Allenes allyl acetate

An allene moiety can serve as a nucleophile vis-a-vis a 7r-allylpalladium species generated from an allylic acetate moiety in substrates such as 495 (Scheme 124). The cyclization involving these two moieties generates another 7r-allyl intermediate, and the stage is set for the subsequent carbonylative cascade process as demonstrated by the transformation of 495 to 496.402... 

Allylphosphonium salts are synthesized by substitution of allyl halides with PPh3. The use of allyl alcohol, allyl acetate, or nitropropene with a palladium catalyst has also been reported.19 It is shown in this study that the organophosphorous compounds can be obtained by a palladium-catalyzed addition to an allene. A notable aspect of this method is that it can control the stereochemistry of the phosphonium salt, and that (Z)-allylphosphonium salts have been obtained in pure form for the first time. 

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 first step of the Pd-catalyzed reaction of allyl acetate bearing allene moiety 284 is attack of the 7i-allyl group at the central carbon of the allene to form 285, (or insertion of one of the allene double bonds) which is the 7r-allylpalladium 286. Then domino insertions of double bond, CO, double bond, CO and double bond occur to form six C—C bonds, affording 287. Finally, the tetracyclic diketone 288 was obtained by -elimination in 22% total yield [127],... 

Descoins et al. have found that the reaction of some dialkylcuprates with 3-acetoxypent-l-en-4-yne gives an allene as the major product 98). Propargylic acetates are more reactive than the allylic acetates towards dialkylcuprates. With a carboxymethyl substituent on the... 

The reaction is very sensitive to metal ion catalysis, particularly by Cu " and Ag", and oxygen inhibits the reaction. Po and Allen studied the uncatalysed reaction in oxygen-free solutions containing 10 M EDTA to ensure that the concentrations of free metal ions were insignificant. Under these conditions the reaction is first order with respect to peroxodisulphate and the rate is essentially independent of oxalate concentration (there is a slight increase in the first-order rate coefficient with increase of oxalate concentration). Allyl acetate inhibits the reaction and reduces the rate to that observed in the absence of oxalate. In the range pH 0.5-10.3 a rate maximum occurs at pH 4.5. The first-order rate coefficient for the reaction using 0.08 M disodium oxalate is expressed by... 

Allene carboxylic acids have been cyclized to butenolides with copper(II) chloride. Allene esters were converted to butenolides by treatment with acetic acid and LiBr. Cyclic carbonates can be prepared from allene alcohols using carbon dioxide and a palladium catalyst, and the reaction was accompanied by ary-lation when iodobenzene was added. Diene carboxylic acids have been cyclized using acetic acid and a palladium catalyst to form lactones that have an allylic acetate elsewhere in the molecule. With ketenes, carboxylic acids give anhydrides and acetic anhydride is prepared industrially in this manner [CH2=C=0 + MeC02H (MeC=0)20]. 

The first example of the use of enzyme and metal combinations to provide a dynamic resolution procedure was reported by Allen and Williams in 1996[18. In this case, a palladium (II) catalyst was employed that was able to racemize the allylic acetate substrate, but did not erode the enantioselectivity of the product allylic alcohol (Fig. 9-11). For example, a cyclic acetate was shown to undergo a simple kinetic resolution, affording enantiomerically enriched starting material and product at approximately 50 % conversion. However, performing the reaction in the presence of a palladium (II) catalyst facilitated a dynamic resolution by continuously racemiz-ing the starting material as the reaction progressed. 

Intramolecular reaction initiated by ionization of an allylic acetate and participated in by a distal allene linkage can have different ramifications when the molecule is also equipped with another double bond. The separation between this latter double bond and the allene moiety determines the structure of the final product. 

The two double bonds in 2,3-dimethoxycarbonyInorbomadiene are almost equally active. Furthermore, the reactions with methylenecyclopropane are stereoselective leading exclusively to the exo-isomers. Both observations are in striking contrast to the results obtained in the Pd(0) catalyzed cycloadditions of 2-[(tri-methylsilyl)methyl]allyl acetate with norbornadiene derivatives The last observations automatically lead to the conclusion that non-activated alkenes also could undergo these reactions. Indeed it was found that ethylene, norbornene, norbornadiene and allene react with methylenecyclopropane to give cycloadducts (Scheme 7). The reason for the limitation to these alkenes lies in the ability of methylenecyclopropane to compete successfully with alkenes in n-complexation to the metal. Thus cyclodimerization of methylenecyclopropane is much faster than codimerization with other alkenes, which give less stable rt-com-plexes with Pd(0). 

Allenes, 57, 285, 286, 356 Allcnic aldehydes, 189-190 Allenic amides, 169 AUenic boranes, 285, 286 Allenic esters, 301 Allenic ethers, 320 Allenic ketones, 189-190, 301 Allenic sulfones, 395 Allylacetophenone, 7-8 AUylbenzene, 292 Allyl bromide, 133, 292 Allyl diazoacetate, 222 Allyl esters, 302 Allyl ethers, 136-137 Allylic acetates, 176, 534 Allylic alcohols, 6, 136, 141, 142, 179, 191, 260, 335, 346, 373, 379-380, 427, 428, 445, 451-452,534 r-AUylic alcohols, 426-427 Allylic amination, 43 Allylic amines, 176 Allylic carbamates, 316 Allylic chlorides, 516 Allylic esters, 173, 243 Allylic ethers, 534 Allylic halides, 334-335 Allylic hydroperoxides, 247, 316, 317, 370... 

Allylic acetate 110 was obtained by regioselective hydroacetoxylation of phenylal-lene at the terminal double bond. DPPF is the most effective ligand. The reaction is explained by hydropalladation of allene with H-Pd-OAc to form 7r-allylpalladium acetate 111 and reductive elimination [33]. 

In 1996, Allen and Williams demonstrated that the DKR of allylic acetates could be accomplished through coupling palladium-catalysed racemisation and enzymatic hydrolysis of allylic acetates in buffer solution. However, the DKR under these conditions was limited to cyclohexenyl acetates to yield symmetrical palladium-allyl intermediates. Among them, 2-phenyl-2-cyclohexenyl acetate was the only substrate to have been resolved with good results (81% yield, 96% ee), as shown in Scheme 4.60. 

Takahashi reported a novel Pd-catalyzed cyclization of allylic acetate and allenic moietyJ" The reaction is discriminated by the number of tethered carbon chains, as... 

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