Sigmatropic rearrangements of allyl vinyl ethers

The [3, 3] sigmatropic rearrangement of allyl vinyl ethers is known as Claisen rearrangement. Allylic alcohols can be converted to allyl vinyl ethers by mercuric acetate catalysed exchange with ethyl vinyl ether. The allyl vinyl ether need not be isolated because it undergoes rearrangement to 4-pentenal. 

The thermal [3,3]-sigmatropic rearrangement of allyl vinyl ethers, first reported by Claisen in 1912, allows the preparation of y,6-unsaturated carbonyl compounds. This reaction is called [3,3]-sigmatropic rearrangement because the new a-bond has a 3,3 relationship to the former a-bond. The aromatic variant of the Claisen rearrangement, in which an aryl allyl ether (5) is converted thermally to the corresponding y,6-unsaturated carbonyl compound (6), is followed by a re-aromatization providing an ortho-di y phenol (7). 

The ability of charged substituents to accelerate the 3,3-sigmatropic rearrangement of allyl vinyl ethers (the Claisen rearrangement) has also been documented. The effect of oxyanion substituents on the rate and course of aliphatic Claisen rearrangements has been the subject of particular attention. - In 1972, Ireland and Mueller reported that the lithium enolate derivatives of allyl esters undergo rapid and effi-... 

Sigmatropic rearrangement of allyl vinyl ether substrates usually requires heating at around 200 . Allyl phenyl ether rearranges at room temperature in the presence of Lewis acid reagents, which have, however, turned out to be ineffective with aliphatic ethers. The concept of "combined acid-base attack previously mentioned (18,19) has motivated several successful experiments as shown in Schemes 10 through 12 (20). 

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