Claisen rearrangements, allyl vinyl

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

Methods of Preparation qfAllyl Vinyl Ethers 722J The Claisen Rearrangement 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. 

Thermal Claisen rearrangements of vinyl ethers of tertiary allylic alcohols (type C) give poor selectivities due to competition between transition states of more or less equal energy. 

The Claisen rearrangement of vinyl allyl ethers is a powerful reaction for the preparation of yS-unsaturated carbonyl compounds. The regioselectivity of the ketal version of this reaction has been studied, the results aiding the understanding and prediction of products formed from ketals of unsymmetrical ketones [equation (34)]. The allyl vinyl ether may also be formed by proto-... 

Conjugate addition of vinyllithium or a vinyl Grignard reagent to enones and subsequent oxidation afford the 1.4-diketone 16[25]. 4-Oxopentanals are synthesized from allylic alcohols by [3,3]sigmatropic rearrangement of their vinyl ethers and subsequent oxidation of the terminal double bond. Dihydrojasmone (18) was synthesized from allyl 2-octenyl ether (17) based on Claisen rearrangement and oxidation[25] (page 26). 

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)... 

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. 

It is possible to treat ketones with allyl alcohol and an acid catalyst to give y,5-unsaturated ketones directly, presumably by initial formation of the vinylic ethers, and then Claisen rearrangement.In an analogous procedure, the enolates (126) of allylic esters [formed by treatment of the esters with lithium isopropylcyclohex-... 

The basic pattern of the Claisen rearrangement is the conversion of a vinyl allyl ether to a y,8-enone. The reaction is also observed for allyl phenyl ethers, in which case the products are o-allylphenols. 

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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