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Chemical transformations of push–pull fluorenones: push–pull dibenzodicyanofulvenes as well as fluorenone– and dibenzodicyanofulvene–tetracyanobutadiene conjugates

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Abstract

Push–pull fluorenones (FOs) were synthesized by treating a benzopentalenequinone (BPO) derivative with alkynes that bear an electron-rich aniline moiety via a regioselective [4 + 2] cycloaddition (CA) followed by a [4 + 1] retrocycloaddition (RCA). The resulting FOs were readily converted into dibenzodicyanofulvenes (DBDCFs) by treatment with malononitrile in the presence of TiCl4 and pyridine. The FOs and DBDCFs exhibit intramolecular charge-transfer (ICT) that manifests in absorptions at 350–650 nm and amphoteric electrochemical behavior. Furthermore, FOs and DBDCFs that contain a C[triple bond, length as m-dash]C bond react with tetracyanoethylene in a formal [2 + 2] CA followed by a retro-electrocyclization to afford sterically congested tetracyanobutadiene (TCBD) conjugates. The substituent (H or Me) on the aromatic ring adjacent to the butadiene moiety thereby determines whether the butadiene adopts an s-cis or s-trans conformation, and thus controls the physicochemical properties of the resulting TCBDs. The TCBD conjugates exhibit ICT absorptions (≤800 nm) together with up to four reversible reduction steps.

Graphical abstract: Chemical transformations of push–pull fluorenones: push–pull dibenzodicyanofulvenes as well as fluorenone– and dibenzodicyanofulvene–tetracyanobutadiene conjugates

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Article information


Submitted
20 Dec 2019
Accepted
07 Mar 2020
First published
11 Mar 2020

Org. Biomol. Chem., 2020, Advance Article
Article type
Paper

Chemical transformations of push–pull fluorenones: push–pull dibenzodicyanofulvenes as well as fluorenone– and dibenzodicyanofulvene–tetracyanobutadiene conjugates

S. Kato, T. Kijima, Y. Shiota, T. Abe, S. Kuwako, H. Miyauchi, N. Yoshikawa, K. Yamamoto, K. Yoshizawa, T. Yoshihara, S. Tobita and Y. Nakamura, Org. Biomol. Chem., 2020, Advance Article , DOI: 10.1039/C9OB02706H

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