Stereoselective Synthesis of Norephedrine and Norpseudoephedrine by Using Asymmetric Transfer Hydrogenation Accompanied by Dynamic Kinetic Resolution

Each of the enantiomers of both norephedrine and norpseudoephedrine were stereoselectively prepared from the common, prochiral cyclic sulfamidate imine of racemic 1-hydroxy-1-phenyl-propan-2-one by employing asymmetric transfer hydrogenation (ATH) catalyzed by the well-defined chiral Rh-complexes, (S,S)- or (R,R)-Cp*RhCl­(TsDPEN), and HCO₂H/Et₃N as the hydrogen source. The ATH processes are carried out under mild conditions (rt, 15 min) and are accompanied by dynamic kinetic resolution.