2-Quinoxalinecarboxylic acid 4-oxide

Methyl-2-quinoxalinecarboxylic acid 1-oxide 3-Methyl-2-quinoxalinecarboxylic acid 4-oxide... 

Quinoxalinecarboxylic acid 2-Quinoxalinecarboxylic acid 1,4-dioxide 2-Quinoxalinecarboxylic acid 1-oxide 2-Quinoxalinecarboxylic acid 4-oxide 2,3-Quinoxalinediamine... 

Two routes to quinoxalinecarboxylic acids have been covered already by primary synthesis (see Chapter 1) and by oxidation of alkylquinoxalines (see Section 2.2.4). The remaining methods are illustrated by the following classified examples. 

Quinoxalinecarbaldehyde 1-oxide (25) gave initially mainly 2-quinoxaline-carboxylic acid 1-oxide (26) (AcOH, 30% H2O2, 20°C, 24 h %) but subsequently 2-quinoxalinecarboxylic acid 1,4-dioxide (27) (same condi-... 

Reactions of quinoxalinecarbaldehydes that have already been covered include conversion into styrylquinoxalines (Section 2.2.1.3), reduction to hydroxyalkyl-quinoxalines (Section 4.3.1), and oxidation to quinoxalinecarboxylic acids (Section 7.1.1). Other reactions are illustrated by the following examples. 

Ethyl 2-quinoxalinecarboximidate 1-oxide Ethyl 2-quinoxalinecarboxylate Ethyl 5-quinoxalinecarboxylate Ethyl 6-quinoxalinecarboxylate Ethyl 2-quinoxalinecarboxylate 4-oxide 3-Ethyl-2-quinoxalinecarboxylic acid 2-Ethylquinoxaline 1,4-dioxide 2-Ethylquinoxaline 1-oxide 2-Ethylquinoxaline 4-oxide... 

Phenyl-2-quinoxalinecarbonitrile 1,4-dioxide 3-Phenyl-2-quinoxalinecarbonitrile 1-oxide 3-Phenyl-2-quinoxalinecarbonitrile 4-oxide (2 -H 3)-Phenyl-6-carboxamide (mixture) 3-Phenyl-2-quinoxalinecarboxamide 3-Phenyl-2-quinoxalinecarboxamide 1-oxide 3-Phenyl-2-quinoxalinecarboxamide 4-oxide 3-Phenyl-2-quinoxalinecarboxylic acid 3-Phenyl-6-quinoxalinecarboxylic acid 3-Phenyl-2-quinoxalinecarboxylic acid 1,4-dioxide... 

Hydroxy-3-oxo-3,4-dihydro-2-quinoxalinecarbonitrile 4-Hydroxy-3-oxo-3,4-dihydro-2-quinoxalinecarbonitrile 1-oxide 4-Hydroxy-3-oxo-3,4-dihydro-2-quinoxalinecarboxylic acid 1 -Hydroxy-3-phenyl-2( l/f)-quinoxalinone... 

Methoxy-2-quinoxalinecarbonitrile 1,4-dioxide 3-Methoxy-2-quinoxalinecarbonitrile 1-oxide 3-Methoxy-2-quinoxalinecarboxamide 3-Methoxy-2-quinoxalinecarboxamide 1-oxide 3-Methoxy-2-quinoxalinecarboxylic acid... 

Propyl-2-quinoxalinecarboxylic acid /V-Propyl-2,3-quinoxalinedicarboximide 3-Propyl-2(l//)-quinoxalinone 3-Propyl-2(l//)-quinoxalinone 4-oxide 2-Quinoxalinamine... 

III) and urea (II), the quinoxalinecarboxylic acid (III) is decarboxylated to 1-ribityl-l, 2-dihydro-2-keto-6,7-dimethylquinoxaline (IV), which in turn is oxidized to l-ribityl-2,3-diketo-l, 2,3,4-tetrahydro-6,7-dimethylquinoxaline (V). The first two of these proposed reactions would correspond to the chemical degradation of riboflavin or lumiflavin by dilute alkali and heat (cf. Fig. 1, A, B, C). Preliminary experiments with the appropriate quinoxalinecarboxylic acid and its lactam did not lead to their conversion to l-ribityl-2,3-diketo-l,2,3,4-tetrahydro-6,7-dimethylquinoxaline, although the chemical oxidation by hydrogen peroxide of 1-ribityl-l,2-dihydro-2-keto-6,7-dimethylquinoxaline-3-carboxylic acid has been indicated to occur. As a result, the possibility has been considered that products other than those pictured resulting in compounds (III) and... 

Benzenesulfonyl-l-ethoxycarbonylmethyl-3,4-dihydro-2(l//)-quinoxalinone (8) gave either l-carboxymethyl-2(l//)-quinoxalinone (9) (1.25M NaOH, reflux, 6 h 92% note additional nuclear oxidation by loss of PhS02H) or 4-benzenesulfonyl-1 -carboxymethyl-3,4-dihydro-2(lfl)-quinoxalinone (10) (H2 SO4, AcOH, H2O, 80°C, 15 min then 60°C, 5 h then 20°C, 16 h 27%). Methyl 3-methyl-2-quinoxalinecarboxylate 1,4-dioxide (11, R = Me) gave 3-methyl-2-quinoxalinecarboxyhc acid 1,4-dioxide (11, R = H) (Et3N, CaCl2,... 

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