Allyl acetates isomerization

As supporting evidence, rapid isomerization of the ds- and maui-Tr-allylpal-ladium complexes 27 and 28 is catalyzed by Pd(Ph3P)4 in THF even at -15 C to give a 45 55 equilibrium mixture from either 27 or 28[29-31].. Actually, in the intramolecular reaction of soft nucleophiles of 29 and 30, a trans-ds mi.xttire (31 and 32) (1 1) was obtained from /raiw-allylic acetate 29. On the... 

When the isomeric allylic acetates 11-A and 11-B react with dialkylcuprates, they give very similar product mixtures that contain mainly 11-C with a small amount of 11-D. Discuss the mechanistic implications of the formation of essentially the same product mixture from both reactants. 

It has been repored (86) that these same three isomeric aldehydes were formed from allyl acetate by a reaction catalyzed by rhodium trichloride and iron pentacarbonyl. Reaction proceeded at 135°C under 300 atm of H2/CO, but the product composition was not specified. 

The allylic acetate 47 can be isomerized to 48 by the palladium catalyst. When Pd(acac)2 and PPh3 were used, 47 was converted at 90°C for 12 hours into a 3.9 1 mixture of 47 and 48. But the ratio remained 17 1 when tris(o-methylphenyl)phosphite (52) was used. 

Unpublished work from our laboratory l2b) indicated that triethoxy-silane behaved differently than trichlorosilane. With linear olefins and chloroplatinic acid in a ratio of 1 5 x 10 3 it added much more slowly, did not isomerize the olefin, and formed secondary alkyltriethoxysilanes. However, it added rapidly to allyl acetate (see Table IV). 

The isomerization of allyl ethers and allyl acetals to vinyl ethers or vinyl acetals, respectively, has found many applications in organic synthesis (Equation (17)). Various transition metal catalysts have been reported in the literature for the isomerization of allyl ethers and allyl acetals. 

Desymmetrization of cyclic allyl acetals such as 2-substituted 4,7-hydrodioxepins or 5-methylene-1,3-dioxanes was investigated using ruthenium or nickel catalysts. The isomerization of the dioxanes was accomplished using Ru2Cl4(DIOP)/LiBHEt3 in high yield with up to 38% ee (Equation (22)).81... 

In 1996, Yamamoto et al. investigated the intramolecular Pd(0)-catalyzed reactions of allylic acetates with allenes and observed the isomerization of triene 261 to the cyclic diene 262 (Scheme 15.83) [156], The reaction probably proceeds via oxidative addition to Pd(0), insertion of the allene and return of the acetate. 

The reaction is believed to proceed via a c-allyl copper complex, in which the carbon-copper bond is formed at the "/-position, anti to the acetate leaving group. Reductive elimination of copper led to pure "/-substitution. With cyclic aliphatic allylic acetates, the selectivity is generally lower because the o-allyl copper complex can isomerize to the ir-allyl complex with loss of regioselectivity. 

The concept (see Scheme 15) was introduced by Shue et al.,144-85-861 who used a zinc-induced reductive isomerization of diasteromeric allylic bromides which already contained the R2 side chain. Because of the lack of stereocontrol at the a-carbon, and of difficulties in obtaining the allylic bromide, this method has not been further developed instead, homochiral allylic acetates or mesylates have been used. 

The most intense interest in the addition of oxygen nucleophiles to Tr-allylpalladium complexes has centered on the delivery of OAc. For example, in allylpalladium-OAc complexes, acetate can be induced to migrate to the allyl ligand by the addition of CO (equation 46).162-164 Rearrangements and isomerizations of allyl acetates can also be readily accomplished via Pd catalysis (equations 47 and... 

Industrial (BASF) syntheses of vitamin A and vitamin A aldehyde have been accomplished utilizing the aldehydes obtained from allyl acetate hydroformylation.22 Either aldehyde (10) or (11) reacts with the same phosphorus ylide to give vitamin A or retinal (Scheme 4). Hydroformylation of 3-methyl-2-butenyl acetate gives a high yield of 2-formyl-3-methylbutyl acetate. Elimination of acetic acid followed by isomerization provides trimethylacrylaldehyde, which is an intermediate in the synthesis of irones (Scheme 5). 

Allosedamine, via ring-closing diene metathesis, 11, 224-225 Allyamines, isomerization, 10, 71 Allyindation reactions, alkenes and alkynes, 9, 693 Allyl acetals... 

Goering, H. L. Tseng, C. C. Alkylation of allylic derivatives. 7. Stereochemistry of alkylation of the isomeric trans-a,y-methyl(phenyl)-allyl acetates with lithium dialkylcuprates and alkylcyanocuprates. J. Org. Chem. 1983, 48, 3986-3990. 

Potassium fluoride can also be used as a base in the Pd(0)-catalyzed reactions of 149 with allylic acetates, as shown in Scheme 33 (94MI1). Sinou and co-workers reported that the acetates of the isomeric geraniol, nerol, and linalool gave similar mixtures of final sulfides 150e (94MI1). 

Isomerization/cyclization of ct-dienyl-to-allyl acetates (carbonates). This Pd catalyst effects isomerization and cyclization of these substrates to vic-disubsti-... 

Isomerization and elimination ofallylic acetates, In the presence of this Pd(0) species, allylic acetates undergo stereochemical isomerization and, more slowly, elimination to dienes (equation I). The conversion to dienes is general and can be effected usually in high yield, particularly when triethylamine is added to react with the acetic acid formed. 

The isomerization of allylic acetates can be a problem during palladium-catalyzed alkylation of these substrates, but can be circumvented by use of the lactone of the corresponding hydroxy acid (equation 11),... 

A recent report described analogous palladium(0)-catalyzed cyclizations of allyl acetates containing a conjugated dienyl-enophile component. Thus heating trienes (236) with acetic acid and lithium or sodium acetate in acetonitrile under reflux furnished mixtures of trans and cis cyclization products (238) and (239). It appears that the cyclized allylpalladium species (237) is trapped by acetate (via reversal of the oxidative addition (I) (K), Scheme 36) which results in an overall isomerization (236) - (238) +... 

Table 16 Pd° Catalyzed Cyclizations via Isomerizations of a-Dienyl-

Ruthenium hydride-catalyzed carbon-carbon double bond migration is applicable to isomerization of allylic acetals and ketals 31 to vinylic ones 32, which undergo selective cross-aldol type reaction by treatment with Bp3-Et20 to yield 33 (Eq. 12.12) [18]. 

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). 

Intramolecular reactions of allylic acetates with conjugated dienes catalyzed by Pd(0) lead to a 1,4-addition of a carbon and an oxygen nucleophile to the diene. The reaction, which is formally an isomerization, involves tw different yr-allyl complexes (Scheme 8-4) [44]. Reaction of 22 in the presence of the Pd(0) catalyst Pd2(dba)3-CHCl3 (dba = dibenzyl-ideneacetone) and LiOAc/HOAc in acetonitrile at reflux produces the cyclized isomer 25 in 62% yield. The double bond was exclusively of E stereochemistry, while the ring stereochemistry was a mixture of cis and tram isomers. Oxidative addition of the Pd(0) to the allylic acetate gives the intermediate jr-allyl complex 23. Subsequent insertion of a diene double bond into the allyl-palladium bond produces another jr-allyl intermediate (24), which is subsequendy attacked by acetate to give the product 25. 

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