Polymer-Supported Catalytic Asymmetric Sharpless Dihydroxylations of Olefins

The need for catalyst systems for the asymmetric dihydroxylation of olefins (AD) that combine the positive characteristics of the original homogeneous osmium catalysts with the ease of separation of heterogeneous catalysts led to the introduction of polymer-supported alkaloid ligands. Two major strategies for ligand recovery will be discussed here: (a) Attachment of the alkaloids to a solid support, such as an organic polymer or silica gel. After catalysis the ligands can easily be recycled by simple filtration. (b) The alkaloids are anchored to a polymeric unit which allows catalysis to be performed under homogeneous conditions. After the reaction is complete, the ligand is isolated by precipitation upon addition of solvent followed by filtration. Recent results of investigations of both strategies will be presented.