1.4- dihydro-imidazo quinoxalines

An efficient approach to biologically relevant 1,4-dihydro-imidazo[4,5-b]quinoxalines 36 is described by Langer et al. employing a five-step anionic domino reaction of 3-aminoisoxazol 34 with bis(imi-doyDchlorides 35 in the presence of triethylamine in high yield (scheme 8).1191 Initially, the isoxazo[2,l-... 

Verma and collaborators reported selective syntheses of 4,5-dihydro-imidazo- and imidazo[l,5-a]quinoxalines via a modified Pictet-Spengler reaction by treating 2-imidazolyl anilines 134 with aromatic aldehydes in the presence ofp-toluenesulfonic acid in toluene (Scheme 66) (13TL5984). 

Amino-3-phenyl-3,4-dihydro-2(177)-quinoxalinone (181) and triphosgene gave 4-phenyl-47/-imidazo[l,5,4-< e]quinoxaline-2,5(l//, 6//)-dione (182) (EtsN, THF, 20°C, N2, until substrate gone by tic 65%) analogs Ukewise. ... 

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... 

Reduction of imidazo[l,2-a]quinoxaline with phosphorus and hydrogen iodide gives the 4,5-dihydro derivative 23. Under these conditions the 7-methoxy compound 24 is demethylated as well as reduced to give the hydroxy derivative 25. ... 

Imidazo[l,2-a]quinoxaline has been shown by two independent groups to have hypotensive activity in normal rats." 1,2-Dihydro derivatives of the ring system have been claimed as antiinflammatory agents and autonomic nerve blockers. The polyfluoro compound 18 is patented as a fungicide. ... 

A new and efficient anionic domino process of 3-aminoisoxazoles with oxaldiimidoyl dichlorides, involving cleavage of the isoxazole ring besides cyclisation reactions, provided a regioselective access to 2,4-dihydro-l//-imidazo[43-b)quinoxalines 33 <01EJO2257>. 

D. Catarzi, L. Cecchi, V. Colotta, G. Filacchioni, C. Martini, P. Tacchi, A. Lucacchini, Tricyclic heteroaromatic systems. Synthesis and A1 and A2a adenosine binding activities of some l-aryl-l,4 dihydro-3-methyl[l]benzop)frano[2,3-c]pyrazol-4-ones, l-aryl-4,9-dihydro-3-methyl-IH-pyrazolo [3,4-fc]quinolin-4-ones, and l-aryl-lH-imidazo[4,5-fc]quinoxalines, J. Med. Chem. 38 (1995) 1330-1336. 

---