Allyl ethers rearrangement

For allyl ethers, rearrangement of the double bond to the more thermodynamically stable enol ether can be accomplished using trisjtriphenylphosphinejrho-dium(l) chloride (Wilkinson s catalyst). A possible mechanism for the rhodium(l)-... 

This procedure, when combined with the preparation of allyl ketals (p. 34), provides a general method for obtaining allyl substitution alpha to a carbonyl group. A discussion of some of these applications, as well as the vinyl allyl ether rearrangement which is involved, has been given by Hurd and Pollack. Also, the procedure can be repeated to allow the introduction of more than one allyl group. 

Such a cyclic mechanism was—in the opinion of these authors—quite similar to that proposed for (what they named) the Claisen allyl ether rearrangement (Scheme 25) ... 

Scheme 4 Transition states for lithiomethyl allyl ether rearrangements...

The Claisen-Johnson rearrangement [7] is closely related to both Saucy vinyl allyl ether rearrangement and Eschenmoser rearrangement. The reaction proceeds via a ketene acetal, which results from the condensation between an ortho-ester and an aUylic alcohol giving rise to a mixed orthoester followed by the elimination of the low-boihng-point alcohol. This ketene intermediate forms after rearrangement of a y,d-unsaturated ester (Scheme 6.1). 

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