Modular Prolinol Chiral Ligands for Enantioselective Addition of Diethylzinc to Aromatic Aldehydes

Enantioselective addition of diethylzinc (ZnEt2) to a series of aromatic aldehydes was promoted using a modular prolinol chiral ligand, 2-(S)-2-(hydroxydiphenylmethyl)pyrrolidin-1-yl)methyl)-4-nitrophenol (1a), without using titanium complex. The catalytic system employing 15 mol% of 1a was found to promote the addition of diethylzinc to a wide range of aromatic aldehydes with electron-donating and electron-withdrawing substituents, giving up to 86% ee of the corresponding secondary alcohol under mild conditions.