Quinoxaline Sulfoxides and Sulfones

Preparation. A few such derivatives have been made by primary synthesis (see Sections 1.6.7 and 1.8) or by arenesulfinolysis of halogenoquinoxalines (see Sections 3.2.7 and 3.4.4) but most have been prepared by the oxidation of alkyl-or arylthioquinoxalines (see Section 5.2.2). In addition, recently used minor routes are represented in the following examples. 

6-Nitroquinoxaline (61) gave 6-nitro-2-(l-phenylsulfonylethyl)quinoxalme (62) [ClCHMeS02Ph, KOH, Me2SO, 20°C, 5 h 58% a passenger introduction during alkylation).  

Reactions. Although both C-alkylsulfinyl- and C-alkylsulfonylquinoxalines have great potential as versatile intermediates, especially for displacement reactions, they have seldom been used as such in recent years for example, their hydrolysis, alcoholysis, and phenolysis have been totally ignored. However, an example of the conversion of an arylsulfonyl-into a halogenoquinoxaline has been given in Section 3.1.5, and some other reported reactions are illustrated in the following examples. 

7-Dichloro-2-methyl-3-methylsulfonylquinoxahne 1,4-dioxide (63) gave 6,7-dichloro-2-(3-dimethylaminopropylamino)-3-methylquinoxahne 1,4-dioxide (64) (H2NCH2CH2CH2NMe2, CHCI3, dioxane, 20°C 80°C, 10 h 47%) or N, A -bis(6,7-dichloro-3-methyl-l,4-dioxidoquinoxaline-2-yl)hydrazme (65) (H2NNH2, EtOH, 20°C, 10 h 66%).  

Methyl 3-(2-phenylsulfonylethyl)-2-quinoxalinecarboxylate 1,4-dioxide (66) and diethylamine gave only methyl 3-(2-diethylaminoethyl)-2-quinoxalme-carboxylate 1,4-dioxide (67) (Et2NH, MeCN, 20°C, 2 h 40%) ° when ammonia or a primary amine was used similarly, the analogous (unisolated) product (68, R = H or alkyl) underwent spontaneous cyclization to afford, for 

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Oxidation of 2-methyl-3-(methylthio)quinoxaline 1,4-dioxide with 1 equivalent of m-chloroperbenzoic acid yields the corresponding sulfoxide, and 2 equivalents of oxidizing agent gives the sulfone, both products being isolated in good yield. Treatment of the substituted sulfoxide- or sulfone-quinoxaline dioxides with aqueous halogen acids leads to nucleophilic displacement and the formation of 2-haloquinoxaline 1,4-dioxides.199... 

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