Thermoregulated Copper-Free Sonogashira Coupling in Water

The Sonogashira cross-coupling reaction between aryl halides and terminal alkynes was carried out smoothly in water over a thermoregulated ligand-palladium catalyst under copper-free conditions, resulting in good to excellent yields. The Sonogashira reaction was sensitive to the electronic nature of the substituents on the aryl halides. Aryl halides with an electron-withdrawing group showed higher reactivity than those with an electron-donating group. Particularly, this protocol could be applied to the synthesis of liquid crystals involving trans-cyclohexyltolans. The products could be separated from the reaction system easily by decanting, and the catalyst was recovered in water and used directly for the next run.