Claisen Rearrangement

Abstract

Thermal isomerization of an allyl vinyl ether or of its nitrogen‐ or sulfur‐containing analogous derivatives to afford a bifunctionalized molecule in a [π2a + σ2s + π2s] process is known as the Claisen rearrangement. This reaction is a highly stereoselective [3,3]‐sigmatropic rearrangement of allyl vinyl or allyl aryl ethers to yield γ,δ‐unsaturated carbonyl compounds or o ‐allyl substituted phenols, respectively. In most cases, the reaction has been found to proceed preferably via a chair‐like transition state, and chiral, enantiomerically enriched starting materials give products of highly optical purity. This rearrangement is found to run faster in a polar solvent. The microwave irradiation can also accelerate the reaction rate. It is also found that substituents on allyl vinyl ether play important roles on the reactivity of corresponding allyl vinyl ethers and these modifications lead to more than 20 variations of the traditional Claisen rearrangement. This reaction, along with its various modifications, has wide applications in organic synthesis.