title: Stereoselective synthesis and physicochemical properties of liquid-crystal compounds possessing a trans-2,5-disubstituted tetrahydropyran ring with negative dielectric anisotropy.
abstract: Three stereoselective syntheses and the physicochemical properties of trans,trans-5-(4-ethoxy-2,3-difluorophenyl)-2-(4-propylcyclohexyl)tetrahydropyran, which is an important liquid-crystal compound with a large negative dielectric anisotropy (Δε=-7.3), are described. The key step in the construction of the trans-2,5-disubstituted tetrahydropyran ring in the first approach involved a benzylic cation mediated intramolecular olefin cyclization of a 2-allyloxy-1-arylethanol derivative. The second method included the Et2 Zn-induced 1,2-aryl shift of a bromohydrin obtained from a hetero-Diels-Alder reaction, followed by stereoselective bromination. The third approach utilized the hetero-Diels-Alder reaction of trans-4-propylcyclohexanecarboxaldehyde and a 2-aryl-3-(trimethylsilyl)oxy-1,3-butadiene, followed by stereoselective protonation. From results obtained by using a quantum chemical calculation method, the reason why the target compound shows a large negative Δε value is discussed.
authors.affiliation: Sagami Chemical Research Institute (SCRI), 2743-1 Hayakawa, Ayase, Kanagawa 252-1193 (Japan).
authors.forename: Keisuke
authors.initials: K
authors.lastname: Araki
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Ryoji
authors.initials: R
authors.lastname: Tanaka
authors.forename: Saori
authors.initials: S
authors.lastname: Tanaka
authors.forename: Makoto
authors.initials: M
authors.lastname: Ushioda
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Gotoh
authors.forename: Tetsu
authors.initials: T
authors.lastname: Yamakawa
authors.forename: Munenori
authors.initials: M
authors.lastname: Inoue
keywords: cyclization; density functional calculations; liquid crystals; structure-activity relationships; synthesis design