Quinoxaline-2,3-dicarboxylic acids preparation

The cleavage of fused pyrazines represents an important method of synthesis of substituted pyrazines, particularly pyrazinecarboxylic acids. Pyrazine-2,3-dicarboxylic acid is usually prepared by the permanganate oxidation of either quinoxalines or phenazines. The pyrazine ring resembles the pyridine ring in its stability rather than the other diazines, pyridazine and pyrimidine. Fused systems such as pteridines may easily be converted under either acidic or basic conditions into pyrazine derivatives (Scheme 75). 

Quinoxaline Derivatives Which Can Be Oxidized to Pyrazine-2,3-dicarboxylic Acids on a Preparative Scale... 

Pyrazinecarboxylic acid has been obtained by selenious acid oxidation in pyridine of methylpyrazine or aqueous permanganate oxidation of ethylpyrazine, in yields of 64 and 48%, respectively.171,218 It has also been obtained in 70% yield by partial decarboxylation of pyrazine-2,3-dicarboxylic acid on heating in vacuo at 210°.219 Aqueous permanganate oxidation of 2,5-distyrylpyrazine gives the 2,5-dicarboxylic acid.220 Pyrazine-2,5-dicarboxylic acid has also been prepared in 45% yield by direct carboxylation of pyrazine with carbon dioxide at 50 atm pressure at 250° for 3 hours in the presence of a potassium carbonate and calcium fluoride catalyst.221 Pyrazine-tricarboxylic acid (57), obtainable in only very poor yields by oxidation of 2,5-dimethyl-3-ethylpyrazine, is prepared in 87% yield by alkaline permanganate oxidation of 2-(D-arabo)tetrahydroxybutyl-quinoxaline (56).222 Decarboxylation of the tricarboxylic acid by... 

The X-ray crystal structures of pyrazine V.JV -dioxide (134) <02AX(E)1253>, the P-polymorph of phenazine (135) <02AX(C)181>, cobalt(III) complexes of pyrazine-2,6- and pyridine-2,6-dicarboxylic acids <02JIC458>, and bis-urea-substituted phenazines <02ZN(B)937> were reported. Fluorescent pyrido[l,2-a]quinoxalines 136 prepared as pH indicators were examined by X-ray crystallography <02JCS(P2)181>, as were macrocyclic quinoxaline-bridged porphyrinoids obtained from the condensation of dipyrrolylquinoxalines 137 and 1,8-diaminoanthracene... 

The mass spectra of some formyl derivatives of 2-(2 -thienyl)indole have been elucidateThe electroreduction of 4-(2-thienyl)quinoxaline has been further investigated. The preparation of 2,5-bis(benzoxazolyl)-thiophens from thiophen-2,5-dicarboxylic acid has been patented... 

The original method of synthesis of [fl5-di(4-ieh-butylbenzo)diquinox-alinoporphyrinato]zinc(II) 188 involves the interaction of excess quinoxaline-2,3-dicarboximide 186, and malonic acid in the presence of zinc(II) acetate with the 5-iert-butyl-3-(5-tert-butyl-3-oxo-2,3-didihydro-lH-isoindol-l-ylidenemethyl)-lf/-isoindol-l-one 187 (2007RJOC1080). In this case imide 186 has been prepared by passing dry NH3 through molten quinoxaline-2,3-dicarboxylic acid at 250 °C over 10 min. 

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