramolecular cyclization of (2-aminophcnyl)-aminoacetonitrile (13) to form 3,4-dihydroquinoxalin-2-amine which is then dehydrogenated. The 3.4-dihydroquinoxalin-2-amine need not be isolated for conversion to quinoxalin-2-amine (14). since addition of hydrogen peroxide to the mixture in the presence of a catalytic amount of a transfer agent, such as iron(II) chloride, brings about the required dehydrogenation. ... [Pg.199]

The condensation of a-ketoacids and o-phenylenediamines gives quinoxalin-2-ones,7 and mesoxalic acid and o-phenylenediamine undergo the expected condensation reaction to give quinoxalin-3-one-2-carboxylic acid (1). With sodium mesoxalate an anomalous reaction occurs, the initial products (1) and l,2-dihydrobenzimidazole-2,2-dicarboxylic acid (2) undergo an intermolecular hydrogen transfer reaction to yield l,2,3,4-tetrahydro-3-oxoquinoxaline-2-carboxylic acid (3) and benzimidazole-2-carboxylic acid (4).8... [Pg.205]

The influence of acid on these additions is considerable. In ethanol, for example, ethyl nicotinate is converted into the corresponding 6a-hydroxyethylpyridine, whereas in acidified solution the 6-ethylpyridine derivative is obtained.147 The function of the acid may, of course, simply be to promote dehydration of the intermediate 6a-hydroxyethyldihydropyridine. Phthalazine and quinoxaline are converted by irradiation in acidified methanol into 1-methylphthalazine and 2-methylquinoxaline, respectively.148 In this case, however, there is evidence to suggest that the alkylations proceed by way of electron transfer from the solvent to an excited state of the protonated diazines in neutral solution, a hydrogen... [Pg.451]

Rapala et al. J Am Chem Soc 79 3770 1957], nicotinic acid to hexahydronicotinic (nipecotinic) acid without decarboxylation [2 atmospheres, 25°, 4 hours Freifelder J Org Chem 27 4046 1962, Freifelder J Org Chem 28 602, 1135 1963], complete hydrogenation of quinoxaline [Broadbent at al. J Am Chem Soc 82 189 1960], reduetion of the 4,5-double bond of pyrimidine nucleosides and nucleotides [Cohn Doherty JAm Chem Soc 78 2863 1956], dehydrogenation e g. hydrogen transfer from hexahydrohexahelicene to benzene in order to provide hexahelieene and cyclohexane in 73% yield [Newman Lednicer J Am Chem Soc 78 4765 1956, cf also Anderson Anderson J Org Chem 22 1197 1957], and hydrogenation of anilines to cyclohexylamine with httle hydrogenolysis [Freifelder et al. J Org Chem 30 2485 1965],... [Pg.670]


See other pages where Quinoxalines transfer hydrogenation is mentioned: [Pg.125]    [Pg.336]    [Pg.202]    [Pg.948]    [Pg.948]    [Pg.969]    [Pg.59]    [Pg.205]    [Pg.354]    [Pg.242]    [Pg.354]    [Pg.184]    [Pg.40]    [Pg.670]    [Pg.201]    [Pg.191]   
See also in sourсe #XX -- [ Pg.173 ]




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Quinoxalines hydrogenation

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