Enantioselective addition of diethylzinc to aldehydes catalyzed by (R)-1-phenylethylamine-derived 1,4-amino alcohols

A series of o-xylylene-type 1,4-amino alcohols, synthesized from (R)-1-phenylethylamine, were used as chiral ligands for the enantioselective addition of diethylzinc to benzaldehyde. (S)-1-Phenyl-1-propanol was obtained with high enantioselectivity in all cases since the stereochemical outcome of the reaction was controlled by the chiral benzylic carbon bearing amino group. Highest catalytic activity was obtained by using (R)-1-{2-[1-(pyrrolidin-1-yl)ethyl]phenyl}cyclohexan-1-ol (1n) derived from (R)-1-(1-phenylethyl)pyrrolidine and cyclohexanone. Various chiral secondary alcohols were obtained by the reaction of diethylzinc and aldehydes in the presence of 1n within 2 h with good to high enantioselectivities.