title: Synthesis of ladder-type pi-conjugated heteroacenes via palladium-catalyzed double N-arylation and intramolecular O-arylation.
abstract: 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.
authors.affiliation: Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Keiko
authors.initials: K
authors.lastname: Kawaguchi
authors.forename: Koji
authors.initials: K
authors.lastname: Nakano
authors.forename: Kyoko
authors.initials: K
authors.lastname: Nozaki