Synthesis and Mesomorphic Properties of Liquid Crystals with 5-(4-Alkoxyphenylethynyl)tropolone.

New troponoid liquid crystals with 5-(4-alkoxyphenylethynyl)tropolone cores were synthesized. The 5-(4-alkoxyphenylethynyl)tropolones were obtained by the palladium-catalyzed cross-coupling of 5-iodotropolone with 4-alkoxyphenylacetylenes. The 2-alkoxy-5-(4-alkoxyphenylethynyl)tropones (1A) showed enantiotropic smectic phases, such as smectic A, C, and B. The 2-(4-alkoxy)benzoyloxy-5-(4-alkoxyphenylethynyl)tropones (1B) had enantiotropic nematic and smectic C phases. The 2-alkoxytropone derivatives (1A) had higher clearing temperatures and lower melting points than the corresponding benzene derivatives (2A). However, the 2-(4-alkoxybenzoyl)tropone derivatives (1B) had lower clearing temperatures and higher melting points than the corresponding benzene derivatives (2B).