5-Carboxy-2,3-diphenylpyrazine

Many derivatives of carboxy chloropyrazines have been prepared by the action of phosphoryl chloride on the corresponding hydroxypyrazine. In this way were prepared 2-chloro-3-methoxycarbonylpyrazine (371, 423, 836), 2-chloro-3-methoxycarbonyl-5,6-diphenylpyrazine (but the corresponding hydroxy compound did not react with phosphorus tribromide) (837), and 3-chloro-2-methoxycarbonyl-... 

Alkaline hydrolysis of 2,5-dicyano-3,6-diphenylpyrazine gave 2-carboxy-5-hydroxy-3,6-diphenylpyrazine, and analogous reactions were observed with the... 

Diacetyl-3,6-dibenzylpiperazine-2,5-dione (15) reacted with sulfur in dimethyl-formamide and triethylamine to form, after hydrolytic removal of the acetyl groups, 3-benzyl-6-benzylidenepiperazine-2,5-dione (16) (1068). 2-Chloro-5-hydroxy-3,6-dimethylpyrazine heated with solid potassium hydroxide gave 3-hydroxy-2,5-dimethylpyrazine (312), and 2-chloro-6-hydroxy-3,5-diphenylpyrazine with an excess of methanolic sodium methoxide at 150° formed 2-hydroxy-3,5-diphenylpyrazine (873). Decarboxylation of 2-carboxy-3-hydroxypyrazine gave 2-hydroxypyrazine (420) and in this way 24iydroxy[2- C]pyrazine (823) and 2-hydroxy[l- N]pyrazine (822) have been prepared. 

Chloro-3-methoxycarbonyl-5,6-diphenylpyrazine refluxed with sodium methoxide gave 2-carboxy-3-methoxy-5,6-diphenylpyrazine (371) and the attempted Schmidt reaction of 2,5-dimethoxycarbonylpyrazine, in concentrated sulfuric acid with trichloroacetic acid at 60° with subsequent addition of sodium azide, gave 2,5-dicarboxypyrazine (1176). 2-Methoxy-3-methoxycarbonyl-5,6-diphenylpyrazine, when refluxed with cuprous chloride in dry dimethylformamide, gave 2-carboxy-3-methoxy-5,6-diphenylpyrazine (10%) 2-hydroxy-3-methoxycarbonyl-5,6-diphenyl-pyrazine similarly treated gave 5-hydroxy-2,3-diphenylpyrazine (30%) (837). 

Carboxy-3-(o-carboxyphenyl)-5,6-diphenylpyrazine has been reported to be oxidized by hydrogen peroxide in boiling acetic acid to 2-carboxy-3-(o-carboxyphenyl)-5,6-diphenylpyrazine A-oxide (399). Oxidation of 3- D-arabo-tetrahydroxybutyl)pyrazine 1-oxide with potassium permanganate in aqueous potassium hydroxide gave 3-carboxypyrazine 1-oxide (543). 

Carboxy-3-(o-carboxyphenyI)-5,6-diphenylpyrazine A -oxide was deoxygenated by stannous chloride (399) and 2-carboxy-3,5-bis(methylamino)-6-A -methyl-carbamoylpyrazine 1-oxide with sodium dithionite in aqueous ethanol at 90° for 3 hours (462). 

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