Hyperpositive nonlinear effects in asymmetric catalysis

Asymmetric amplification is a curious phenomenon that is believed to play a key role in the emergence of biological homochirality, and thus of life itself. In asymmetric catalysis, it is achieved via positive nonlinear effects, which allow high product enantiomeric excesses with a non-enantiopure catalyst. However, it has also been proposed that non-enantiopure catalysts may be even more enantioselective than their enantiopure counterparts, although such a case has never been experimentally observed so far. Here, we present an example of such a hyperpositive nonlinear effect in asymmetric catalysis. We found that addition of dialkylzinc reagents to benzaldehyde gave higher product enantiomeric excesses with only partially resolved chiral N -benzyl-ephedrine ligands. A mechanistic study was carried out and our results point towards a two-component catalysis, where mononuclear as well as aggregated catalysts are in equilibrium and in competition. These results introduce an unprecedented class of asymmetric amplification in enantioselective catalysis.