2,3-Dimethylquinoxaline 1,4-dioxide reactions

As a mle, in these reactions, the quinoxaline derivative directly or indirectly fulfills the function of a 1,3-dipolar compound, and this determines the path to the formation of the final product-pyrrolo[l,2-a]quinoxaline-and its structure almost irrespective of the nature of the 1,3-dipolarophile. During the reaction of 2,3-dimethylquinoxaline monooxide 41 and 2,3-dimethylquinoxaline dioxide 44 with methyl phenylpropargylate 42 in molar ratios of 1 1 and 1 2, respectively, compounds 43 and 45 are formed (Scheme 3.15) (Kaupp et al. 1987). 

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... 

Elina and co-workers have extensively investigated the reactions of 2-methylquinoxaline 1,4-dioxide and 2,3-dimethylquinoxaline 1,4-dioxide with aldehydes.206 Under alkaline conditions formalin gives hydroxy-ethyl derivatives, and aryl aldehydes form styrylquinoxalines. As expected, 2,3-dimethylquinoxaline 1-oxide yields 3-methyl-2-styrylquin-oxaline 1-oxide.207... 

Dimethylquinoxaline can be oxidized with peracetic acid in acetic acid to a mono- or di-N-oxide by appropriate choice of reaction conditions. 1,4-Dioxides have also been prepared with this reagent from other 2,3-dialkylquinoxalines, but similar treatment of 2-isopropyl-... 

Selenium dioxide oxidation of 2-methylquinoxaline yields quinoxaline-2-carboxaldehyde, and 3-methylquinoxaline-2-carboxaldehyde has been similarly prepared from 2,3-dimethylquinoxaline. Dimethylsulfoxide oxidation of 2,3-bis(bromomethyl)quinoxaline yields the furoquinoxaline 45, and this on sublimation gives quinoxaline-2,3-dicarboxaldehyde. 3-Dibromomethylquinoxaline-2-carboxaldehyde (46) is a by-product of the oxidation reaction. Direct selenium dioxide oxidation of 2,3-dimethylquinoxaline appears to be a less satisfactory method of preparing the dialdehyde. ... 

Scheme 3.15 Reactions of 2,3-dimethylquinoxaline mono- and dioxides with methyl phenyl-propargylate in various molar ratios...

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