Polystyrene-supported triphenylarsines useful ligands in palladium-catalyzed aryl halide homocoupling reactions and a catalyst for alkene epoxidation using hydrogen peroxide》.pdfVIP

Tetrahedron 61 (2005) 12053–12057 Polystyrene-supported triphenylarsines: useful ligands in palladium-catalyzed aryl halide homocoupling reactions and a catalyst for alkene epoxidation using hydrogen peroxide Helen Song He, Chuanxin Zhang, Chris Ka-Wo Ng and Patrick H. Toy* Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, People’s Republic of China Received 14 June 2005; revised 7 July 2005; accepted 7 July 2005 Available online 6 October 2005 Abstract—The utility of both soluble (non-cross-linked) and insoluble (cross-linked) polystyrene-supported triphenylarsine reagents were examined. These reagents were prepared by standard radical polymerization methodology and used in palladium-catalyzed homocoupling reactions of aryl halides. The insoluble reagent was also used as a catalyst precursor in heterogeneous alkene epoxidation reactions in which aqueous hydrogen peroxide was the stoichiometric oxidant. For the aryl halide homocoupling reactions, both reagents worked well and afforded similar results. Unhindered aryl iodides afforded the best yields in the shortest reaction times compared to aryl bromides. The epoxidation reactions of unfunctionalized alkenes were not very efficient. This was probably due to the hydrophobicity of the polystyrene matrix, which did not swell in the reaction medium. Thus, since a microporous, gel-type polystyrene matrix was used, the majority of the arsine groups were inaccessible to the reaction components and therefore incapable of participating in catalysis. q 2005 Elsevier Ltd. All rights reserved. 1. Introduction Triphenylarsine is an important reagent in organic synthesis