Picolinaldehyde-Zinc(II)-Palladium(0) Catalytic System for the Asymmetric α-Allylation of N-Unprotected Amino Esters.

Reported in this work is a synergistic ternary achiral picolinaldehyde-Zn(II)-chiral palladium complex system for the highly enantioselective α-allylation of N-unprotected amino esters. By utilizing a variety of allylic carbonates or vinyl benzoxazinanones as substrates, α-allyl α-amino esters were obtained in high yields (up to 96 %) with high enantioselectivities (up to 98 % ee). Control experiments suggest that the coordination of Zn(II) with the Schiff base intermediate enhances the acidity of the α-C-H bonds of amino esters, thereby favoring α-allylation over intrinsic N-allylation. Furthermore, NMR studies reveal an interaction between the chiral palladium complex and the Zn(II)-Schiff base intermediate, leading to the formation of a picolinaldehyde-Zn(II)-Pd(0) catalytic system.