Immobilization of osmium catalysts for asymmetric dihydroxylation of olefins

Osmium-catalyzed asymmetric dihydroxylation provides powerful synthetic routes to optically active vicinal diols from olefins with high enantioselectivity. High catalytic efficiency using only 0.2-1.0 mol % of the osmium catalyst has been attained, and the chiral ligand may be recoverable in large-scale synthesis by extraction with dilute sulfuric acid. However, in spite of the significant advances in this transformation, high toxicity and volatility of the osmium components as well as possible contamination of toxic osmium species in the products have been obstacles for industrial applications. To address this issue, considerable efforts have been devoted to immobilization of the osmium catalyst. This review summarizes several promising methods for immobilization of the osmium components, especially focusing on solid phase-supported osmium catalysts for asymmetric dihydroxylation. 1 Introduction 2 Microencapsulation 3 Immobilization by Ionic Interaction 4 Immobilization on Supports Bearing Olefins 5 Miscellaneous Approaches 6 Perspectives