Palladium-Catalyzed Electrophilic Allylation Reactions via Bis(allyl)palladium Complexes and Related Intermediates

The synthetic scope of the allyl–palladium chemistry can be extended to involve electrophilic reagents. The greatest challange in these reactions is the catalytic generation of an allyl–palladium intermediate incorporating a nucleophilic allyl moiety. A vast majority of the published reactions that involve palladium‐catalyzed allylation of electrophiles proceed via bis(allyl)palladium intermediates. The η1‐moiety of the bis(allyl)palladium intermediates reacts with electrophiles, including aldehydes, imines, or Michael acceptors. Recently, catalytic electrophilic allylations via mono‐allylpalladium complexes were also presented by employment of so‐called “pincer complex” catalysts. Catalytic allylation of aldehyde, imine, and Michael acceptor substrates can be achieved by using palladium catalysts (see scheme). These transformations proceed through (η1‐allyl)palladium complexes, in which the allyl moiety is nucleophilic. This concept paper discusses the rationalization of the nucleophilic reactivity of (η1‐allyl)palladium complexes and the synthetic utility of the palladium‐catalyzed electrophilic substitution reactions.