Cooperative Catalyst-Enabled Regio- and Stereodivergent Synthesis of α-Quaternary α-Amino Acids via Asymmetric Allylic Alkylation of Aldimine Esters with Racemic Allylic Alcohols

We describe cooperative bimetallic catalysis that enables regio-/stereodivergent asymmetric alpha-allylations of aldimine esters. By employing Et3B as the key activator, racemic allylic alcohols can be directly ionized to form Pd or Ir-pi-allyl species in the presence of achiral Pd or chiral Ir complexes, respectively. The less or more substituted allylic termini of the metal-pi-allyl species are amenable to nucleophilic attack by the chiral Cu-azomethine ylide, the formation of which is simultaneously facilitated by Et3B, affording alpha-quaternary alpha-amino acids with high regioselectivity and excellent stereoselectivity. The use of readily available allylic alcohols as electrophilic precursors represents an improvement from an environmental and atom/step economy perspective. Computational mechanistic studies reveal the crucial role of the Et3B additive and the origins of stereo- and regioselectivities by analyzing steric effects, dispersion interactions, and frontier orbital population.

Automated summary

Cooperative bimetallic catalysis enables regio-/stereodivergent asymmetric alpha-allylations of aldimine esters. By employing Et3B as the key activator, racemic allylic alcohols can be directly ionized to form Pd or Ir-pi-allyl species in the presence of achiral Pd or chiral Ir complexes, respectively. The reaction exhibits high regioselectivity and excellent stereoselectivity.