Ally 1 vinyl ethers, Claisen rearrangement

TaMe 9. Transition structure geometries, activation energies, and reaction energies for transition structures of Claisen rearrangement of ally vinyl ether... 

To exploit the whole capacity of the Claisen rearrangement, appropriate methods for the preparation of the ally vinyl ethers starting from ally] alcohols are necessary. The classical approach involves vinyl-ation with simple vinyl ethers or acetds. Unfortunately these methods fail with more complex systems and do not allow, except in the case of cyclic enol ethers, control of the stereochemistry of the substituted enol ether double bond. Until recently it was only possible to generate such substituted systems with appreciable stereocontrol via ketene 0-acetals. Their preparation by addition of allyl alcohols to substituted ynamines can lead to adducts of either ( )- or (Z)-geometry, depending upon the conditions used (Scheme 60). 

Ally lie ethers of enols (ally lie vinylic ethers) also undergo the Claisen rearrange-ment in fact, it was discovered with these compounds first ... 

Two other important sigmatropic reactions are the Cope rearrangement of a 1,5-hexadiene and the Claisen rearrangement of an ally aryl ether (Section 18.6). These two, along with the Diels-Aldor reaction, are the most useful pericyclic reactions for organic synthesis many thousands of examples of all three are known. Note that the Claisen rearrangement works well with both allyl aryl ethers and with allyl vinylic ethers. 

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