Electrophilic attack, organopalladium

A second type of organopalladium intermediates are 7r-allyl complexes. These complexes can be obtained from Pd(II) salts and allylic acetates and other compounds with potential leaving groups in an allylic position.79 The same type of 7i-allyl complexes can be prepared from alkenes by reaction with PdCl2 or Pd(02CCF3)2.80 The reaction occurs by electrophilic attack on the n electrons followed by loss of a proton. The proton loss probably proceeds via an unstable species in which the hydrogen is bound to... 

Even without mechanistic information, one can begin to rationalize and, perhaps more importantly, predict various catalytic organopalladium reactions in consultation with Table 3 and Scheme 3. For example, the following four reactions shown in Scheme 5 are representative of the four most important types of Pd-catalyzed C—C bond formation processes discussed in detail in Parts III-VI. It is useful to note that only four patterns in Table 3, that is, (i) carbopalladation, (ii) reductive elimination, (iii) migratory insertion, and (iv) nucleophilic (or electrophilic) attack on ligands, can achieve C—C bond formation. This summary can also be appropriately modified for the formation of other types of bonds, such as C—H, C— M, C— X, and X— X bonds, where M is a metal and X is a heteroatom. 

The first reported example of an intramolecular nucleophilic attack on an unsaturation electrophilically activated by an organopalladium complex dates back to 1987. In this new reaction the activating species is generated in situ by oxidative addition of an unsaturated halide to the metal. The cyclization process generates a cr-bonded palladium complex, which undergoes reductive elimination. This liberates the cyclization product and completes the catalytic cycle (Scheme 15). 

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