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 nu...