Synthesis of Ladder-Type π-Conjugated Heteroacenes via Palladium-Catalyzed Double N-Arylation and Intramolecular O-Arylation

Ladder-type heteroacenes containing pyrrole or furan rings, indolo[3,2-b]carbazoles and dibenzo[d,d‘]benzo[1,2-b:4,5-b‘]difurans, were effectively synthesized from the common intermediates, 2,5-bis(o-chloroaryl)hydroquinones. The key reactions are palladium-catalyzed double N-arylation of aniline and
intramolecular O-arylation, which enable regioselective ring closure. In addition to the parent indolo[3,2-b]carbazole and dibenzo[d,d‘]benzo[1,2-b:4,5-b‘]difuran, their derivatives with an alkyl or cyano
group were first synthesized. Photophysical and electrochemical studies showed that the obtained
heteroacenes have lower HOMO energy levels and larger band gaps than the corresponding hydrocarbon
acene, pentacene. An X-ray analysis of dibenzo[d,d‘]benzo[1,2-b:4,5-b‘]difuran revealed that it was packed
in herringbone fashion.