One-Pot Synthesis of 7‑(Benzimidazol-2-yl)thioxolumazine and -lumazine Derivatives via H2SO4‑Catalyzed Rearrangement of Quinoxalinones When Exposed to 5,6-Diamino-2-mercapto- and 2,5,6-Triaminopyrimidin-4-ols

A facile approach to a range of substituted 7-(benzimidazol-2-yl)­thioxolumazines [7-(benzimidazol-2-yl)-2-thioxo-2,3-dihydropteridin-4­(1H)-ones] and 7-(benzimidazol-2-yl)­lumazines [7-(benzimidazol-2-yl)­pteridine-2,4­(1H,3H)-diones] is described. These new biheterocyclic systems are obtained via H2SO4-catalyzed rearrangement of quinoxalin-2-ones in the presence of 5,6-diamino-2-mercapto- and 2,5,6-triaminopyrimidin-4-ols. Thus, benzimidazole and pteridine rings are constructed in one synthetic step. A plausible ANRORC (addition of nucleophile, ring opening and ring closure)-type reaction mechanism is proposed. Applying the rearrangement to the aza-analogue of 3-benzoylquinoxalin-2­(1H)-onei.e., 3-benzoylpyrido­[2,3-b]­pyrazin-2­(1H)-onewith 5,6-diamino-2-mercaptopyrimidin-4-ol makes it possible to synthesize inaccessible 7-(1H-imidazo­[4,5-b]­pyridin-2-yl)-6-phenyl-2-thioxo-2,3-dihydropteridin-4­(1H)-one. 7-(Benzimidazol-2-yl)-6-(2-fluorophenyl)-2-thioxo-2,3-dihydropteridin-4­(1H)-ones undergoes intramolecular nucleophilic substitution of fluorine by a nitrogen of the benzimidazole fragment with the formation of benzo­[4′,5′]­imidazo­[1′,2′:1,2]­quinolino­[4,3-g]­pteridine-2,4­(1H,3H)-diones as new heterocyclic systems.