Claisen rearrangements, allyl vinyl ethers

The substrates for allyl vinyl Claisen rearrangements are conveniently obtained by transetherification of vinyl alkyl ethers with allylic alcohols. Typical examples of this rearrangement are represented in Scheme 2.155. The transformation of allyl vinyl ether 482 into aldehyde 483 illustrates the unique potential of the Claisen rearrangement as a method to prepare angularly substituted derivatives from readily available precursors such as 484, a goal hardly achievable by other routes. Products of this type are used as key intermediates in the syntheses of many natural compounds. ... 

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 reaction was achieved through transfer vinylation of 67 with 68 by action of the [IrCl(cod)]2 complex to afford allyl homoallyl ethers 69, followed by a Claisen rearrangement of the ether 70. The Claisen rearrangement of allyl homoallyl ethers to y,5-unsaturated aldehydes has been reported previously [6]. 

The procedure described illustrates a new general synthetic method for the preparation of (E)-3-allyloxyacryl ic acids and their conversion to a-unsubstituted y,5-unsaturated aldehydes by subsequent Claisen rearrangement-decarboxyl at ion. Such aldehydes are traditionally prepared by Claisen rearrangements of allyl vinyl ethers. Allyl vinyl ethers are typically prepared by either mercury-catalyzed vinyl ether exchange with allylic alcohols or acid-catalyzed vinylation of allylic alcohols with acetals. The basic conditions required for alkoxide addition to the betaine to produce carboxyvinyl allyl ethers, as described in this report, nicely complements these two methods. In addition, this Claisen rearrangement is an... 

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

A second general approach to allyl /(-lluorovinyl ether intermediates involves the reaction of a /J-fluoro alcoholate with an allylic halide. Claisen rearrangement then produces a-fluoro carbonyl compounds. Although the tremendous rate acceleration caused by a-fluoro substitution in the vinyl fragment is not present here, the rearrangements take place under synthetically useful conditions. 

Metal-catalyzed isomerization of unsymmetrical diallyl ethers is a unique route to synthesize allyl vinyl ethers for the Claisen rearrangement. In 1977, Reuter and Salomon reported that heating the diallyl ether 23 in the presence of a catalytic amount of tris(triphenylphosphine)ruthenium(II) dichloride resulted in the... 

Claisen rearrangement of allyl vinyl ethers. " Allyl vinyl ethers undergo Claisen rearrangement at 25° in CICHiCHiCl in the presence of 2 equiv. of (CjH liAlSQH, (prepared from triethylaluminum and thiophenol) or (C3H5)2AICI/P(CftH,),. 

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

The a-substituted 1-methyl allyl vinyl ether was shown to isomerize with a strong preference for the irons product (i.e., 95 % irons, 5 % cfe) . This corresponds to a conformational preference for equatorial methyl (as opposed to axial) in the chair transition state of about 2.4 kcal.mole . The identical value was calculated from the irons product preference in the allyl ester Claisen rearrangements (see a-methyl allyl acetate and a-trifluoromethyl allyl trifluoroacetate). 

Eilbracht et al. have developed rhodium- or ruthenium-catalyzed one-pot synthesis of cyclopentanones from allyl vinyl ether via tandem Claisen rearrangement and hydroacylation [109-111]. This protocol requires elevated temperature (140-220°C) and also requires alkyl or aryl substituents at the terminal position of the allylic double bond to prevent undesirable double bond migration in the intermediary formed, unsaturated aldehyde. 

The Claisen rearrangement can be catalyzed by Lewis acids, often with improved stereoselectivity. Acyclic allyl vinyl ethers give a Claisen rearrangement upon treatment with a catalytic amount of Pd(II). 5 a Ho(fod) catalyst has been used as well. An example of this type of reaction is the conversion of 592 to a 22 71 mixture of 593 and 594 in 99% yield. 47... 

A number of vinylation-Claisen rearrangements have been reported as a tandem reaction. Since no additional reagents are required in the thermal Claisen rearrangement, the allyl vinyl ethers can rearrange without isolation. No convenient introduction methods of basically reactive vinyl groups are available for the selective preparation of functionalized vinyl ethers [11,13,14, 22, 24]. 

Denmark SE, Harmata MA, White KS. Studies on the addition of allylc oxides to sulfonylations. Preparation of highly substituted allyl vinyl ethers for carhanionic Claisen rearrangements. 7. Org. Chem. 1987 52 4031-4042. 

A general advantage of this acetal, which undergoes hydrolysis at approximately 10 times the rate of THP, " is that it does not confer an additional diastereomeric center to the protected substrate. Access to allyl vinyl ethers for subsequent Claisen rearrangements " is illustrated in eq 2. 

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

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)... 

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