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Antiaromatic 1,5‐Diaza‐ s ‐indacenes
Author(s) -
Hanida Kensuke,
Kim Jinseok,
Fukui Norihito,
Tsutsui Yusuke,
Seki Shu,
Kim Dongho,
Shinokubo Hiroshi
Publication year - 2021
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202109003
Subject(s) - antiaromaticity , chemistry , conjugated system , ring (chemistry) , aryl , photochemistry , palladium , crystallography , medicinal chemistry , stereochemistry , aromaticity , catalysis , organic chemistry , molecule , polymer , alkyl
s ‐Indacene is a classical non‐alternant hydrocarbon that contains 12 π‐electrons in a cyclic π‐conjugation system. Herein, we report its nitrogen‐doped analogue, 1,5‐diaza‐ s ‐indacene. 1,5‐Diaza‐ s ‐indacenes were readily prepared from commercially available 2,5‐dichlorobenzene‐1,4‐diamine through a two‐step transformation consisting of a palladium‐catalyzed Larock cyclization with diaryl acetylenes followed by hydrogen abstraction. The thus obtained 1,5‐diaza‐ s ‐indacenes exhibited distinct antiaromaticity, as manifested in clear bond‐length alternation, a forbidden HOMO–LUMO transition, and a paratropic ring current. As compared to the parent s ‐indacene, the 1,5‐diaza‐ s ‐indacenes showed higher electron‐accepting ability owing to the presence of imine‐type nitrogen atoms. The 1,5‐diaza‐ s ‐indacene core is effectively conjugated with the peripheral aryl groups, which enables fine‐tuning of the absorption spectra and redox properties. The two possible localized forms of 1,5‐diaza‐ s ‐indacene were compared in terms of their energetic aspects.