Sharpless bishydroxylation

Sharpless bishydroxylation or asymmetric dihydroxylation (AD) is a chemical reaction of an alkene with osmium tetroxide to form a diol (dialcohol). Chiral products can be formed by adding quinine derivatives. A more efficient way to perform this reaction is reoxidise the osmate, which is formed in the reaction, with potassium ferricyanide. This reduces the amount of the highly toxic and very expensive osmium tetroxide needed by up to 95%. It is possible to buy these mixtures as AD-mix α and AD-mix β.

Examples

The first step in the synthesis of azasugar 6 is a dihydroxylation reaction of the prochiral diene 1. Azasugars are pharmacologically relevant. The entire reaction sequence takes place in water as a reaction medium and protective groups were not required. Notice the chemoselectivity in the nucleophilic substitution of bromine by the hydroxyl group in step 2.

Related Topics:
Prochiral - Diene - Protective group - Chemoselectivity - Nucleophilic substitution

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