Claisen rearrangement

The Claisen rearrangement is a powerful carbon-carbon bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl vinyl ether will initiate a [3,3]-sigmatropic rearrangement to give a γ,δ-unsaturated carbonyl.



Discovered in 1912, the Claisen rearrangement is the first recorded example of a [3,3]-sigmatropic rearrangement.

Many reviews have been written.

Mechanism
The Claisen rearrangement (and its variants) are exothermic (about 84 kJ/mol), concerted pericyclic reactions which according to the Woodward-Hoffmann rules show a suprafacial reaction pathway.

There are substantial solvent effects in the Claisen reactions. More polar solvents tend to accelerate the reaction to a greater extent. Hydrogen-bonding solvents gave the highest rate constants. For example, ethanol/water solvent mixtures give rate constants 10-fold higher than sulfolane.[1][2]

Trivalent organoaluminium reagents, such as trimethylaluminium, have been shown to accelerate this reaction.

Aromatic Claisen rearrangement
The aromatic variation of the Claisen rearrangement is the [3,3]-sigmatropic rearrangement of an allyl phenyl ether to an intermediate which quickly tautomerizes to an ortho-substituted phenol.



Bellus-Claisen rearrangement
The Bellus-Claisen rearrangement is the reaction of allylic ethers, amines, and thioethers with ketenes to give γ,δ-unsaturated esters, amides, and thioesters.



Eschenmoser-Claisen rearrangement
The Eschenmoser-Claisen rearrangement proceeds from an allylic alcohol to a γ,δ-unsaturated amide, and was developed by Albert Eschenmoser in 1964.



Ireland-Claisen rearrangement
The Ireland-Claisen rearrangement is the reaction of an allylic acetate with strong base (such as Lithium diisopropylamide) to give a γ,δ-unsaturated carboxylic acid.



Johnson-Claisen rearrangement
The Johnson-Claisen rearrangement is the reaction of an allylic alcohol with trimethyl orthoacetate to give a γ,δ-unsaturated ester.



Aza-Claisen
An iminium can serve as one of the pi-bonded moieties in the rearrangement.



Chromium Oxidation
Chromium can oxidize allylic alcohols to alpha-beta unsaturated ketones on the opposite side of the unsaturated bond from the alcohol. This is via a concerted hetero-claisen reaction, although there are mechanistic differences since the chromium atom has access to d- shell orbitals which allow the reaction under a less constrained set of geometries.



Chen-Mapp Reaction
The Chen-Mapp reaction also known as the [3,3]-Phosphorimidate Rearrangement or Staudinger-Claisen Reaction installs a phosphite in the place of an alcohol and takes advantage of the Staudinger Ligation to convert this to an imine. The subsequent claisen is driven by the fact that a P=O double bond is more energetically favorable than a P=N double bond.



Overman rearrangement
The Overman rearrangement (named after Larry Overman) is a Claisen rearrangement of allylic trichloroacetimidates to allylic trichloroacetamides.



Zwitterionic Claisen rearrangement
Unlike typical Claisen rearrangements which require heating, zwitterionic Claisen rearrangements take place at or below room temperature. The acyl ammonium ions are highly selective for Z-enolates under mild conditions.



Claisen rearrangement in nature
The enzyme Chorismate mutase (EC 5.4.99.5) catalyzes the Claisen rearrangement of chorismate ion to prephenate ion, a key intermediate in the shikimic acid pathway (the biosynthetic pathway towards the synthesis of phenylalanine and tyrosine).