Palladium‐Catalyzed Regioselective Cyclotrimerization of Acetylenes in Supercritical Carbon Dioxide

Abstract

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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Preparation of bio-polymeric materials, their microstructures and physical functionalities

“…[19][20][21][22] Segmented polyurethanes are elastomeric block copolymers that generally exhibit a phase-segregated morphology made up of soft rubbery segments and hard glassy or semi-crystalline segments. 23,24 The soft segment usually consists of polyether or polyester diols, whereas the hard segment consists of the diisocyanate component and a low molecular weight consists of the diisocyanate component and a low-molecular-weight chain extender. The advantage of segmented polyurethanes is that their segmental and domain structure can be controlled over a considerable range through the selection of the materials, their relative proportions, and the processing conditions.…”

“…Guo et al applied the epoxidation of the double bonds of fatty acids, followed by nucleophilic ring opening of the epoxide to make polyols for producing polyurethanes. [19][20][21][22][23] To further expand applications of the bio-based polymeric materials, previous studies were focusing on converting vegetable oils into useful PUs. Based on these studies, now it has become a main research field to functionalize vegetable oils by the introduction of aromatic co-monomers into the polymer structure, which could be suitable in the search for new viable polymeric materials.…”

Selective chemical reactions in supercritical carbon dioxide, water, and ionic liquids

“…These results were similar to those previously reported (35Á37). Besides coupling reactions (38Á41), there has been extensive research on other Pd-catalyzed chemical transformations such as cyclization (42,43), carbonylation (44Á46), etherification (47), oxidation (48,49), and polymerization (50Á52) in scCO 2 .…”

“…The reaction proceeds smoothly in neat water under basic conditions. The better solubility of the base (prolinol) in water increased the rate of the Green Chemistry Letters and Reviews 129 coupling reaction and afforded 76Á88% yield of the desired benzofurans (42). Various alkynes having non-protecting functional groups gave good yields of the desired product.…”

Formation and Catalytic Activity of Pd Nanoparticles on Silica in Supercritical CO2.

“…16,17 Recent examples include cyclotrimerization reactions and C-N bond formations. 18,19 More recently researchers have combined these areas of green chemistry and have performed reactions using heterogeneous catalysts in benign media. For example, ''solventless'' Suzuki coupling reactions have been conducted using palladium-doped potassium fluoride alumina, 20 Pd/C has been used as a recyclable catalyst in Suzuki cross-coupling reactions in water, 21 and polyurea-encapsulated Pd has been used in Heck,…”