Allyl esters rearrangements

Allylic ester rearrangement is catalyzed by both Pd(II) and Pd(0) compounds, but their catalyses are different mechanistically. Allylic rearrangement of allylic acetates takes place by the use of Pd(OAc>2-Ph3P [Pd(0)-phosphine] as a catalyst[492,493]. An equilibrium mixture of 796 and 797 in a ratio of 1.9 1.0 was obtained[494]. The Pd(0)-Ph3P-catalyzed rearrangement is explained by rr-allylpalladium complex formation[495]. 

Asymmetric Ireland-Claisen Rearrangements. Chiral enolates derived from the boron complex (5) and allyl esters rearrange with excellent selectivity upon warming to —20 °C for a period of 1-2 weeks (eqs 9 and 10). As discussed above, the geometry of the intermediate enolate can be controlled by appropriate choice of base and solvent, thus allowing access to either syn or anti configuration in the product The reaction can be completed in 2-4 days with little erosion in selectivity when run at 4 °C. 

CUiisen rearrangement of aUyl esters. Ireland and Mueller report that lithium enulates of allyl esters rearrange rapidly at room temperature or slightly above to the corresponding v,2>-unsaturated acids. Thus the allyl ester (I) is converted into the lithium enolate (2) by treatment with lithium isopropylcyclohexylamide in THF at —78". The solution of (2) is then allowed to warm to 25° for 10 min. The y.( -unsaturated acid (3)... 

Allyl esters rearrange to isomeric allyl esters. Reactions are concerted and undoubtedly involve 6-center polar transition states, viz. 

Substituent effects in the allyl ester rearrangements are very similar to those observed in the ester reverse ene-type eliminations. This is apparent from the relative rate comparisons of Table 8. At the a- and y-carbons, reaction rates are observed to increase in the order CF3 < H < CH3. The rate accelerations by methyl substitution for hydrogen at the a-carbons are factors of 40 and 23, and at the y-carbon are factors of 55 and 23. These effects should be compared with the rate accelerations by methyl for hydrogen substitution at the a-carbon in the ester ene reactions, i.e., from Table 2, i-PrOAc/EtOAc = 18.7 and t-BuOAc/i-PrOAc = 53. One may conclude that the positive formal charge densities at the a- and... 

As in the allylic ester rearrangement, no dependence on the N-protecting group was observed and the syn-product was formed preferentially [85]. According to a suggestion of Hoppe [86], the syn/anti terminology [87] is used for the easy description of the allenic rearrangement products. 

Cartxjxylalion and subsequent allylation of alkyl heterocycles (via Claisen rearrangement of allyl esters)... 

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)... 

Allyl esters undergo rearrangement reactions at 300°C and above. Two examples are shown, one of which is degenerate, since the product and reactant are identical ... 

This effect is the basis of the synthetic importance of ester enolate Claisen rearrangements in which enolates or silyl enol ethers of allylic esters are rearranged into 4-pentenoate esters. 

An important variant is the rearrangement of silylketene acetals like 10 and 11 which are easily accessible from allyl esters 9. This so-called Ireland-Claisen rearrangement is a valuable carbon-carbon bond forming reaction that takes advantage of the fact that the reactants are first connected to each other by an ester linkage as in allyl esters 9, that are easy prepare. 

In summary, the evidence described above demonstrates three main mechanistic features of the rearrangement of allylic sulfenates to sulfoxides (1) spontaneous and wholly concerted [2,3]-sigmatropic shift of allyl or a-substituted allyl esters (7 a, b) at one extreme (2) complete stability of the y-aryl and y,y-dialkyl substituted allyl sulfenates as well as... 

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-... 

Enolates of allyl esters of a-amino acids are also subject to chelation-controlled Claisen rearrangement.249... 

Selenium dioxide is a useful reagent for allylic oxidation of alkenes. The products can include enones, allylic alcohols, or allylic esters, depending on the reaction conditions. The mechanism consists of three essential steps (a) an electrophilic ene reaction with Se02, (b) a [2,3]-sigmatropic rearrangement that restores the original location of the double bond, and (c) solvolysis of the resulting selenium ester.183... 

Morken et al. developed a reductive Claisen rearrangement of substituted allyl acrylates. The reaction of ( )-hex-2-enyl acrylate 175 was catalyzed by [Rh(COD)Cl]2 (0.25 mol %) and Me-DuPhos (0.5 mol %) with C MeSiH in benzene at 22 °C to give y,8-unsaturated ester 176 with high diastereoselect-ivity, 11 1 (Scheme 46) [80]. The reaction was carried out on a 10 g scale to provide a 70% yield of 176. This reaction was applied to allylic ester 177 to provide 178, which is a key intermediate in the total synthesis of inos-tamycin [24],... 

An allylic phosphorus ester rearrangement to form a new C-P bond has been reported under photochemical conditions.179 Under irradiation in the presence of 9,10-dicyanoanthracene, an allylic phosphite ester undergoes rearrangement to form the corresponding allyl-icphosphonite ester (Equation 4.40). Benzophenone serves only poorly as a photosensitizer in this reaction. 

Rearrangement of allyl trimethylsilyl ketene acetal, prepared by reaction of allylic ester enolates with trimethylsilyl chloride, to yield Y,5-unsaturated carboxylic a-cids. The Ireland-Claisen rearrangement seems to be advantageous to the other variants of the Claisen rearrangement in terms of E/Z geometry control and mild conditions. 

The Pd-catalyzed allylic alkylation of sulfinate ions, thiols, and thiocarboxylate ions with racemic cyclic and acyclic allylic esters in the presence of bisphosphane BPA generally provides for an efficient asymmetric synthesis of allylic sulfones, sulfides, and thioesters. The Pd-catalyzed rearrangements of allylic sulfinates and allylic O-thiocarbamates, both of which proceed very efficiently in the presence of BPA, are attractive alternative ways to the asymmetric synthesis of allylic sulfones and allyUc thioesters also starting from the corresponding racemic alcohols. 

The mechanism of the rearrangement catalyzed by Pd(II), typically by PdCN(RCN)2, is explained by the oxypalladation of an alkene to form 810 as an intermediate, or cyclization-induced rearrangement. As a limitation, no rearrangement takes place when the allylic ester 812 is substituted at the C-2 position of the allyl group, while a smooth rearrangement of 811 takes place[500]. 

Allylic esters of fluoroacetic acid were used in the Ireland silyl ketene acetal rearrangement procedures by the Welch group at Albany [164]. For example, Eq. (53) shows a highly diastereoselective rearrangement which formed an early stage in syntheses of 2,3-dideoxy-2-fluoro-3-C-methyl pentose nucleosides [165, 166]. If a stereoselective synthesis of a functionalised monofluorocompound is... 

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