Pushing Steric Bias in the Scholl Reaction to Access Liquid Crystalline Crown Ethers
journal contributionposted on 07.11.2014, 00:00 by Tobias Wöhrle, Jochen Kirres, Martin Kaller, Markus Mansueto, Stefan Tussetschläger, Sabine Laschat
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 tetrabromodibenzocrown-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 (Colh and Colr), only the 2,3,4-substititued triphenylene with the shortest alkoxy chains was liquid crystalline (Colr).