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.