Allyl-Vinyl Ether Rearrangements

In addition to the classical allyl vinyl ether rearrangement, several variations have been developed which improve the synthetic value of the Claisen rearrangement with respect to the preparation of the parent compounds, reaction conditions and stereoselectivity. 

The different stereochemical course has been explained by unfavorable steric interactions of the methoxy group and the ring proton in the chair transition state B for the ortho ester variant resulting in a preference for the boatlike transition states C and D. On the other hand, chair transition state A predominates in the allyl vinyl ether rearrangement of 7 and 8. 

D.i. Allyl-Vinyl Ether Rearrangements. This reaction predated the Cope rearrangement and is obviously very similar. An alkenyl carbonyl product is obtained just as in the oxy-Cope rearrangement, but the carbonyl is generated directly rather than via initial enol formation. As with the Cope rearrangement, the... 

The Claisen-Johnson rearrangement is also a reaction of choice for the construction of quaternary centers in the synthesis of triquinanes and related ter-penes. Accordingly, transposition of aUyUc alcohol 125 is a cornerstone reaction in the synthesis of tricyclic compound 124, a key intermediate for the access to several triquinanes described by Iwata [28] (Scheme 6.17). Acid 126 was obtained in 57% yield after transposition and saponification. Claisen allyl vinyl ether rearrangement was also applied to allylic alcohol 125. Oxidation of the aldehyde inter-... 

Tsuji [69], in a stereoselective synthesis of de-AB-cholestan-9-one 315, studied an orthoester rearrangement followed by an allyl vinyl ether rearrangement affording the advanced intermediate 319 (Scheme 6.50). 

For related studies using the allyl vinyl ether rearrangement, see G. Rackur,... 

This chapter will discuss 1,3-dienes in a reaction with alkenes to give cyclohexene derivatives. This is a thermal reaction driven by interactions of molecular orbitals rather than ionic or polarized intermediates. In addition to the reaction of 1,3-dienes, 1,5-dienes undergo a rearrangement to a different 1,5-diene in what is known as a sigmatropic rearrangement. Similarly, allyl vinyl ethers rearrange to form alkenyl aldehydes or ketones. Both of these reactions tend to give difunctional molecules as products. 

The importance of the base used in the [2,3]-Wittig reaction is made clear by the work of Mitchell and coworkers who have reported the rearrangements of silyl- and stannyl-substituted diallyl ethers. They found that the use of LDA on such substrates (38, 41, 43) leads to [2,3]-Wittig reaction while employing lithium diethylamide can result in an allyl-vinyl ether rearrangement instead. 

The Claisen rearrangement is another important pericyclic reaction that is dramatically accelerated by aqueous solvents. The effect of solvation on this reaction has been studied extensively both experimentally and theoretically. For the allyl vinyl ether rearrangement (Scheme 6), Monte Carlo simulations have shown that both the number and the strength of solvent hydrogen bondings to the oxygen atom contribute to the rate acceleration of the reaction. Using the continuum AM1-SM2 solvation model, Cramer and Truhlar concluded... 

Claisen Rearrangements - allyl vinyl ether to an y,5-unsaturated carbonyl... 

CLAISEN - IRELAND Rearrangment Rearrangement ol allyl phenyl ethers to o (or p-)allylphenols or of allyl vinyl ethers to y.S-unsaturated aldehydes or ketones (Claisen) Rearrangement ol allyl esters as enolale anions to y.S-unsaturated acids (Ireland)... 

Rearrangement of allyl vinyl ethers or allyl aryl ethers... 

The Claisen rearrangemenC is a thermal rearrangement of allyl aryl ethers and allyl vinyl ethers respectively. It may be regarded as the oxa-version of the closely related Cope rearrangement. Claisen has discovered this reaction first on allyl vinyl ethers 1, and then extended to the rearrangement of allyl aryl ethers 2 to yield o-allylphenols 3 ... 

Two other important sigmatropic reactions are the Claisen rearrangement of an allyl aryl ether discussed in Section 18.4 and the Cope rearrangement of a 1,5-hexadiene. These two, along with the Diels-Alder reaction, are the most useful pericyclic reactions for organic synthesis many thousands of examples of all three are known. Note that the Claisen rearrangement occurs with both allylic aryl ethers and allylic vinylic ethers. 

Allyl vinyl ethers have been prepared using the ylide (101) but only from non-enolizable carbonyl compounds. The ethers rearrange on heating to give a-allyl aldehydes, e.g. (102). 

The reactants can be made from allylic alcohols by mercuric ion-catalyzed exchange with ethyl vinyl ether.220 The allyl vinyl ether need not be isolated and is often prepared under conditions that lead to its rearrangement. The simplest of all Claisen rearrangements, the conversion of allyl vinyl ether to 4-pentenal, typifies this process. 

Scheme 6.14. Claisen Rearrangements of Allyl Vinyl Ethers and Related... 

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