Synthesis of a Tetrabenzotetraaza[8]circulene by a "Fold-In" Oxidative Fusion Reaction

Fengkun Chen; Yong Seok Hong; Soji Shimizu; Dongho Kim; Takayuki Tanaka; Atsuhiro Osuka

doi:10.1002/anie.201505124

Synthesis of a Tetrabenzotetraaza[8]circulene by a "Fold-In" Oxidative Fusion Reaction

Angew Chem Int Ed Engl. 2015 Sep 1;54(36):10639-42. doi: 10.1002/anie.201505124. Epub 2015 Jul 15.

Authors

Fengkun Chen¹, Yong Seok Hong², Soji Shimizu³, Dongho Kim⁴, Takayuki Tanaka⁵, Atsuhiro Osuka⁶

Affiliations

¹ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan).
² Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 120-749 (Korea).
³ Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, Fukuoka 819-0395 (Japan).
⁴ Spectroscopy Laboratory for Functional π-Electronic Systems and Department of Chemistry, Yonsei University, Seoul 120-749 (Korea). dongho@yonsei.ac.kr.
⁵ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan). taka@kuchem.kyoto-u.ac.jp.
⁶ Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 (Japan). osuka@kuchem.kyoto-u.ac.jp.

PMID: 26216171
DOI: 10.1002/anie.201505124

Abstract

Tetrabenzotetraaza[8]circulene (1) has been synthesized in good yield by a "fold-in" oxidative fusion reaction of a 1,2-phenylene-bridged cyclic tetrapyrrole. X-ray diffraction analysis of 1 has revealed a planar square structure with a central cyclooctatetraene (COT) core that shows little alternation of the bond lengths. Despite these structural features, 1 shows aromatic-like character, such as sharp absorption bands, high fluorescence quantum yields (Φ(F)=0.55 in THF), and a single exponential fluorescence decay with τ(F)=3.8 ns. These observations indicate a dominant contribution of an [8]radialene-like π conjugation and hence aromatic character of the local aromatic segments in 1.

Keywords: aromaticity; circulenes; cyclooctatetraene; fused-ring systems; pyrroles.