2- Phenyl-3,4-dihydroquinoxaline

Note These synthons will usually give hydroquinoxalines, but some such products may undergo aerial aromatization during the reaction or workup. 1,2-Benzenediamine (129) gave 2-phenyl-3,4-dihydroquinoxaline (130) (AcONa, MeOH, reflux, CH4I, 2 h 55% with unsymmetric analogs of substrate (129), two isomers resulted in each case and the kinetics of such... 

Note Such deoxygenation is usually accompanied by partial nuclear reduction. 3-phenyl-2(177)-quinoxalinone (90) gave 2-phenyl-3,4-dihydroquinoxaline (91) (LiAlH4, THF, N2, 0°C reflux, 24 h 65%). ... 

Cyanogen and ca-bromoacetophenone give di-imino-dihydroquimxaline and a phenyl-dihydroquinoxaline respectively. If the diketones are replaced by monocarbonyl compounds such as aldol, crotonie aldehyde, benzaldehyde, o- and p-anisaldehydes or iiiperonal, arsenated Schiff s bases result, e.g. 

The addition of cyanogen to 3 4-diaminophenylarsinic acid leads to the production of a di-imino-dikydroquinoxcdine (I), and the addition of w-bromoacetophenone leads to a phenyl-dihydroquinoxaline (II). No method has been found which will decide the position of the phenyl group in the quinoxaline ring. ... 

Methylquinoxaline with phenyUithium gave a separable mixture of 2-methyl-3-phenylquinoxaline (45), 2-methyl-3-phenyl-3,4-dihydroquinoxaline (46), and 2-methyl-2,3-diphenyl-1,2,3,4-tetrahydroquinoxaline (47) [PhLi (made in situ), Et20, <20°C, 90 min 20%, 45%, and 35%, respectively). 

A mixture of 2-methyl-3-methylene-7-nitro-4-phenyl-3,4-dihydroquinoxaline (97) and its quaternary perchlorate, 2,3-dimethyl-6-nitro-l-phenylquinoxali-nium perchlorate (98), underwent oxidative coupling to give l,2-bis(3-methyl-6-nitro-1 -phenyl-1,2-dihydroquinoxalin-2-ylidene)ethane (99) [Cu-(OAc)2, AcOH-MeCN, 95°C, 20 min 60%] many such condensations... 

Dimethyl-6-nitro-l-phenylquinoxalinium perchlorate (103) gave 2-methyl-3-methylene-7-nitro-l-phenyl-3,4-dihydroquinoxaline (104) (EtsN, AcMe,... 

Diphenylquinoxaline gave 2,3-diphenyl-l,2-dihydroquinoxaline (205) (TiCls, EtOH, 20°C, N2, 18 h 70%) and thence 2,3-diphenyl-l,2,3,4-tetra-hydroquinoxaline (206) (similar treatment 64%, as a mixture of cis- and frani-isomers) 1-benzyl-3-phenylquinoxalinium bromide (207) gave 1-benzyl-3-phenyl-l,2-dihydroquinoxaline (208) (TiCls, H2O, 20°C, 1 h 92%). ... 

Phenacyl-3-phenyl-l,2-dihydroquinoxaline (208) gave 2-phenylquinoxalme (HCl, MeOH, H2O, reflux, 15 min 53% acetophenone also isolated as its dinitrophenylhydrazone. Note that this is a passenger deacylation in the... 

Dimethylaminophenyl)-3,4-dihydroquinoxaline gave 2-(p-dimethylamino-phenyl)quinoxaline (tetrachlorobenzoquinone, PhH, reflux, 1 h 76%).780... 

Bromo-3-methyl-2-methylene-1 -phenyl-1,2-dihydroquinoxaline 2-Bromomethyl-6-methyl-3-... 

Methyl 6-methyl-2,3-dioxo-1,2,3,4-tetrahydro-5-quinoxalinecarboxylate 2-Methyl-3-methylene-7-methylsulfonyl-4-phenyl-3,4-dihydroquinoxaline 2-Methyl-3-methylene-7-nitro-4-phenyl-3,4-dihydroquinoxaline... 

Benzene-1,2-diamine undergoes reaction with halomethyl phenyl ketones to give 3-aryl-l,2-di-hydroquinoxalines 1, ° or after oxidation 2-arylquinoxalines 2. ° 1,2-Dihydroquinoxalines can be readily oxidized with different reagents. 

Catalytic reduction of 2-acetyl-3-methyl(or 3-phenyl)quinoxaline with 5% palladium on activated charcoal in ethanol gives 2-acetyl-3-methyl(or 3-phenyl)-l,4-dihydroquinoxaline. °... 

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