The ionic liquids [C4mim][PF6] and [C8mim][PF6] as cosolvents in asymmetric dihydroxylation give yields and enantioselectivity comparable or higher than those of the conventional H2O/tert-BuOH solvent system. After extraction of the reaction mixture with diethyl ether, the contamination of the product by osmium was remarkably low. The reuse of ionic liquid and catalyst is possible.
L. C. Branco, C. A. M. Afonso, J. Org. Chem., 2004, 69, 4381-4389.