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.