Polyazaacenes – On the Way to Stable, Fluorescent and Redox‐Active Derivatives

A new synthetic method for the preparation of polyazaacenes is described starting from two different nucleophilic building blocks. Disubstituted oxalic amidines 1 can be cyclized under mild conditions with 2,3‐dichloro‐5,6‐dicyanopyrazine ( 3 ) to yield 5,6‐dihydropyrazino[2,3‐ b ]pyrazines 4a – c . By employing higher temperatures and 2 equiv. of 3 , octaazanaphthacene 6 can be isolated. Similarly, pyrazino[2,3‐ b ]pyrazines 2 and bielectrophile 3 yielded novel dodecaazahexacenes 8 in addition to semicyclized derivative 9 . When tetraazafulvalene 10d was heated in the presence of an amine in xylene in the presence of oxygen, octaazahexacene 13 was isolated as the main product. Instead of pyrazino[2,3‐ b ]pyrazines 2 , this highly fluorescent polyazaacene was formed from a cascade reaction which involves a dyotropic rearrangement, an intramolecular Diels–Alder reaction and a multistep redox reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)