Fig. 4: Control experiments.

a The effect of chiral Lewis base catalyst. b The effect of acid. c The effect of HFIP. d The effect of N-H group of the substrate. e Kinetic experiment (blue line for 4a’, orange line for 4a, green line for 2a). f The conversion from 4a’ to 4a. Standard conditions: The reaction was conducted with (S, R)-1g (0.01 mmol), pTSA (0.01 mmol), HFIP (0.2 mmol), and 3 Å MS (40 mg) in DCM (2.0 mL) at −10 °C under Ar for 22 h. pTSA = p-toluenesulfonic acid, PA = 1,1’-binaphthyl-2,2’-diyl hydrogenphosphate, HFIP = hexafluoroisopropanol.