Asymmetric Allylic Alkylation of β-Ketoesters via C-N Bond Cleavage of N-Allyl-N-methylaniline Derivatives Catalyzed by a Nickel-Diphosphine System

Nickel complexes bearing chiral diphosphine ligands, such as (S)-Tol-MeO-BIPHEP and (S)-H-8-BINAP, serve as efficient catalysts for asymmetric allylic alkylation (AAA) of beta-ketoesters, using allylic amines as ally! sources. The reactions proceed with high catalytic activity and high enantioselectivity. N-Methyl-N-phenyl allylic amines were indispensable to achieve the high catalytic activity, to achieve the high enantioselectivity, and to expand the substrate scope to 5- and 7-membered beta-ketoesters, whose nickel-catalyzed AAA with allylic alcohols results in low enantioselectivity. On the basis of the kinetics using a catalyst system made of Ni(cod)(2) and (S)-Tol-MeO-BIPHEP, and DFT calculations for the reaction pathway of the AAA reaction mediated by an isolated olefin-coordinated nickel-DPPF complex 4b, we propose a mechanism where protonation of the nitrogen atom of the coordinating allylic amine by beta-ketoester is key to cleaving the C-N bond and delivering a cationic pi-allyl nickel(II) intermediate.