Polymer-bound diphenylphosphane hydrobromide, a mild acid for the activation of enol ethers:: Applications in polymer-assisted glycosidations

Polymer-bound diphenylphosphane hydrobromide 2 shows excellent properties in the activation of enol ethers and glycals, the introduction and cleavage of THP ethers being promoted with excellent yields with this functionalized polymer. Glycosidations of glycals work equally well, with suppression of the formation of undesired Ferrier rearranged products. The reagent is sufficiently mild to leave labile 2-deoxy glycosidic bonds and acid-labile protecting groups intact. It can be employed to transfer disaccharide glycosyl donors onto aglycons and is also selective for the promotion of two glycosidations in one pot. Highly hindered glycosyl donor groups such as the hydroxy group at C-13 of the baccatin III framework can be glycosylated with glycals in the presence of this polymer-bound reagent. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.