Tungsten-mediated synthesis of triazafluorenes

Reaction of 2-pyridinecarboxaldehyde with aliphatic 1,2-diamines in aqueous/ethanolic solution mediated by [W(CN)4O2]4− affords the cationic disubstituted triazafluorenes in good yields. Single-crystal X-ray analysis of 4,9-bis(2-pyridyl)-4a,9a-dihydro-3H,9H-3,8a,9a-triazafluorenium hexafluorophosphate salt 1 reveals the formation of a novel heterocyclic tricycle. Plausible mechanism of triazafluorenes formation is discussed.