Abstract
Substituted (E)‐2‐(ethynyl)but‐2‐ene and (E)‐hex‐3‐ene‐1,5‐diyne derivatives 6 and 10, respectively, were prepared by dicyclohexylcarbodiimide(DCC)‐mediated esterification of tris(dodecyloxy)benzoic acid (4) with (E)‐2‐[(triisopropylsilyl)ethynyl]but‐2‐ene‐1,4‐diol (3) and (E)‐2,3‐bis[(trimethylsilyl)ethynyl]but‐2‐ene‐1,4‐diol (8), respectively, followed by deprotection with Bu~4~NF in wet THF (Schemes 1 and 2). Oligomerization reactions of diyne derivative 10 were attempted by treatment with the Hay catalyst in the presence of mono‐alkyne 6 as an end‐capping reagent. Under these conditions, only compound 7 resulting from the homocoupling of 6 (Scheme 1), and polymers of 10 were obtained due to the difference in reactivity of the alkyne groups in 6 and 10. In contrast, when phenylacetylene was used as the stopper, the oligomerization of 10 afforded a mixture of end‐capped oligomers, from which 11–13 were isolated by column chromatography (Scheme 3). The poly(triacetylenes) (PTA) 16–18 were prepared in a similar manner starting from diol 8 and stearic acid (Schemes 4 and 5). Whereas the end‐capped monomers and dimers 11, 12, 16, and 17 with pendant long alkyl chains do not exhibit any liquid‐crystalline behavior, the trimeric derivatives 13 and 18 show mesomorphic properties, thus demonstrating that the poly(triacetylene) backbone can behave as a mesogenic unit.