2- Methylquinoxaline reactions

Reaction of nitromalon-bis-A -methylanilide (105) with sulfuric acid gives A -methylisatin- -oxime (107) and not 4-methylquinoxalin-3-one 1-oxide (108) as originally suggested. This transformation may involve a Beckmann-type rearrangement of the protonated aci-nitro compound (106) prior to dehydrative ring closure. ... 

Bromomethyl-2,3-dimethoxy-7-methylquinoxaline (265) underwent a classical Sommelet reaction and incidental hydrolysis of the methoxy groups to give 7-methyl-2,3-dioxo-l,2,3,4-tetrahydro-6-quinoxalinecarbaldehyde (266) (hexamethylenetetramine, CHCI3, 20°C reflux, 30 min solid from evapora-... 

Acetyl-3-methylquinoxaline from its 1,4-dioxide (262) [substrate, Nal, AcMe, 20°C then (F3CC0)20 slowly, extremely rapid reaction 86%] analogs... 

Reaction of 1,2-diaminobenzene with l,l,l-trifluoro-2,3-alkanediones gives trifluoromethylquinoxalines in high yields <2001JHC773>, and that with perfluoro-2,3-butanedione mono(dimethylhydrazone) gives 2,3-trifluoro-methylquinoxaline <2000TL9267>. 

Quinoxaline has been prepared by the reaction of glyoxal with o-phenylenediamine, and 2-methylquinoxaline by the reaction of pyruvic aldehyde or isonitrosoacetone with < -phenylenedi-amine. 2,3-Pyrazinedicarboxylic acid has been prepared only by the permanganate oxidation of quinoxaline. 2-Methyl-5,6-pyrazinedicarboxylic acid has been prepared from 2-methyl-quinoxaline in the same way. - ... 

The UV irradiation of quinoxaline in methanol yields radicals, not by hydrogen abstraction, but by protonation of the first singlet excited state, followed by exiplex formation.82 Irradiation of quinoxaline in acidified methanol furnishes 2-methylquinoxaline, and the reaction is suggested to go through a pathway involving electron-transfer from the solvent to an excited state of the protonated quinoxaline (Scheme 3).83... 

During the last few years, numerous quaternary salts of quinoxalines have been prepared, and their reactions studied. 2-Methylquinoxaline and some of its 6,7-substituted derivatives (101) form 4-methyl-quinoxalinium methosulfates and perchlorates (102).116 On hydrolysis of these salts, the quinoxalinones (103) are formed. Similarly 2,3-dimethyl-... 

Quinoxaline and 2-methylquinoxaline form 1 1 adducts (111) with diphenylcyclopropenone,122 and an analogous pyrrolo[l,2-a]quin-oxaline has been isolated from the reaction of quinoxaline with di-phenylcyclopropenethione.123... 

Quinoxalines substituted in the 5- or 6-position generally follow the pattern of reactions expected for substituted benzene derivatives, although recently there have been reports of interesting and unexpected reactions with nucleophiles (see Section III, A,2 and references 85-90). 6-Methylquinoxaline is brominated in the side chain when treated with N-bromosuccinimide in carbon tetrachloride in the presence of azobisiso-butyronitrile, to form 6-bromomethylquinoxaline.182... 

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... 

Methylquinoxaline also undergoes a novel cycloaddition reaction with two equivalents of tetrachloro-l,2-benzoquinone129 (see Section III,A) with formation of a quinoxaline-orange type product. The reaction probably proceeds by initial formation of the quaternary salt 231 which by elimination of HC1, followed by protonation and dehydration, leads to the cyclized product 232. This on reaction with a further equivalent of tetrachloro-l,2-benzoquinone at the C=N function gives the final yellow compound 117. 

Quinomethionate (91) (60AG973) is made by reaction of 6-methylquinoxaline-2,3-dithiol with carbonyl chloride. It is used to control spider mites, and also has fungicidal properties. An experimental acaricide containing the unusual trifluoromethylimino group is the thiazolidine (92) (72GEP2062348). It is made by reaction of Af.fV -diphenylthiourea with the highly fluorinated intermediate (93). 

Double hydrogenation of 2-methylquinoxaline using (R)-4 with an S/C of 100 under 5 atm of H2 afforded (S)-2-methyl-l,2>3,4-tetrahydroquinoxaline in 90% ee and in a 53.7% yield (Scheme 11) [24]. When the reaction proceeded under lower H2 pressure, a higher optical yield was obtained. The two C=N bonds were hydrogenated at comparable rates. 

Quinoxaline170-172 is reduced to 1,4-dihydroquinoxaline (167) in a reversible reaction. 2-Methylquinoxaline is reduced to 3,4-dihydro-2-methylquinoxaline (168),172 whereas 2-phenylquinoxaline forms l,2-dihydro-2-phenylquinoxaline (169) the 1,4-dihydroquinoxalines may be formed primarily, but are then tautomerized to the more stable dihydroquinoxaline. 2,3-Diphenylquinoxaline is reduced to as-l,2,3,4-tetrahydro-2,3-diphenylquinoxaline, the 1,4-dihydro compound is transformed into the 1,2-dihydro derivative, which is further reducible.172... 

Intermediate 6-substituted quinoxalin-2(l//)-one 4-oxides can be converted into 6-substituted 3-methylquinoxalin-2(l//)-one 4-oxidcs in a one-pot reaction involving dehydration, deacetylation and decarboxylation using ethyl acetoacetate. ... 

Treatment of isonitrosoacetone with 5-fold excess sodium hydrogen sulfite in water followed by the addition of an equimolar amount of benzene-1,2-diamine gives 3-methylquinoxalin-2-amine (mp 163-164°C) in 70% yield. The reaction proceeds through a bis-adduct with the sulfite.In the absence of sodium hydrogen sulfite the yield is only 42%. ... 

Methylquinoxaline and some of its 6,7-substituted derivatives give 4-methylquinoxalin-ium methosulfates and perchlorates. The reactions must be carried out under an inert atmosphere to avoid oxidative dimerization. 2,3-Dimethylquinoxaline is quatcrnizcd with dimethyl sulfate to give 1,2,3-trimethyl quinoxalinium methosulfate. ... 

Chloro-3-methylquinoxaline (7) undergoes reaction with a / ,7-unsaturated Grignard reagent to give the 2-allylquinoxaline derivative 8, which is obtained as an oil. 

Methylquinoxalin-2(l//)-one undergoes reaction with tris(dimethylamino)methane to yield 3-[( )-jS-dimethylaminovinyl]quinoxalin-2(l//)-one... 

Quinoxalin-2-ylmethyllithium (8), prepared by lithiation of 2-methylquinoxaline with lithium diisopropylamide, undergoes an alkylation reaction with bis(trimcthylsilyl)peroxide to yield 2-ethylquinoxaline (9) as an oil. ... 

Bromination of 2-methylquinoxaline using l,3-dibromo-5,5-dimethylhydantoin in the presence of dibenzoyl peroxide (DBPO) under photochemical reaction conditions gives 2-bro-momethylquinoxaline which is a useful synthon for the synthesis of L-quinoxal-2-yiaianine. - ... 

The ring contraction of 2-azido-3-methylquinoxaline 1,4-dioxide (1) to 2 is believed to proceed by an assisted non-nitrene reaction because it proceeds in solution below 100 °C. If the reaction is conducted in toluene at 90 C, however, only compound 3 is formed in 94% yield. ... 

Methylquinoxaline undergoes reaction with Grignard reagents, e.g. ethylmagnesium bromide, phenylmagnesium bromide, to yield 2-alkyl- or 2-aryl-3-methylquinoxaline and 2-alkyl- or 2-aryl-3-methyl-l,2-dihydroquinoxaline. In case of ethylmagnesium bromide, some dimerization product is also formed. ... 

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