A Mechanistic Insight into the Ligand-Controlled Asymmetric Arylation of Aliphatic α-Amino Anion Equivalents: Origin of Regio- and Enantioselectivities.

Abstract

The reaction mechanism and the origins of regio- and enantioselectivities for Pd-catalyzed asymmetric arylation of aliphatic α-amino anion equivalents were investigated computationally. The results indicate that the reaction proceeds via mainly six sequential steps: deprotonation at α'-site of imine, coordination of α-amino anion to Pd-catalyst, oxidative addition, transmetalation, reductive elimination, as well as the final dissociation to release the product and regenerate the catalyst. The transmetalation is a key step on which both enantioselectivity and regioselectivity depend. The charge inversions of α- and α'-C atoms and the orbital interaction between Pd center and α-C in transmetalation step are responsible for the regioselectivity. Additionally, the intermediates before the dissociation step are critical in controlling the enantioselectivity. Noncovalent interactions analyses indicate that the enantioselectivity primarily arises from the CH···π interactions of isopropyl (iPr) groups with the fluorene and the benzene rings for PdL1-catalyzed reaction.