Dramatic catalyst evolution in the asymmetric addition of diethylzinc to benzaldehyde

We have observed product ee's that begin at 20% at low reaction conversion and rise to 79% ee at the completion of the reaction in the asymmetric addition of alkyl groups to benzaldehyde. This rare behavior is attributed to autoinduction, in which the catalyst evolves by incorporation of the product. Based on this, we have been able to optimize the catalyst by variation of achiral, rather than enantiopure ligands.

Large changes in enantioselectivity are observed during the asymmetric addition of diethylzinc to benzaldehyde catalyzed by bis(sulfonamide) ligands 5a–c.Figure optionsDownload full-size imageDownload as PowerPoint slide