Imidazo quinoxalines preparation

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. 

Dimethyl-6-methylamino-5-quinoxalinamine (175) (prepared freshly as an ethanolic solution by catalytic hydrogenation of the corresponding nitro compound) and cyanogen bromide gave 3,4,8-trimethyl-3//-imidazo-[4,5-/]quinoxalin-2-amine (176) (20°C, 3.5 h 75%) the analogous... 

Some very clever syntheses of pyrazines were reported. Tandem Mn02-mediated oxidation followed by in situ trapping with aromatic or aliphatic 1,2-diamines was shown to give rise to quinoxalines, dihydropyrazines, pyrazines, and piperazines without the need to isolate highly reactive 1,2-dicarbonyl intermediates <03CC2286>. A new intramolecular cyclization route to highly substituted chiral 6,7-dihydro-5//-imidazo[l,5-a]pyrazin-8-ones like 157 from Meldrum s acid was developed <030L3907>, and 5-chloropyrido[3,4-6]pyrazines were prepared from 1,2-dicarbonyl compounds and 2-chloro-3,4-diaminopyridine <03H(60)925>. A synthesis of... 

The aromatic ring system has been prepared both from quinoxaline intermediates and from 1-phenylimidazoles. Reaction of the 2-chloroquinoxalines 1 with aminoacetaldehyde dimethylacetal followed by acid treatment of the resultant aminoacetals gave imidazo[l,2-ajquinoxaline (2) and its 4-phenyl derivative (3). Compound 3 was the... 

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. ... 

Dehydration of the aminobenzimidazoles 96 with polyphosphoric acid gave the cyclized products 97. ° Compound 98 has also been prepared by the same approach. Chloroethylbenzimidazoles such as 99 have been cyclized to imidazo[l,5,4-de]quinoxalines, ° and the bis(chloroethyl)-amine 101 was similarly cyclized to the quaternized heterocycle 102. ... 

A number of preparations of different types of imidazoquinoxalines were reported in 2013. Ma and coworkers devised an efficient one-pot synthesis of benzo[4,5]imidazo[l,2-a]quinoxalines via a copper-catalyzed process... 

As can be seen from the material presented in this review, imidazo[l,5-a]- and imidazo[l,2-a]quinoxalines arouse a great deal of interest of researchers owing to the wide range of biological activity exhibited by them. For this reason, in addition to the improvement of the known methods of their synthesis, an intensive search is carried out for new preparative procedures that afford diverse derivatives. 

Warner PL, Luber E (1980e) Process for preparing 4-substituted imidazo[l,2-a]quinoxalines. US Patent 4198508, 15 Apr 1980... 

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