title: Twin-rotor system created on a [4]radialene frame.
abstract: [reaction: see text] Three extended [4]radialenes with two tricyclic rings connected with exocyclic butatriene units have been synthesized. The compounds, possessing thioxanthene and dihydroanthracene moieties as the terminal substituents, show a fast rotation around the butatriene bonds at ambient temperatures (DeltaG() = 13.7 and 14.9 kcal/mol, respectively). In contrast, the fluorene-substituted analogue shows a much higher rotational barrier (DeltaG() = 17.8 kcal/mol) of the butatriene bonds due to the reduced steric repulsion between the two fluorene moieties at the ground state.
authors.affiliation: Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Kuwatani
authors.forename: Gaku
authors.initials: G
authors.lastname: Yamamoto
authors.forename: Masahiko
authors.initials: M
authors.lastname: Iyoda