4.5 C–C Bond Formation by Metal-Catalyzed Asymmetric Allylic Alkylation

Abstract

A low-valent metal complex can react with an allylic compound to produce a π-allyl metal complex, which is attacked by various nucleophiles and electrophiles to produce allylated compounds. Although many metals can be formed into a π-allyl metal complex, the palladium complex is most important and useful above all. In 1963, Tsuji found that allyl chloride could react with CO using a stoichiometric amount of palladium complex to afford a carbonylated compound and they found that the intermediate was a π-allyl metal complex. Then Trost developed this reaction to palladium-catalyzed allylic alkylation. When palladium complex with chiral ligand is used in the allylic alkylation, a chiral allylated compound is produced. As for the ligand, various phosphine ligands were designed and synthesized. As a result, allylated compounds with high ee were obtained. Using this method, many natural products and related compounds could be synthesized. Other metals, such as nickel, molybdenum, iridium, and tungsten could also react with allylic compound to form π-allyl metal complexes, which are useful intermediates in synthetic organic chemistry. Thus, these metal complexes with a chiral ligand could also be used for an asymmetric allylic alkylation.