1.4- Diethyl-1,2,3,4-tetrahydroquinoxaline

Quinoxaline gave l,4-diethyl-l,2,3,4-tetrahydroquinoxaline by indirect reductive alkylation (AcOH, KBHai, <15°C, 1 h, then reflux, 6h 87% presumably by nuclear reduction, A-acylation, and further reduction of the acetyl groups ). ... 

Benzylamino)methyl-l,2,3,4-tetrahydroquinoxaline (189) and diethyl oxalate gave 2-benzyM,4a,5,6-tetrahydro-l//-pyrido[l,2-fl]quinoxaline-l,2(3//)-dione (190) (neat reactants, 95°C, 20 h 46%). ... 

Aminoquinoxaline reacts with hydroxylamine hydrochloride to give 2-(hydroxyimino)-l,2-dihydroquinoxaline (140), also formed by dehydrogenation of 2-(hydroxyimino)tetrahydroquinoxaline (32) with diethyl diazodicarboxylate.148... 

A novel method of pyrazine ring formation involves the electrolysis of an activated dialkene and is illustrated by the conversion of o-bis( 8-diethoxycarbonylvinylamino)benzene (26) to the tetrahydroquinoxaline 27. The latter compound decomposes on heating at about 160° to quinoxaline and diethyl malonate. ... 

Reduction of quinoxaline with potassium borohydride in acetic acid gives an excellent yield of l,4-diethyl-l,2,3,4-tetrahydroquinoxaline phthalazine reacts similarly, and other carboxylic acids can be used. ... 

Diethyl (7 ,/ )-oxirane-2,3-dicarboxylate was obtained from diethyl 2R, 31 )-(+)-tartrate with 1,2-DABs at elevated temperature under argon to give optically active tetrahydroquinoxalin-2-ones 473 in good yields (Scheme 2.99) (Woydowski et al. 1998). Note that for 1,2-DABs, and derivatives with electron-donating substituents, refluxing in ethanol is sufficient, whereas for 4-nitro-1,2-DAB, 155n, heating without a solvent at 155 °C is required (Woydowski et al. 1998). 

Scheme 2.99 Synthesis of optically active a-hydroxy-a-(tetrahydroquinoxalin-3-on-2-yl)esters 266 by ring transformation of diethyl (J ,/ )-oxirane-2,3-dicaiboxylate 4661...

Woo G, Snyder J, Wan Z (2002) Chapter 6.2 six-membered ring systems diazines and benzo derivatives. Prog Heterocycl Chem 14 279-309. doi 10.1016/S0959-6380(02)80015-0 Woydowski K, Ziemer B, Liebscher J (1998) Optically active a-hydroxy-a-(tetrahydroquinoxalin-3-on-2-yl)esters by ring transformation of (R,R)-diethyl oxirane-2,3-dicaiboxylate. Tetrahedron Asymm 9(7) 1231-1237. doi 10.1016/S0957-4166 (98)00097-4... 

The reaction of diethyl bromomalonate and 1,2-DABs gives tetrahydroquinoxalin-2-ones 27, which are then introduced into the aminoacylation reaction (Ahmad et al. 1964). On heating in 2 M HCl, carbamoyl derivatives 28 undergo intramolecular ami-dation to give imidazo[l,5-a]quinoxaline-l,3,4(277,377,57/)-triones 29 (Scheme 4.12) (Varano et al. 2001). 

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