Kinetics of Osmium Tetraoxide Catalyzed Trimethylamine N-Oxide Oxidations of Cyclohexene and α-Pinene to Diols

Article abstract of DOI:10.1021/jo00272a054

The kinetics of the osmium tetraoxide catalyzed oxidation of cyclohexene and of α-pinene with trimethylamine N-oxide in aqueous tert-butyl alcohol are first order in total osmium species, first order in trimethylamine N-oxide, and zero order in alkene but are strongly dependent on which alkene is used.Thus, the rate-determining step is attack of the trimethylamine N-oxide on the osmium(VI) ester, which is the major reservoir of osmium in the system.The reaction of cyclohexene is inhibited by pyridine with an inverse first-order dependence.Addition of α-pinene in slight excess of the osmium tetraoxide inhibits the oxidation of cyclohexene by more than 2 orders of magnitude, but additional α-pinene has no further effect.The oxidation of α-pinene is not inhibited by pyridine or cyclohexene.Oxidation of trans-stilbene in the presence of α-pinene results in slight (3percent) but mechanistically significant asymmetric induction.A side reaction in the dihydroxylation of α-pinene, overoxidation to α-hydroxy ketone, is suppressed by increasing the concentration of trimethylamine N-oxide.