title: Facile Synthesis of Polycyclic Pentalenes with Enhanced Hückel Antiaromaticity.
abstract: Pentalenes represent highly reactive Hückel antiaromatics with 8π electrons. Usually, pentalenes are stabilized by incorporation of two benzene rings in a fused fashion. In dibenzo[a,e]pentalenes, however, the high aromaticity of the fused benzene rings compromises the inherent antiaromaticity of the pentalene core. Herein, we disclose that this forfeited antiaromaticity can be restored by fusing four additional aromatic rings onto the peripheral positions of dibenzo[a,e]pentalenes. Such polycyclic pentalenes were prepared by successive transannular cyclizations via in situ-generated tetrakisdehydro[16]annulenes. The thus obtained compounds showed intriguing properties, for example, characteristic absorptions in the visible-to-near-infrared (NIR) region and low reduction potentials. These results hence afford a design principle to produce highly antiaromatic yet stable pentalenes. The antiaromaticity of the pentalene core can be widely tuned via the degree of aromaticity of the peripherally fused rings.
authors.affiliation: Department of Chemistry, Graduate School of Science and Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
authors.forename: Hiroya
authors.initials: H
authors.lastname: Oshima
authors.affiliation: Department of Chemistry, Graduate School of Science and Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
authors.forename: Aiko
authors.initials: A
authors.lastname: Fukazawa
authors.affiliation: Department of Chemistry, Graduate School of Science and Integrated Research Consortium on Chemical Sciences (IRCCS), Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.|Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo, Chikusa, Nagoya, 464-8602, Japan.
authors.forename: Shigehiro
authors.initials: S
authors.lastname: Yamaguchi
keywords: antiaromaticity; dehydroannulenes; pentalenes; transannular cyclization; π-conjugation