Optimization of asymmetric catalysts using achiral ligands: metal geometry-induced ligand asymmetry.

[reaction: see text] Traditionally, asymmetric catalysts have been optimized by modification of resolved chiral ligands. In this Letter, we optimize the asymmetric addition of diethylzinc to aldehydes by modification of achiral methylene bis(phenol) ligands. Upon coordination of the substrate, the achiral ligand becomes asymmetric, a concept termed Metal Geometry-Induced Ligand Asymmetry. The enantioselectivity of the catalyst formed from a single resolved ligand and several achiral ligands ranged from 9% (R) to 83% (S).

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