Alkene dihydroxylation with OsO4 and NMO
Abstract
Alkene dihydroxylation using osmium(VIII) tetroxide (OsO4) as the oxidizing agent affords a vicinal diol. Because OsO4 is expensive, it is typically used in catalytic amounts, with N-methylmorpholine N-oxide (NMO) employed in stoechiometric amounts to regenerate the catalyst.
Keywords
Alkene, Osmium tetroxide, NMO, Diol
Category
Alkene
Mechanism
The reaction begins with the [3+2] cycloaddition performed between the alkene and the osmium(VIII) tetroxide , which leads to a five-membered cyclic osmate diester intermediate. A first nucleophilic addition of water at osmium occurs, after what a proton transfer step displaces one alkoxide arm, giving an osmium(VI) bound monoester bearing one free alcohol. This sequence is repeated to afford the desired cis-1,2-diol and the osmium(VI) hydrolyzed by-product. Finally, NMO reoxidizes this by-product back to osmium(VIII) tetroxide, leading to the catalyst regeneration.
Stereochemistry: Alkene dihydroxylation is a syn reaction, meaning a (E)-configured alkene leads to a trans diol and a (Z)-configuration gives a cis product.
Recent review
Tse, M. K.; Schröder, K.; Beller, M. Recent Developments in Metal‐Catalyzed Dihydroxylation of Alkenes. Modern Oxidation Methods. 2010, 1-36.