Chemical and Electrochemical Asymmetric Dihydroxylation of Olefins in I₂-K₂CO₃-K₂OsO₂(OH)₄ and I₂-K₃PO₄/K₂HPO₄-K₂OsO₂(OH)₄ Systems with Sharpless' Ligand.

Torii, S.; Liu, P.; Bhuvaneswari, N.; Amatore, C.; Jutand, A. J. Org. Chem. 1996, 61, 3055.

Iodine-assisted chemical and electrochemical asymmetric dihydroxylation of various olefins in I₂-K₂CO₃-K₂OsO₂(OH)₄ and I₂-K₃PO₄/K₂HPO₄-K₂OsO₂(OH)₄ systems with Sharpless' ligand provided the optically active glycols in excellent conversion yields and high enantiomeric excesses. Iodine was used stoichiometrically for the chemical dihydroxylation and good results were obtained with non-conjugated olefins in contrast to the case of potassium ferricyanide as a co-oxidant. The potentiality of iodine as a co-oxidant under stoichiometric conditions has been proven to be effective as an oxidizing mediator in electrolysis systems. Iodine assisted asymmetric electro-dihydroxylation of olefins in either a t-BuOH/H₂O(1/1)-K₂CO₃/(DHQD)₂PHAL-(Pt) or t-BuOH/H₂O(1/1)-K₃PO₄/K₂HPO₄/(DHQD)₂PHAL-(Pt) system in the presence of potassium osmate in an undivided cell was investigated in detail. Irrespective of the substitution pattern, all the olefins afforded the diols in high yields and excellent enantiomeric excesses. A plausible mechanism is discussed on the basis of cyclic voltammograms as well as experimental observations.