Fig. 6: Amino acid schiff bases for unnatural α-amino acid synthesis.

a Synergistic Cu/Pd catalysis³⁰. b Synergistic Cu/Ni catalysis³¹. c Synergistic Cu/Ir catalysis³⁴. d Aldehyde/Pd catalysis to afford α,α-disubstituted α-amino esters without the preparation of Schiff bases³⁵.