Enantioselective additions of diethylzinc to aldehydes catalyzed by titanate(IV) complex with chiral bidentate bis-amide ligands based on cyclopropane backbone

Abstract

A set of chiral bis-amide ligands (4a–d and 5a–d) were obtained easily from readily available starting materials in a straightforward manner via acid chloride reaction of the parent Feist’s acid. These ligands have been tested as chiral catalysts for the enantioselective addition of diethylzinc to aromatic aldehydes in the presence of Ti(OiPr)4 as a co-additive. Very good enantioselectivity was obtained for 4-bromobenzaldehyde while in the case of 2,4-dichlorobenzaldehyde very low enantioselectivity was observed. The influence of solvent, temperature and the alkyl group substituents has been studied, and in the best case, an enantiomeric excess upto 95% has been achieved by using only 10 mol % of the chiral bis-amides ligand 5b.

Keywords

• C2 symmetric bis-amide ligand
• Diethylzinc addition
• Enantioselective catalysis