Cascade Synthesis of Benzotriazulene with Three Embedded Azulene Units and Large Stokes Shifts

We report here the one‐pot synthesis of benzo[1,2‐a : 3,4‐a′ : 5,6‐a′′]triazulene (BTA), wherein three azulene units are embedded through a tandem reaction comprising two steps, Suzuki coupling and Knoevenagel condensation, between a readily available triborylated truxene precursor and 8‐bromo‐1‐nap...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2023-06, Vol.62 (25), p.e202218839-n/a
Main Authors: Liang, Yimin, Wang, Shangshang, Tang, Min, Wu, Lin, Bian, Lifang, Jiang, Liang, Tang, Zheng‐Bin, Liu, Jiali, Guan, Aocong, Liu, Zhichang
Format: Article
Language:English
Subjects:
Annulation
Azulene
Cascade chemical reactions
Condensates
Crystallography
Dimers
Fluorescence
Nitration
Nitrogen dioxide
Polycyclic Aromatic Hydrocarbons
Structure Elucidation
Superstructures
Synthesis
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Summary:We report here the one‐pot synthesis of benzo[1,2‐a : 3,4‐a′ : 5,6‐a′′]triazulene (BTA), wherein three azulene units are embedded through a tandem reaction comprising two steps, Suzuki coupling and Knoevenagel condensation, between a readily available triborylated truxene precursor and 8‐bromo‐1‐naphthaldehyde. Its nitration leads to a regioselective trinitrated product, namely, BTA‐NO2. Single‐crystal X‐ray crystallography revealed that the superstructure of BTA consists of a dimer stacked by two enantiomeric helicene conformers, while that of BTA‐NO2 consists of an unprecedented π‐tetramer stacked from two enantiomeric dimers, that is, four distinct helicene conformers. Both compounds show excellent stability and fluorescence with large Stokes shifts of up to 5100 cm−1. In addition, BTA‐NO2 exhibits a unique solvatochromic effect in different solvents and hydrogen‐bonding‐induced emission transfer in different ratios of THF/H2O solutions. A C3‐symmetrical truxene‐based benzotriazulene derivative with three embedded azulene units was concisely synthesized by means of a cascade [4+3] annulation involving a Suzuki coupling followed by Knoevenagel condensation of a readily available triborylated truxene precursor and 8‐bromo‐1‐naphthaldehyde. The regioselectively trinitrated product exhibits a large Stokes shift of up to 5100 cm−1 along with unique solvatochromic effects in different solvents.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202218839