A Palladium-Catalyzed Glycosylation Reaction: The de Novo Synthesis of Natural and Unnatural Glycosides

Abstract

A highly stereoselective and sterospecific palladium-catalyzed glycosylation reaction of a variety of alcohols is reported. The reaction selectively converts α-2-substituted 6-carboxy-2H-pyran-3(6H)-ones into α-2-substituted 6-alkoxy-2H-pyran-3(6H)-ones with complete retention of configuration and similarly converts the pyranones with β-carboxy groups into pyranones with β-alkoxy groups. The reaction works equally well with both amino acid- and carbohydrate-based alcohols. To demonstrate the utility of this process for carbohydrate chemistry several of the products were selectively converted into α-manno-pyranosides in two additional steps. Because the 2-substituted 6-carboxy-2H-pyran-3(6H)-ones are prepared by asymmetric synthesis, this reaction can be used for the preparation of either d- or l-pyranones.