Peterson olefination

The Peterson olefination (also Peterson reaction ) is a reaction of names of organic chemistry. An α - silylated carbanion is eliminated with a ketone (or aldehyde) to an alkene as a reaction product. The reaction can proceed here differently, depending on whether the reaction takes place acidic or basic.

Reaction mechanism

The Peterson olefination is an important reaction in synthetic organic chemistry, as diastereoselective cis -or trans- alkenes can be synthesized from β - hydroxysilanes with her. Processing of the β - hydroxysilane with acid gives the alkene a while working up of the same β - hydroxysilane gives the alkene with opposite stereochemistry with base.

Treatment of β - hydroxysilane with acid results in protonation of an anti- elimination.

• Basic elimination ( below):

The influence of the base on the β - hydroxysilane leads to a concerted syn elimination.

As early as the first step two different stereoisomers can arise, there are a total of four possible pathways:

Alkyl substituents

Carrying the α -silyl carbanion only alkyl-, hydrogen, or electron- donating substituents, the stereochemistry of the Peterson Olefination can be controlled since at a sufficiently low temperature, the elimination is so slow that the intermediate β - hydroxysilane can be isolated.

Once isolated, the diastereomeric β - hydroxysilanes are separated. One diastereomer is treated with acid, while the other is treated with base, which results in the diastereoselective production of cis -and trans- alkene.

Electron-withdrawing substituents

Does the α - silylated carbanion electron - withdrawing substituents, the β - hydroxysilane intermediate is too unstable to be isolated in order, it is immediately the alkene.