AUyl acetates palladium-catalyzed

The chloroacetoxylation proceeds via the same type of intermediate as that involved in the palladium-catalyzed 1,4-diacetoxylation that is, via a 4-acetoxy-l,2,3- [t-allylpalladium intermediate (cf Scheme 11.9). The high selectivity for unsymmetrical products (usually >98%) is remarkable. Since chloride anion is the strongest nucleophile of the two present (Cl and AcO ), 4-chloro-7t-aUyl-palladium intermediate 68 is initially formed (Scheme 11.22). However, the chloride in the 4-position is rapidly exchanged for acetate to give a more stable rt-allyl intermediate 69, which leads to product. The presence of the intermediate 68 was confirmed by its trapping with a faster oxidant (isoamyl nitrite) than p-BQ, which furnished l,4-dichloro-2-alkene [89],(J.E. BackvaU, unpublished results). In the case of 1,3-cyclohexadiene, this product was ds-l,4-dichloro-2-cyclohexene (J.E. BackvaU, unpublished results). 

More recently, allylic carbonates 115 have been found to conple with alkenylfluo-rosilanes in the presence of a paUadinm catalyst to yield the corresponding 1,4-dienes (equation 93). The corresponding palladium-catalyzed reaction of allylsilane with aUyl acetate 116 has been explored (eqnation 94). ... 

The palladium-catalyzed carbocyclization of allylic acetates with alkenes is a powerful method for the formation of five- and six-member rings. The reaction initiates throngh the formation of a rt-aUyl palladium complex followed by carbometaUation of the second double bond. The formed palladium complex is then eliminated to produce commonly the cyclized 1,4-dienes (Scheme 7.48). 

Intramolecular reactions ofallylic acetates with conjugated dienes catalyzed by Pd(0) lead to a 1,4-addition of a carbon and an oxygen to the diene. The reaction, which is formally an isomerization, involves two different 7t-allyl complexes (Scheme 11.5) [49]. Reaction of 28 in the presence of the Pd(0) catalyst Pdjldba), CHClj and LiOAc/HOAc in acetonitrile under reflux produces the cycHzed isomer 31 in 62% yield. The double bond had exclusively ( )-configuration, while the configuration on the ring was a mixture of cis and trans. Oxidative addition of the allylic acetate to the Pd(0) species gives the intermediate it-aUyl complex 29. Subsequent insertion of a diene double bond into the allyl-palladium bond produces another it-allyl intermediate 30, which is subsequently attacked by acetate to give the product 31. 

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