Dihydroquinoxalin-2-ones

Treatment of resins 84 with SnCL H2O in DMF at room temperature for 24 h furnished the 3,4-dihydroquinoxalin-2-ones 85 in solution. The filtrates were collected in scintillation vials and concentrated in a centrifugal evaporator. The residues were partitioned between ethyl acetate and 5% aqueous NaOH and sonicated for 5-10 min. The organic layers were removed, dried over anhydrous Na2SO4, filtered into tared scintillation vials, and concentrated once more. 

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Benzopiperazinones 200 were prepared by Erb et al. via the Ugi four-component reaction followed by palladium-catalyzed intramolecular Al-arylation [61]. XPhos was used as a supporting ligand to afford the 3,4-dihydroquinoxalin-3-ones 200 (Scheme 36). Microwave irradiation was found to be determinant on the reaction efficiency. 

Treatment of bis-lactim ether 420 with BuLi, then with cw-l,4-dichloro-2-butene in the presence of Nal afforded 3,4,9,9n-tetrahydro-6//-pyrido[l,2-fl]pyrazin-4-one (421) with 96% diastereomeric excess (97TA1855). Reaction of l,2-diphenyl-6-methyl-quinoxaline with 1,4-dichlorobutane in THF in the presence of Na at —78°C afforded a 3 1 mixture of 4a,5-diphenyl-9-methyl-l,2,3,4-tetrahydro-4a//-pyrido[l,2-n]quinoxaline and 4-(4-chlorobutyl)-2,3-diphenyl-6-methyl-1,4-dihydroquinoxaline (98JHC1349). 

Recent examples of this synthesis are of two types. The first involves condensation of the activated phenol, 2-amino-4,6-dinitrophenol (346a) with 2-dimethyl-amino-3,3-dimethyl-3//-azirine (346b) (in MeCN, 0°C- 20°C, A, 24 h) to afford a separable mixture of four products, one of which was 2-dimethylamino-3,3-dimethyl-5,7-dinitro-3,4-dihydroquinoxaline (346c) ( 20% yield) and another its hydrolysis product, 3,3-dimethyl-5,7-dinitro-3,4-dihydro-2(l//)-quinoxalinone (346d) ( 8%) the mechanism of such condensations has been discussed. ... 

Dihydroquinoxalin-2-one exhibits two successive one-electron oxidation steps in DMF-Bu4NC104.315 Anodic dehydrogenation occurs presumably through an ECE mechanism. 

Reaction of 2-aminopyridine and 3-(jV, Af-dimethylaminocarbony 1) furo[2,3-6]quinoxaline 69 in boiling butanol gave 2-(2-oxo-2//-pyrido [ 1,2-a]pyrimidin-3-yl)-3,4-dihydroquinoxalin-2-one 70 (80CPB3537). 

Reaction of 1,2,4-triazol-4-ylamidines (473) with diethyl carbonate in the presence of sodium ethoxyethoxide led (70JPR669) to intermediate 474 which, upon cyclization, gave the l,2,4-triazolo[3,4-/]l,2,4-triazino-8-ones (475). Kurasawa and his group (85JHC1715) reported that the reaction of 3-(a-hydroxyimino-4-amino-5-methyl-4//-l,2,4-triazol-3-ylmethyl)2-oxo-l,2-dihydroquinoxaline (476) with orthoesters and iron powder in acetic acid gave l,2,4-triazolo[3,4-/]l,2,4-triazines 480 and its 7,8-dihydro isomers 479. 

Dihydroquinoxalin-2(l//)-one oxime (2) in refluxing acetic anhydride yields iV-(2-quinoxa-line)acetamide (3) in 75% yield, and heating of 2 with palladium on charcoal in ethanolic solution gives quinoxalin-2-amine (4) in 82.5% yield. 

Treatment of 2-oxo-l,2-dihydroquinoxaline-3-carbonitrile 4-oxide (1) with aniline, N-methylaniline, or cyclohexylamine results in a displacement of the cyano group and deoxygenation to give 3-substituted quinoxalin-2(127)-ones 2. 

Ethereal CHjNj [from A-mcthyl-A-nitrosotoluene-/)-sulfonamide (see Houben-Weyl. Vol. 10/4, pp 552-553), 21.5 g, 0.1 mol] was added to a stirred, ice-cooled suspension of 6-nitroquinoxalin-2(l//)-one (1.9 g, 9.9 mmol) in anhyd MeOH (20 mL). The mixture was stirred at 0 "C for 4 h, and then left overnight at 0 °C. The precipitate (0.95 g) was filtered off Crystallization (charcoal) from 96% EtOH and then from acetone gave l,3-dimethyl-6-nitro-l,2-dihydroquinoxalin-2(l/f )-one mp 219-222 C. The initial filtrate was evaporated in a vacuum. Crystallization of the residue from light petroleum (bp 60-80°C) and then benzene gave 2-methoxy-6-nitroquinoxaline mpl69-170°C. 

With Zn(OTf)2 (10mol%) as the cocatalyst, the 3,4-dihydroquinoxalin-2-one products 4 were obtained in remarkably increased yields and with excellent en-antioselectivities (>99% ee) in each case (Table 10.1, entries 1-12). It is worth to note that the opposite enantiomer was obtained with similarly high enantioselectivity and yield for the cycloaddition reaction when benzoylquinine (BQN, lb) was used instead of BQD la (entry 13). 

Cyclocondensation between l,2-dihydroquinoxalin-2-ones and l,2,4-triazine-3,5-dione derivatives involves the carbonyl group of the 1,2,4-triazinedione and not the carbonyl group of the quinoxalinones <04JHC597>. New examples of the synthesis of pyridine and 2,2 -bipyridine derivatives from a variety of substituted 1,2,4-triazines through Diels-Alder reactions have been described <04T8893>. 

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