Pushing steric bias in the Scholl reaction to access liquid crystalline crown ethers
Tobias Wöhrle1, Jochen Kirres, Martin Kaller
1Institut für Organische Chemie, Universität Stuttgart , 70569 Stuttgart, Germany.
Abstract:
Sterically congested o-terphenyl crown ethers with alkoxy substituents at the 2,3,4-position or 3,4,5-position were synthesized from the corresponding tetrabromodibenzo[15]crown-5 and the corresponding boronic acids or borolanes via Suzuki cross-coupling and subsequently cyclized to the corresponding triphenylenes utilizing the Scholl reaction. Both series of compounds were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction (SAXS, WAXS) regarding their mesomorphic properties. While all but one of the 3,4,5-substituted derivatives displayed liquid crystalline behavior (Col(h) and Col(r)), only the 2,3,4-substituted triphenylene with the shortest alkoxy chains was liquid crystalline (Col(r)).
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