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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Protonation-Induced Antiaromaticity in Octaaza[8]circulenes: Cyclooctatetraene Scaffolds Constrained with Four
Shuhei Akahori1, Atsushi Kaga2, Jinseok Kim3
1Department of Molecular and Macromolecular Chemistry, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan.
Abstract:
The switching of cyclic π-conjugation pathways using external stimuli is an attractive research topic in the field of organic chemistry. Here, we synthesized C4h -symmetric octaaza[8]circulenes with four peripherally arranged amidine moieties that exhibit enhanced antiaromaticity upon protonation. Titration experiments with methanesulfonic acid revealed the formation of the tetraprotonated forms of the octaaza[8]circulenes in solution. Single-crystal X-ray diffraction analyses and theoretical calculations indicated that the contribution of the 8π antiaromatic character of the octaaza[8]circulenes is enhanced by the delocalization of charge through the protonation of the pyridine rings.
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