Ligands with cycloalkane backbones VIII. Steric effects in the ligand accelerated enantioselective alkylation of benzaldehyde

Alkylation of benzaldehyde with diethylzinc was carried out in the presence of a series of (1S,2S)-2-(pyrazol-1-yl)cyclohexanols. Depending on the substituent at pyrazole, the 1-phenylpropanols were obtained with 18–97% yield and 2–76% enantiomeric excess. However, the increase in activity is not parallel to the increase in stereoselectivity, which supports the reaction mechanism, proposed by Noyori.