An improved practical Pd/C-catalyzed Sonogashira cross-coupling reaction for the synthesis of liquid crystals of trans-cyclohexyltolans

An improved practical synthesis of liquid crystals of trans‐cyclohexyltolans by Sonogashira cross‐coupling reaction of 1‐iodo‐4‐(trans‐4‐alkylcyclohexyl)benzene with aromatic terminal alkynes in the presence of Pd/C (palladium on activated carbon) as low as 0.03 mol% of Pd and CuI (2 mol%) in a mixture solvent of acetone–water (5:2 in volume) is described. The liquid crystals could be obtained in high yields as a solid with excellent purity by simple filtration, and the filtrate could be reused several times while still retaining high catalytic activity. Copyright © 2010 John Wiley & Sons, Ltd. Liquid crystals of trans‐cyclohexyltolans were synthesized in high yields by Sonogashira cross‐coupling reaction of 1‐iodo‐4‐(trans‐4‐alkylcyclohexyl)benzene with aromatic terminal alkynes in the presence of Pd/C as low as 0.03 mol% of Pd and CuI (2 mol%) in a mixture solvent of acetone–water (5:2 in volume).