2- quin oxaline

Finally the preformed 2-formyl-3-aminoquinoxaline (448) gave the pyrido[2,3-f ]quin-oxalin-2-one (449) with activated esters/sodium alkoxide (79ZC422). 

Little work has been reported on pyrazine-2,3-diones, however spectral evidence has been advanced by HonzL to support the dioxo formulation 126. Dioxo structures have been assigned to quin-oxaline-2,3-dione (127) and its 1-methyl analog on the basis of ultraviolet and infrared spectral data, and according to... 

Attempts to isolate 1,4-dihydroquinoxalinc itself were not successful, but the polarographic behavior of quinoxaline and 6-substituted quin-oxalines in buffered aqueous media suggests that in all cases reduction stops at the 1,4-dihydro stage/ - 2,3-Dimethylquinoxaline and 2-d-araho-tetrahydroxybutylquinoxaline show similar polarographic be-havior, ... 

The infrared spectra of twelve di-, tri-, and tetra-substituted quin-oxalines have also been reported " ... 

Morpholino-3-[4-phenyl(thiosemicarbazido)carbonyl]quinoxaline (129) gave 2-morpholino-3-(4-phenyl-5-thioxo-5,6-drhydro-4//-l,2,4-triazol-3-yl)quin-oxaline (130) (2M NaOH, reflux, 3 h 35%), 2-(5-anilino-l,3,4-thiadiazol-2-yl)-3-morpholinoquinoxaline (131, X = S) (98% H2SO4, 0°C, 1 h, then 20°C, 12 h 89%), or 2-(5-anilino-l,3,4-oxadiazol-2-yl)-3-morpholinoquinoxaline (131, X = O) (NaOH, H2O, EtOH, I/Kii dropwise, 5°C 95°C, 4 h 81%) analogs of all three products were made similarly. ... 

Kurasawa et al. carried out some transformations with the a,/3-unsaturated ester-containing tetrazolo[l,5- ]quin-oxaline moiety 88 (Scheme 16) <1994JHC233>. This compound underwent azo couplings with 2-(iV-methyl)-pyrazinyldiazonium salt in the methylene position to yield hydrazones 89 in high yield. 

New metal complexes other than Ru have also been investigated. These include Fe complexes [117,118], Os complexes [119-122], Re complexes [123], and Pt complexes [124]. A nanocrystalline 2 solar cell sensitized by a square-planar platinum(II) complex containing 4,4 -dicarboxy-2,2 -bipyridine and quin-oxaline-2,3-dithiolate ligands showed an efficiency of 2.6% (Jsc = 6.14 mA/cm2... 

Following extraction/cleanup, quinoxaline-2-carboxylic acid can be detected by electron capture, or mass spectrometric techniques, after gas chromatographic separation on capillary or conventional columns. A prerequisite of quin-oxaline-2-carboxylic acid analysis by gas chromatography is the derivatization of the molecule by means of esterification. Esterification has been accomplished with methanol (419, 420, 422), ethanol (421), or propanol (423) under sulfuric acid catalysis. Further purification of the alkyl ester derivative with solid-phase extraction on a silica gel column (422), thin-layer chromatography on silica gel plate (420), or liquid chromatography on Hypersil-ODS, 3 m, column (423), has been reported. 

Similar rearrangements have been observed on irradiation of quin-oxaline mono- (LXXXIII) and di-X-oxides (LXXXI) in dilute aqueous solution or dilute sulfuric acid,169 of a-9-acridyl-JV -phenylnitrone (LXXXV) moistened with acetone,10 and of LXXXVIT178 forming LXXXII, LXXXIV, LXXXVI, and LXXXVIII, respectively. 

Quinoxaline and 2-methylquinoxaline form 1 1 adducts (111) with diphenylcyclopropenone,122 and an analogous pyrrolo[l,2-a]quin-oxaline has been isolated from the reaction of quinoxaline with di-phenylcyclopropenethione.123... 

Chlorination of 5-hydroxyquinoxaline 1,4-dioxide in methylene chloride gives the 6,8-dichloro derivative, but reaction with N-chlorosuccinimide yields 8-chloro-5-hydroxyquinoxaline dioxide. Bromination in acetic acid gives the 6,8-dibromo derivative.195 15 Side-chain bromination is observed, however, when 2,3-dimethylquinoxaline 1,4-dioxide reacts with bromine in dioxane 2,3-bis(bromomethyl)quin-oxaline 1,4-dioxide is formed.195c... 

There are two possible furoquinoxaline systems, the furo[2,3-6]quinoxaline (201) and the furo[3,4-6]quinoxaline (202). Both types are known. The synthesis of furo[2,3-fe]quin-oxalines has been accomplished by ring closure of suitable 1,4-dicarbonyl units (equation 10) (73CHE239,73MIP31700,79MI31702) which may be employed in a masked form, e.g. (203 ... 

Another report describes the synthesis of pyrazino[2,3-6]quinoxaline 1,4-dioxides (123) by condensation of furoxano[3,4-Z>]quinoxaline (121) with alkynes and alkenes. The pyrazino[2,3-A]quin-oxaline 1,4-dioxides (123) are also isolated as the final products from the reaction with alkenes and oxidation of the initially formed dihydro derivatives (122) (Scheme 21) <88JHC813>. 

Pyrazin 5,6-Dicarboxy-2,3-dihydr-oxy- E9b/2, 342 (2,3-Cl2 —quin-oxalin/KMn04)... 

Some labile quinoxaline-2,3-diyl diphosphites (19) were prepared from quin-oxaline-2,3-diol and characterised by further reactions. Similar diphosphites... 

Photoreduction of some quinoxaline and phenazine -dioxides leads to the major formation of the monooxides as deoxygenation products, in which the reaction has been proved to proceed via radical intermediates by ESR spectroscopy <86H(24)659>. Proton hyperfine structure of quin-oxalines has been observed in glassy matrices and in stretched polyvinyl alcohol films by ESR spectroscopy <87JMR(7i)303>. 

J-Diketones (160) react with benzofuroxan in the presence of triethylamine to form 2-acylquinoxaline dioxides (161). The products from unsymmetrical diketones (160 R R ) have been investigated steric and electronic effects competitively determine which group forms the acyl and which the quin-oxaline substituent, in the product.383 Sometimes deacylation occurs, particularly when a secondary amine is used as the base or when, as with a-substituted /i-diketones (cf. the /J-ketoesters 157), it is necessary for aro-matization.383 387... 

Treatment of quinoxaline-2,3-dicarboxylic acid anhydrides, diesters, or dinitriles with hydrazine monohydrate gives pyridazino[4,5-h]quin-oxalines (Scheme 7). ... 

TABLE 1. 2-ARYL(HETEROARYL)- AND 2,3-DIARYL(DIHETEROARYL)QUIN-OXALINES... 

Qui unci 111 n, f-[[(3-Ca rboxy-2-q u i noxa tinyi)car-bonyl]amino]-3,3-dimethyl-7-oxo-4-thia-l-azabicycto-[3.2.0]heptane-2-carboxylic acid 3-carboxy-2-quinoxaliny[-penicillin. C 6Hl6N30,S mol wt 416.42. C 51.92%, H 3.87%, N 13.46%, O 23.05%, S 7.70%. Semi-synthetic antibiotic related to penicillin. Prepd by condensation of quin-oxaline-2,3-dicarboxylic anhydride with 6 -aminopenicillanic acid Richards et at., Nature 199, 354 (1963). 

Diamines with substituted 1,2,4-triazole and quin-oxaline moieties have been synthesized [77]. The synthesis is shown in Figure 9.14. 

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