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K. Barry Sharpless was the first to develop a general, reliable enantioselective alkene dihydroxylation, referred to as the Sharpless asymmetric dihydroxylation (SAD). Low levels of OsO 4 are combined with a stoichiometric ferricyanide oxidant in the presence of chiral nitrogenous ligands to create an asymmetric environment around the oxidant.
Dihydroxylation is the process by which an alkene is converted into a vicinal diol. Although there are many routes to accomplish this oxidation , the most common and direct processes use a high-oxidation-state transition metal (typically osmium or manganese).
In organic chemistry, AD-mix is a commercially available mixture of reagents that acts as an asymmetric catalyst for various chemical reactions, including the Sharpless asymmetric dihydroxylation of alkenes. The two letters AD, stand for asymmetric dihydroxylation.
Enantioselective synthesis, also called asymmetric synthesis, [1] is a form of chemical synthesis. It is defined by IUPAC as "a chemical reaction (or reaction sequence) in which one or more new elements of chirality are formed in a substrate molecule and which produces the stereoisomeric ( enantiomeric or diastereomeric ) products in unequal ...
Lewis bases such as tertiary amines and pyridines increase the rate of dihydroxylation. This "ligand-acceleration" arises via the formation of adduct OsO 4 L, which adds more rapidly to the alkene. If the amine is chiral, then the dihydroxylation can proceed with enantioselectivity (see Sharpless asymmetric dihydroxylation). [14]
[1] [2] The cis-diol is formed by reaction of alkenes with hydrogen peroxide and either ultraviolet light or a catalytic osmium tetroxide, [3] vanadium pentoxide, or chromium trioxide. [4] The reaction has been superseded in synthetic chemistry by the Upjohn dihydroxylation and later by the Sharpless asymmetric dihydroxylation.
The Sharpless dihydroxylation is such a reaction: it converts alkenes into diols. The hydroxy groups are provided by hydrogen peroxide , which adds across the double bond of alkenes . [ 12 ]
The Upjohn dihydroxylation is an organic reaction which converts an alkene to a cis vicinal diol. It was developed by V. VanRheenen, R. C. Kelly and D. Y. Cha of the Upjohn Company in 1976. [1] It is a catalytic system using N-methylmorpholine N-oxide (NMO) as stoichiometric re-oxidant for the osmium tetroxide. It is superior to previous ...