Asymmetric addition of n-butyllithium to aldehydes: new insights into the reactivity and enantioselectivity of the chiral amino ether accelerated reaction

Enantioselective butylation of benzaldehyde with n-butyllithium was mediated by a series of chiral lithium amide analogues to give 1-phenylpentanol in good to moderate enantioselectivities. In order to achieve high enantiomeric excess in the reaction, the lithium amide must have a substituent larger than methyl on both the carbon at the stereogenic center and the nitrogen. Computational studies, using semi-empirical (PM3) and density functional (B3LYP) methods, show that the stabilities of the transition states for the chiral lithium amide accelerated butylation of isobutyraldehyde are in agreement with experiments.