1- Methylquinoxaline-2,3-dione

Peracetic acid oxidation of l-methylquinoxalin-2-one (42) at 55°C gives l-methylquinoxaline-2,3-dione (43) in moderate yield, and similar treatment of l,3-dimethylquinoxalin-2-one (44) yields a small quantity of the 4-oxide, An improved yield of (43) is obtained by... 

Oxidation of 4-methylquinoxalin-3-one 2-carboxy-fV -methylamlide (45) with hydrogen peroxide and acetic acid furnishes the 1-oxide but, on removal of either or both of the fV-raethyl groups (giving 46, 47, or 48), oxidation with hydrogen peroxide or with peracetic or perbenzoic acid results in the removal of the carboxyamide groups and the formation of a quinoxaline-2,3-dione. ... 

Treatment of an alkaline solution of quinoxalin-2-one or quinoxa-line-2,3-dione with an alkyl iodide or sulfate results in A-methylation. Thus methylation of 3-aminoquinoxalin-2-one (74) with methyl sulfate and alkali gives 3-amino-l-methylquinoxalin-2-one (75) and not as previously reported the isomeric 0-methyl derivative. ... 

Methylquinoxaline-2,3-dione (173) is oxidized with Co(OAc)2 Mn(OAc)2 in HBr/H20 to the 6-carboxylic acid (174),183 which on treatment with thionyl chloride is converted into 2,3-dichloro-quinoxaline-6-carbonyl chloride (175).184 The 6-sulfonyl chloride is obtained from quinoxaline-2,3-dione and chlorosulfonic acid and treatment of the resulting 6-chlorosulfonyl derivative with phosphoryl chloride and pyridine.185 Such derivatives are useful synthetic dye intermediates. 

Substituted quinoxalines afford mono-A-oxides, presumably the 1-oxides, and are resistant to further oxidation, though 5-methoxyquin-oxaline is exceptional in forming a 1,4-dioxide. In the case of 6-substituted quinoxalines, as the substituent becomes more electron attracting, the yields of 1,4-dioxide decrease but more of the corresponding 2,3-dioxo compound (41) is formed.50 55 Peracetic acid oxidation of l-methylquinoxalin-2-one (42) at 55°C gives l-methylquinoxaline-2,3-dione (43) in moderate yield, and similar treatment of l,3-dimethylquinoxalin-2-one (44) yields a small quantity of the 4-oxide.56 An improved yield of (43) is obtained by... 

C and addition of excess of potassium iodide to the product, gives only a small yield of methiodide, but 2-acetamidoquinoxaline 4-methiodide (67) is readily prepared by this method. Proof that quaternization occurs at position 4 is obtained by degradation of (67) by boiling alkali to l-methylquinoxaline-2,3-dione and 1 equivalent of ammonia. Similar treatment of the 1-methiodide would yield l-methylquinoxalin-2-one, and under these conditions this compound is not converted into the dione.9... 

If disubstituted maleic anhydride is used in this reaction, even with boiling in toluene solution for 46 h, the process does not go past the stage of formation of the corresponding derivative of succinic acid-3-[(3-methylquinoxalin-2-yl)methyl]-3,4-diphenyldihydrofuran-2,5-dione 55 (Fig. 3.4), which is isolated with a yield of 90 % (Cheeseman and Tuck 1965a). 

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