Palladium complexes allyhc reactions

The reaction of this allyHc acetate with the sodium salt of Meldrum s acid (structure in margin) demonstrates the retention of configuration in the palladium(0)-catalysed process. The tetraacetate and the intermediate Jt-allyl complex are symmetrical, thus removing any ambiguity in the formation or reaction of the Jt-allyl complex and hence in the regiochemistry of the overall reaction. 

Vinyl epoxides and allyHc carbonates are especially useful electrophiles because under the influence of palladium(O) they produce a catalytic amount of base since is an alkoxide anion. This is sufficiently basic to deprotonate most nucleophiles that participate in aUylic alkylations and thus no added base is required with these substrates. The overaU reaction proceeds under almost neutral conditions, which is ideal for complex substrates. The rehef of strain in the three-membered ring is responsible for the epoxide reacting with the paUadium(O) to produce the zwitterionic intermediate. Attack of the negatively charged nucleophile at the less hindered end of the Jt-allyl palladium intermediate preferentially leads to overall 1,4-addition of the neutral nucleophile to vinyl epoxides. 

The first use of chiral helical polymers bearing no chiral side chains for chiral reaction induction was realized by Reggelin et at. in 2002 [69]. Two poly(methyl methacrylate)-based chiral polymers (40) was prepared by hehx-sense selective anionic polymerization of sterically congested methacrylates with a chiral base mixture as initiator. The pyridine moieties in helical polymers allowed various metal coordinations [70] or formation of ionic pairs [71]. Their complexes with palladium precursor were found to be active catalysts for the allyHc substitution reaction of l,3-diphenylprop-2-enyl acetate (Figure 4.36). Although the ee values were only moderate (<33%), this research opened up a new area for asymmetric catalysis with unnatural helical chiral polymers. 

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