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Sharpless asymmetric dihydroxylation
Sharpless asymmetric dihydroxylation (also called the Sharpless bishydroxylation) is the chemical reaction of an alkene with osmium tetroxide in the presence of a chiral quinine ligand to form a vicinal diol.
It is common practice to perform this reaction using a catalytic amount of osmium tetroxide, which after reaction is regenerated with either potassium ferricyanide or ''N''-methylmorpholine ''N''-oxide. This dramatically reduces the amount of the highly toxic and very expensive osmium tetroxide needed. These four reagents are commercially available premixed ("AD-mix"). The mixture containing (DHQ)2-PHAL is called AD-mix-α, and the mixture containing (DHQD)2-PHAL is called AD-mix-β.
Such chiral diols are important in organic synthesis. The introduction of chirality into nonchiral reactants through usage of a chiral catalysts is an important concept in organic synthesis. This reaction was developed principally by K. Barry Sharpless building on the already known racemic Upjohn dihydroxylation, for which he was awarded a share of the 2001 Nobel Prize in Chemistry.
== Background ==
Alkene dihydroxylation by Osmium tetroxide is an old and extremely useful method for the functionalization of olefins. However since osmium (VIII) is expensive and extremely toxic it became desirable to develop catalytic variants of this reaction. Some stoichiometric terminal oxidants that have been employed in these catalytic reactions include potassium chlorate, hydrogen peroxide (Milas hydroxylation), NMO (Upjohn dihydroxylation), tBHP (tert-butyl hydroperoxide), and potassium ferricyanide. K. Barry Sharpless was the first to develop a general, reliable enantioselective alkene dihydroxylation, referred to as the Sharpless Asymmetric Dihydroxylation (SAD). It still involves the use of low levels of OsO4 with a stoichiometric oxidant (K3Fe(CN)6), however it employs chiral nitrogenous ligands that create an asymmetric environment around the oxidant.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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