2-Quinoxalinyl ketones

Reactions of 2-chloro- and 2,3-dichloroquinoxalines with carbanions give 2-quinoxalinyl ketones and 3-chloro-2-quinoxalinyl ketones, respectively e.g., 2-quinoxalinylacetophenone (151) from acetophenone anion.161 However, 2,3-dimethoxy- and 2,3-diethoxy-quinoxaline with methyl ethyl ketone and sodamide in anhydrous benzene give 2-amino derivatives rather than ketones.162... 

Some reactions of 2-methylsulfonylquinoxaline (169) have recently been investigated by Hayashi and his co-workers.176 Reaction of 169 with ketones in benzene in the presence of sodamide yields 2-(2-quinoxalinyl) ketones (see Section IV,F149,161) with active methylene compounds, e.g., ethyl cyanoacetate, the 2-substituted quinoxaline (170) is isolated.176 It was also found that reaction of 2-methylsulfonyl-... 

The furo[2,3-b]quinoxalines 20 are formed only in cases where the keto group in the intermediate quinoxalinyl ketone 19 is enolizable. If enolization is not possible, the reaction is completed by the formation of product 19 (Scheme 15) (72YZ736). Therefore, it is not surprising that / -dicarbonyl compounds, which are considerably enolized, undergo a very smooth cyclization with tetrachloropyrazine with ethyl acetoacetate, furo [2,3-b] pyrazine is obtained in good yield (Scheme 15) (83JHC365). 

Reaction of 1-phenylcyclobutene-l,2-dione with benzene-1,2-diamine leads to a quinoxalinyl ketone derivative. 

Quinoxalinyl ketones ean be prepared by condensation of a benzene-1,2-diamine with an appropriate tricarbonyl compound yielding compounds 29. Many syntheses of quinoxaline-2-carbo.xylic acids and their derivatives arc based on the reaction of henzene-1,2-diamine with suitable tricarbonyl compounds. The formation of isomeric mixtures can prove problematic when unsymmetrical diamines arc used in this synthetic approach. 

Ph2MeSBF4 or Ph2MeSC104. These form oxiranes 11 on treatment with carbonyl compounds. Reaction of the oxiranes with LiNEt2 gives quinoxalinyl ketones (12) of the type shown. 

Quinoxalinyl ketones have been prepared by application of the classical quinoxaline synthesis, an o-phenylenediamine being condensed with an appropriate 1,2,3-tricarbonyl compound. Reactions of this type do not provide an unambiguous synthesis of quinoxalinyl ketones, since an alternative mode of condensation is possible leading to a benzo-1,5-diazepinone. The latter possibility is eliminated in the example cited in Scheme 1 because NMR examination of the condensation product... 

The IR spectrum of 2-acetyl-3-methylquinoxaline shows carbonyl stretching absorption at 1695 cm in Nujol and therefore in the region to be expected of an aryl methyl ketone. A range of standard derivatives have been prepared from quinoxalinyl ketones (see Table 1) but cycliza-tion occurs on treatment of various 2-benzoylquinoxalines (10) with... 

Hayashi and his co-workers investigated the reactions of 2-substituted quinoxaline 4-oxides with ketones.210-212 2-Phenylquinoxaline 4-oxide (193) yields 2-phenyl-3-phenacylquinoxaline 4-oxide (203) with acetophenone and sodamide. However, 2-cyanoquinoxaline 4-oxide under these conditions yields cu-(3,4-dihydro-3-oxo-2-quinoxalinyl)aceto-phenone (204) by displacement of the cyano group by the ketone carbanion and rearrangement of the N-oxide.212... 

An alternative to qdt, (.S )-2-(3-mercaptoquinoxalinyl)thiourinium, is stable and soluble in aqueous ethanol solutions unlike qdt (27). At pH 10 in ammonia-ammonium chloride buffer, this reagent hydrolyzes to qdt. (5)-2-(3-Mercapto-quinoxalinyl)thiourinium has been used for the simultaneous detection of nickel and cobalt and the determination of palladium (27, 28). A related reagent, 6-nitro-(S)-2-(3-mercaptoquinoxalinyl)thiourinium has also been used in metal analysis (7). This reagent is hydrolyzed in ammonia buffer to generate 6-nitro-2,3-quinoxalinedithiol (nqdt). Following adjustment to pH 2.0, the mixture is extracted with methyl isobutyl ketone and spectrophotometrically analyzed. 6-Nitro-(5)-2-(3-mercaptoquinoxalinyl)thiourinium has been used for the simultaneous spectrophotometric determination of nickel and cobalt by the quantification of [Ni(nqdt)2]2 (710 nm, e = 20,700 L mol 1cm 1) and [Co(nqdt)2]2 (530 nm, e = 40,000 L moE cm-1), respectively. 

Alkyl and arylmagnesium halides react with 2-methylquinoxaline by addition of one mole of reactant to the 3,4-bond. After hydrolysis the 2-alkyl- or 2-aryl-l,2-dihydro-3-methylquinoxalines (52) are obtained. When ethylmagnesium bromide is used a dimeric by-product (53) is also isolatedReaction of 2,3-dimethylquinoxaline with benzonitrile and lithium amide gives l-amino-l-phenyl-2-(3-methyl-2-quinoxalinyl)-ethylene (54). The mono- and dilithium salts of 2,3-dimethylquinoxaline have been generated from the quinoxaline by reaction with one or two equivalents of lithium diisopropylamide (LiNPr, respectively. These salts have been reacted with a variety of electrophilic reagents such as alkyl halides, aryl ketones, esters, and nitriles. " ... 

Upon thermolysis 5-aryl-4-quinoxalinyl-2,3-dihydro-2,3-furandiones [3-aryl-2-(2-aryl-4,5-dioxo-4,5-dihydro-3-furyl)quinoxalines] 223 leads to decarbonylation and formation of 3-aryl-2-quinoxalinyl(aroyl)ketenes 224, which can be captured using cychc ketones such as cyclopentanone... 

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