Catalytic cycle asymmetric dihydroxylation reaction

Figure 2.9 Catalytic cycle for the asymmetric dihydroxylation reaction in two phases BUOH-H2O with K3pe(CN)5 as the stoichiometric reoxidant. The ligand is bound via tertiary nitrogen atom.

Scheme 14.8 Catalytic cycle of the asymmetric dihydroxylation reaction in two phases, with KalFeCNe] as the final oxidant...

Although a large number of asymmetric catalytic reactions with impressive catalytic activities and enantioselectivities have been reported, the mechanistic details at a molecular level have been firmly established for only a few. Asymmetric isomerization, hydrogenation, epoxidation, and alkene dihydroxylation are some of the reactions where the proposed catalytic cycles could be backed with kinetic, spectroscopic, and other evidence. In all these systems kinetic factors are responsible for the observed enantioselectivities. In other words, the rate of formation of one of the enantiomers of the organic product is much faster than that of its mirror image. 

The catalytic cycle for the asymmetric dihydroxylation is shown in Figure 20. The reaction is carried out in a 1/1 t-butanol/water mixture to solubilize the potassium ferricyanide/potassium carbonate used as the oxidant. The solvent mixture, normally miscible, separates into two liquid phases upon addition of the inorganic reagents. 

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