Palladium-catalyzed regioselective cyclotrimerization of acetylenes in supercritical carbon dioxide

The cyclotrimerization process of different substituted alkynes occurred smoothly in supercritical carbon dioxide for the first time. The reactions are catalyzed by palladium chloride. High yields and regioselectivities were observed when 2 equiv. of CuCl2 and 5 mL of MeOH were added. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).