Fig. 5: Reaction mechanism investigation.

a Control experiments with modified chiral aldehyde catalysts. b Control experiments to investigate the role of nickel and ZnCl2. c Control experiments with Schiff base as reactants. d The nonlinear effect investigation between the ee value of product 4a and chiral sources 3i or L1. e The possible catalytic cycles. (x = the equivalents of Ni(COD)2, y = the equivalents of ZnCl2).