Hyperpositive nonlinear effects in asymmetric catalysis
Résumé
Asymmetric amplification is a curious phenomenon which is believed to play a 10 key role in the emergence of biological homochirality, and thus of life itself. In 11 asymmetric catalysis, it is achieved via positive non-linear effects, which allow 12 high product enantiomeric excesses with a non-enantiopure catalyst. However, 13 it has also been proposed that non-enantiopure catalysts may be even more 14 enantioselective than their enantiopure counterparts, though such a case has 15 never been experimentally observed to date. Here we show an example of such 16 a hyperpositive non-linear effect in asymmetric catalysis. We found that 17 addition of dialkylzinc reagents to benzaldehyde gave higher product e.e.s with 18 only partially resolved chiral N-benzyl-ephedrine ligands. A mechanistic study 19 was carried out and our results point toward a two-component catalysis, where 20 mononuclear as well as aggregated catalysts are in equilibrium and in 21 competition. These results introduce an unprecedented class of asymmetric 22 amplification in enantioselective catalysis. 23 24 Introduction 25
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