Palladium-allyl complexes stoichiometric attack

Cyclic ethers and amines can be formed if the nucleophile is an intramolecular alcohol or amine. Stoichiometric palladium can be avoided by using benzoquinone as the stoichiometric oxidant with a catalytic amount of palladium. In this example intramolecular oxypalladation of a diene is followed by attack of an external nucleophile on a TC-allyl complex. 

Attempts to employ allenes in palladium-catalyzed oxidations have so far given dimeric products via TT-allyl complexes of type 71 2,63 pjjg f ct that only very little 1,2-addition product is formed via nucleophilic attack on 7r-allyl complex 69 indicates that the kinetic chioropaiiadation intermediate is 70. Although formation of 70 is reversible, it is trapped by the excess of allene present in the catalytic reaction to give dimeric products. The only reported example of a selective intermolecuiar 1,2-addition to allenes is the carbonyiation given in equation 31, which is a stoichiometric oxidation. ... 

Allylpalladium complexes find wide application in organic synthesis. With carbon nucleophiles they form new C—C bonds, thus providing a method for building carbon skeletons. Dimeric allylpalladium chlorides are not very susceptible to attack by nucleophiles, but their reactivity can be enhanced by addition of triphenylphosphine, which converts them into monomeric species. These reactions, however, are stoichiometric in palladium, which is undesirable on account of its high cost. Fortunately related catalytic procedures have been discovered. Many allylic compounds react with Pd(PPhj4 (p. 181) to form cationic -allyl complexes. These cations react with nucleophiles to form substituted allylic derivatives, while the catalyst, effectively PdL , is regenerated and reenters the cycle. 

Similar solvent effects are observed in the stoichiometric formation of bridged (t/3-allyl)palladium trifluoroacetates40. A mixture of tetrahydrofuran and acetonitrile favors anti addition to yield the ra-adduct 19, whereas syn addition dominates in pure tetrahydrofuran. syn Attack of palladium(O) is much slower. The main effect of the polar coordinating solvent is to stabilize the transition state of the anti addition, in which charge separation is necessarily involved to a higher extent than for syn addition. The reaction conditions in the two reactions shown below represent feasible methods of preparing stable 7t-allylpalladium complexes 20. Palladium black will precipitate in the second reaction, if phenanthroline is not present. 

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