A convenient synthesis of a 2,7-difunctional tetra(alkoxy)triphenylene involving 4,4-diacetoxy-3,3dialkoxybiphenyl as a key precursor and its conversion to extended hybrid mesogenic compounds

ANDRES ZELCER; FLORENCIA CECCHI; PABLO ALBORES; DANIEL GUILLON; HEINRICH BENOIT; DONNIO BETRAND; FABIO D. CUKIERNIK

LIQUID CRYSTALS

TAYLOR & FRANCIS LTD

Lugar: Londres; Año: 2013 p. 1121 - 1134

0267-8292

A new rational pathway to 2,7-difunctionalised-β-hexa-substituted triphenylenes is presented, requiring less protection/deprotection and purification steps than more conventional synthetic procedures in the framework of the ‘biphenyl route’. Main improvements are deprotection via alkaline hydrolysis of an ester in ethanol/water medium instead of using toxic and pyrophoric reagents like lithium diphenylphosphide, and the use of easily prepared brominated precursors instead of iodinated reagents for biphenyl synthesis. 4,4-Diacetoxy-3,3-bis(hexyloxy)biphenyl has been synthesised under this scheme, and characterised by proton nuclear magnetic resonance (1H NMR) spectrometry, elemental analysis and single-crystal crystallography. It crystallises in the P-1 space group, and exhibits a layered structure built-up through dipolar, C–H . . . π and C–H . . . O=C non-covalent interactions. This compound has been oxidatively coupled with 1,2-bis(hexyloxy)benzene to yield 2,7-dihydroxy-3,6,10,11-tetrakis(hexyloxy)triphenylene, a non-mesogen key precursor for the synthesis of the corresponding liquid-crystalline 2,7-difunctional triphenylenes. Indeed, a reactive 2,7-difunctional mesogen was prepared and used to produce new triphenylene-siloxane hybrid monomeric, trimeric and polymeric mesogens. All of them exhibited columnar hexagonal (Colh) mesophases.