Scheme 4. Preparation of halohydrins from epoxides using polymer-supported halogen-triphenyl phosphine complexes.

Recently, a polymer-supported Pd-complex was described in which the metal is coordinated to a polymer-bound triphenylphosphine moiety [27]. This catalyst can be used for Suzuki couplings and other Pd-catalyzed C-C bond-forming reactions.

Polymer (PEG)-Supported Burgess Reagent

The cyclodehydration of N-(hydroxyethyl)-amides and -thioamides using Burgess reagent [28] is an important reaction for the preparation of oxazolines, thiazolines, oxazoles, and thi-azoles. However, the commercially available Burgess reagent is prone to oxidation and moisture and should thus be stored at low temperature; even then, it has only a very limited shelf-life. To overcome these problems the reagent was attached to a solid support [29], Coupling chlorosulfonyl isocycanate 23 to dry PEG monomethylether 24 (MW = 750) and then treating the polymer 27 with triethylamine produced the desired reagent 28 (Scheme 5). Cyclodehydration of, for example, threonine-derived amide 29 in hot dioxane/THF occurred cleanly and provided oxazoline 30 in 15 % higher yield than the standard Burgess reagent [29]. On completion of the reaction, the product was obtained cleanly by simple filtration through a short plug of silica to remove the polymer-bound reagent.

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