The Peterson olefination (also called the Peterson reaction) is the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

of α-silyl carbanions (1 in diagram below) with

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...

s (or

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

s) to form a β-hydroxysilane (2) which eliminates to form

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

s (3).

Several reviews have been published.Ager, D. J. ''Org. React.'' 1990, ''38'', 1.

Reaction mechanism

One attractive feature of the Peterson olefination is that it can be used to prepare either cis- or trans-alkenes from the same β-hydroxysilane. Treatment of the β-hydroxysilane with acid will yield one alkene, while treatment of the same β-hydroxysilane with base will yield the alkene of opposite stereochemistry.

Basic elimination

The action of base upon a β-hydroxysilane (1) results in a concerted ''syn'' elimination of (2) or (3) to form the desired alkene. The penta-coordinate

silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is al ...

intermediate (3) is postulated, but no proof exists to date. Peterson Basic Mechanism

Potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

alkoxides eliminate quickly, while

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

alkoxides generally require heating.

Magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...

alkoxides only eliminate in extreme conditions. The order of reactivity of alkoxides, K > Na >> Mg, is consistent with higher electron density on

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

, hence increasing the alkoxide nucleophilicity.

Acidic elimination

The treatment of the β-hydroxysilane (1) with acid results in protonation and an ''anti'' elimination to form the desired alkene. Peterson Acidic Mechanism

Alkyl substituents

When the α-silyl carbanion contains only

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl is derived from a cycloalk ...

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...

, or electron-donating substituents, the

stereochemical Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereois ...

outcome of the Peterson olefination can be controlled, because at low temperature the elimination is slow and 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, thus converted the material to an alkene with the required stereochemistry. Peterson Example Scheme

Electron-withdrawing substituents

When the α-silyl carbanion contains electron-withdrawing substituents, the Peterson olefination directly forms the alkene. The intermediate β-hydroxysilane cannot be isolated as it eliminates ''in-situ''. The basic elimination pathway has been postulated in these cases.

Variations

Acidic elimination conditions are sometimes not feasible as the acid also promotes double bond isomerization. Additionally, elimination using

potassium hydride Potassium hydride, KH, is the inorganic compound of potassium and hydrogen. It is an alkali metal hydride. It is a white solid, although commercial samples appear gray. It is a powerful superbase that is useful in organic synthesis. It is sold com ...

may not be feasible due to incompatible

functional group In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions regardless of the rest ...

s. Chan ''et al.'' have found that acylation of the intermediate silylcarbinol with either acetyl chloride or thionyl chloride gives a β-silyl

ester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ar ...

that will eliminate spontaneously at 25 °C giving the desired alkene. Corey and co-workers developed a method (sometimes dubbed the ''Corey-Peterson olefination'') using a silylated imine to yield an α,β-unsaturated aldehyde from a carbonyl compound in one step. For an example for its use in total synthesis see:

Kuwajima Taxol total synthesis The Kuwajima Taxol total synthesis by the group of Isao Kuwajima of the Tokyo Institute of Technology is one of several efforts in taxol total synthesis published in the 1990s. The total synthesis of Taxol is considered a landmark in organic synth ...

References

{{Alkenes Olefination reactions Carbon-carbon bond forming reactions Substitution reactions Name reactions