Isomerization of an allylic ether

The only kinetic study of acid-catalyzed isomerization of a simple allylic ether was published by Braude and Gore who found that methyl a-phenylallyl ether isomerizes to methyl cinnamyl ether in anhydrous dioxane containing either boron trifluoride or hydrogen chloride. At 25°C, the ether is a quarter to an eighth as reactive as the corresponding alcohol. 

Alkene isomerizations involving homogeneous, catalyzed hydrogen migrations 

This section concerns alkene isomerizations in which hydrogen, rather than an anion or uncharged hydroxylic molecule, is the migrating entity. Only isomerizations involving migration of carbon-carbon double bonds under the influence of acidic, basic, or other catalysts in homogeneous systems are considered. 

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Allyl ethers may be removed by conversion to propenyl ethers, followed by acidic hydrolysis of the resulting enol ether. The isomerization of an allyl ether to... 

The isomerization of an allyl ether to a propenyl ether can be achieved either by treatment with potassium t-butoxide in dimethyl sulfoxide or by Wilkinson s catalyst, tris(triphenylphosphine)chlororhodium. ... 

The reaction is highly stereospecific and is always accompanied by inversion of the structure of the allyl group. This inversion is experimentally detectable when the a carbon or y carbon bears an alkyl substituent and is detectable in the case of allyl vinyl ether itself if the a or y carbons of the allyl group are labeled with (ref. 257). That the a carbon of the vinyl group of the ether becomes the carbonyl carbon of the product is demonstrated by the isomerization of isopropenyl allyl ether to hex-5-ene-2-one, and by the isomerization of CH2=CDOO H to CH2=CHCH2CH2CD02S7. 

Isomerization of allyl ethers. This complex (1), after exposure to hydrogen, is an effective catalyst for isomerization of primary allyl ethers of types 2 and 4 to rraws-propenyl ethers. Either THF or dioxane is a suitable solvent. 

The stereoselective isomerization of unsymmetrical diallyl ethers to allyl ( )-vinyl ethers was also carried out in the presence of a cationic iridium(l) catalyst. The catalyst prepared in situ by treating [Ir(cod)(PPh2Me)2]PF6 with hydrogen was found to be an excellent catalyst for the selective isomerization of a less substituted allyl group to an ( )-vinyl ether (Scheme 44).72... 

Similarly, the isomerization can be performed with an allylic ether [65, 76] and ketones such as 42 (with preservation of the double bond geometry ) [77] have also been reported to undergo these isomerizations (Scheme 1.17). 

Lead tetra-acetate oxidation of the allylic alcohols (170)—(172) and (182) leads to the formation of the epoxides (183)—(186), products of a novel internal addition reaction of the electron-deficient alcohol oxygen to the allylic double bond. In some cases, (171) and (172), the formation of a new type of acetoxylated enol ether (173) and (174) is observed. Oxidation of the allylic dienols (175) and (176) gives the epoxyacetates (187) and (188). A variety of cyclization products was also isolated. Their formation requires an isomerization of the allylic trans double bond to cis.69 Lead tetra-acetate oxidation of dihydro-y-ionol (189) gives the new bicyclic ether... 

The addition of an allyl alcohol to racemic allenyl sulfoxides results in vinyl ethers with the sulfinyl moiety at C-1 that undergo sigmatropic rearrangements upon distillation to produce 2,4-dienones after ehmination of sulfenic acid. In one example, an isomeric vinyl ether was obtained with a sulfinyl methyl substituent at C-2 that gave rise to a sulfinyl enone upon rearrangement [138]. In related work, the addition-elimination of an allyl alkoxide to a functionalized vinyl sulfoxide results in a sulfinyl enol ether that rearranges with loss of sulfenic acid to the unsaturated ester [139-141] (Scheme 21). 

As vinyl ethers were known to be poor substrates in Ru-catalyzed olefin metath-eses, it has been difficult to obtain cydic enol ethers by RCM of the vinyl ethers. Recently, a novel method to obtain cyclic enol ethers has been reported, which afforded cydic enol ethers directly from easily prepared dienes containing an allyl ether moiety [46]. Treatment of 70 with diene 99 in CH2CI2 in the presence of small amount of H2 resulted in a formation of dihydropyran 101 (Eq. 12.40). Treatment of 70 with H2 has been thought to produce an active catalyst for the olefin isomerization, and only metathesis products are formed until a small amount of H2 is introduced in the reaction. These results implied that this reaction most likely proceeded by way of a formation of the cyclic olefin 100, which was subsequently converted to dihydropyran 101 by the newly formed isomerization catalyst. In addition to the tandem reaction shown in Eq. 12.40, another method for obtaining cydic enol ethers from allyl ethers has also been demonstrated [46b]. This method induded addition of the hydride donor, such as NaBH4, to the reaction solution after the metathesis reaction had been completed. Although attempts to observe an active species for olefin isomerization in the presence H2 failed, these results suggested participation of hydride species in the olefin isomerization. 

Wilkinson s catalyst catalyzes the isomerization of an alkene to its thermodynamically most stable isomer. Isomerization of allyl ethers in this manner gives enol ethers, which can be hydrolyzed to give the free alcohol and a carbonyl compound. 

Isomerization. Cationic iridium complex effects selective isomerization of unsymmetrical diallyl ethers and conjugated boronates containing an allylic ether group, including an access to 7-(siloxy)allylboronic esters. The conversion of allyl homoallyl ethers to -y,8-unsaturated carbonyl compounds is promoted by [(cod)IrCl]2. 

Cleavage of allyl ethers (1, 300 2, 158 3, 246-247 5, 736). Allyl ethers are cleaved when heated at 60-80 with Pd on activated charcoal in the presence of an acid ( >-TsOH) to effect isomerization to an enol ether. ... 

For the isomerization of 2-propenyl ether the catalytic activity is in the order Ca0>La203, SrO, MgO>ZnO, AI2O3, SiOz —The initial isomerized product was exclusively cis form, indicating the intermediacy of an anionic allyl species as in the case of butene isomerization over solid bases. In the case of isomerization of 2-propenylamine, MgO and CaO were very active, while Z1O2 and ZnO were inac-tive. By the isomerization of., . -dimethyl-2-propenylamine, 100% cis-N,N- - TO-penylamine was initially formed, so that an anionic allyl intermediate was proposed. 

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