1,3-Diphenylbenzo[e][1,2,4]triazin-7(1H)-one, the oxidation product of 1,3-diphenyl-1,4-dihydro-1,2,4-benzotriazin-4-yl (Blatter's radical), reacts with N′-arylbenzamidines in PhMe at ca. 100 °C in the presence of N,N-diisopropylethylamine (Hünig's base) (1 equiv.) to give N′-aryl-N-(1,7-dihydro-7-oxo-1,3-diphenylbenzo[e][1,2,4]triazin-6-yl)benzimidamides in 49–95% yield. In neat AcOH heated at ca. 120 °C, N′–aryl-N-(1,7-dihydro-7-oxo-1,3-diphenylbenzo[e][1,2,4]triazin-6-yl)benzimidamides cyclodehydrate to give the novel 8-substituted 1,3,7-triphenyl-4,8-dihydro-1H-imidazo[4,5-g][1,2,4]benzotriazin-4-yls in 13–81% yield. During the optimization of this cyclodehydration an additional oxazole fused benzotriazinyl radical 1,3,7-triphenyl-1,4-dihydro[1,3]oxazolo[4,5-g][1,2,4]benzotriazin-4-yl was isolated as a side product and characterized. The CV and EPR data of the imidazolo- and oxazolo-fused radicals are presented as well as single crystal X-ray structures of 1,3,7-triphenyl-1,4-dihydro-[1,3]oxazolo[4,5-g][1,2,4]benzotriazin-4-yl and 1,3,7,8-tetraphenyl-4,8-dihydro-1H-imidazo[4,5-g][1,2,4]benzotriazin-4-yl.

This review article provides a perspective on the synthesis of alicyclic and heterocyclic ring-fused benzimidazoles, imidazo[4,5-f]benzimidazoles, and imidazo[5,4-f]benzimidazoles. These heterocycles have a plethora of biological activities with the iminoquinone and quinone derivatives displaying potent bioreductive antitumor activity. Synthesis is categorized according to the cyclization reaction and mechanisms are detailed. Nitrobenzene reduction, cyclization of aryl amidines, lactams and isothiocyanates are described. Protocols include condensation, cross-dehydrogenative coupling with transition metal catalysis, annulation onto benzimidazole, often using CuI-catalysis, and radical cyclization with homolytic aromatic substitution. Many oxidative transformations are under metal-free conditions, including using thermal, photochemical, and electrochemical methods. Syntheses of diazole analogues of mitomycin C derivatives are described. Traditional oxidations of o-(cycloamino)anilines using peroxides in acid via the t-amino effect remain popular.

2-Amino-N′-arylbenzamidines react with 4,5-dichloro-1,2,3-dithiazolium chloride (Appel salt) in the presence of Hünig’s base (2 equiv) to give in one step 3-aryl-4-imino-3,4-dihydroquinazoline-2-carbonitriles in 53–81% yields. Nine examples are presented along with the single-crystal X-ray structure of 4-imino-3-phenyl-3,4-dihydroquinazoline-2-carbonitrile. Furthermore, the behavior of the latter toward both acid and base hydrolysis is investigated. All new compounds are fully characterized, and a mechanistic rationale for the formation of the iminoquinazolines is provided.