Active Pd(II) Complexes as Either Lewis Acid Catalysts or Transition Metal Catalysts
The new frontier of asymmetric catalyses by Pd(II) complexes is reviewed. Asymmetric catalyses of carbon–carbon bond formation by Pd(II) complexes are divided into transition metal catalysis and Lewis acid catalysis. Transition metal catalyses are observed in anomalous six-membered ring formation, ene-type cyclization leading to five-membered rings, spiro cyclization, alkaloid and quinoline synthesis, Suzuki–Miyaura coupling, C–H bond activation/C–C bond formation, and Claisen rearrangement. Lewis acid catalyses take place in the carbonyl–ene reaction, hetero Diels–Alder reaction, Friedel–Crafts reaction, and aldol reaction. The specific mechanisms and deep insights into the key reaction intermediates or active organopalladium species are discussed on the basis of the new design of neutral and cationic Pd(II) complexes with chiral ligands.
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