2.3- Diaminoquinoxalines preparation

The curiously named fluorubine, 6,13-dihydropyrazino[2,3-f> 5,6-6 ]diquinoxaline (83), is a bright yellow compound prepared by condensation at 270 °C of 2,3-diaminoquinoxaline with 2,3-dichloroquinoxaline (03CB4039). The condensation can also be effected in dimethyl-formamide alternatively 2-amino-3-chloroquinoxaline will undergo self-condensation in the same solvent (63GEP1142981). 

A number of 2,3-diaminoquinoxalines have been prepared by heating a... 

Diaminoquinoxalines are obtained from the reaction of o-phenylenediamines with cyanogen in methanol containing a little aqueous sodium hydroxide solution." A variant on this procedure is first to prepare the oxaldiimido ester 7 from cyanogen and methanolic sodium methoxide and then to react the isolated ester with an o-phenylene-diamine (Scheme 5). " The latter method has been used with a wide range of nuclear-substituted diamines. 

Monoacylation of 2,3-diaminoquinoxalines has been achieved by reaction with an acid anhydride in THF. Under more vigorous conditions reaction of 2,3-diaminoquinoxalines with acid anhydrides results in ring closure to an imidazo[ ]quinoxaline. Similar ring closures have been carried out with aldehydes, acyl halides, formic acid, orthoesters, and urea. Polycyclic compounds have also been prepared from 2,3-diaminoquinoxaline by reaction with 1,-2-dicarbonyl compounds and 1,2-diamines, as illustrated in Scheme 7. 

Imidazo[4,5-h]quinoxalines have invariably been prepared from quinoxaline intermediates. Almost twenty years elapsed between the first reported synthesis of the ring system and the next publication containing an extensive study of the utility of reagents for converting 2,3-diaminoquinoxalines into 2-substituted imidazo[4,5-h]quinoxalines. ... 

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