Origin of the Minor Enantiomeric Product in a Noyori Asymmetric Hydrogenation: Evidence for Pathways Different to the Major Mechanism

Hidden pathways: The enantiomeric products of the catalytic hydrogenation of an isotopically labeled substrate were separated. The ratios of the isotopomers revealed that the major and minor enantiomers are formed mostly through different mechanisms. Hence, when analyzing the energy profile of an asymmetric catalytic reaction with the Arrhenius equation, two competing diastereomorphic catalytic cycles should be considered (see scheme).