Upjohn dihydroxylation
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Upjohn dihydroxylation is an organic reaction converting an alkene to a cis vicinal diol, and was developed by V. VanRheenen, R. C. Kelly and D. Y. Cha of the Upjohn Company, USA in 1976.[1] It is a catalytic system using N-Methylmorpholine N-oxide (NMO) as stoichiometric re-oxidant for the Osmium tetroxide, and is superior to previous catalytic methods.
Prior to this method, use of stoichiometric amounts of the toxic and expensive osmium tetroxide was often necessary. The Upjohn dihydroxylation is still often used for the formation of cis-vicinal diols, however it can be slow and is prone to over-oxidation of the substrate to the vicinal di-ketone. One of the peculiarities of the dihydroxylation of olefins is that the standard "racemic" method (the Upjohn dihydroxyation) is slower and often lower yielding than the asymmetric method (the Sharpless asymmetric dihydroxylation).
[edit] Improvements to Upjohn Dihydroxylation
In response to these problems, Stuart Warren and co-workers[2] employed identical reaction conditions to the Sharpless asymmetric dihydroxylation, replacing the chiral ligands with the achiral Quinuclidine to give a racemic reaction product (assuming an achiral starting material is employed). This approach takes advantage of the fact that when using the Sharpless alkaloid ligands, the dihydroxylation of alkenes is faster and higher yielding than in their absence. This phenomenon became known as "ligand accelerated catalysis" a term coined by Barry Sharpless during the development of the asymmetric reaction.
[edit] References
- ^ V. VanRheenen, R. C. Kelly and D. Y. Cha Tetrahedron Lett. 1976, 1973-1976. (doi:10.1016/S0040-4039(00)78093-2)
- ^ J. Eames, H. Mitchell, A. Nelson, P. O’Brien, S. Warren, P. Wyatt, Perkin 1 1999, p1095 (doi:10.1039/a900277d)
