Tungsten-mediated synthesis of triazafluorenes

摘要

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, triaza analogue of fluorene. The identity and purity of the compounds have been verified with elemental analysis as well as IR, ~1H and ~(13)C NMR, UV-Vis, Raman and cyclic voltammetry measurements. Aliphatic 1,3- and 1,4-diamines as well as cycloali-phatic and aromatic ones are not reactive. The proposed pathway for the tungsten-mediated formation of triazafluorenes is discussed.