Communications Highly Enantioselective Addition of Diethylzinc to Aldehydes

Enantioselective alkylation of carbonyl compounds is a challenged domain of asymmetric C-C bond formation.1 Particularly, asymmetric addition of diethylzinc to aldehydes is one of the important synthetic methods for the preparation of optically active secondary alcohols, and numerious efforts have been made to find effective chiral ligands.2 To date, most of the successful results were obtained by using sterically constrained β-amino alcohols such as N,N-dialkylated norephedrine derivatives.3 Extensive studies by Soai on the effect of ligand structure on enantioselectivity indicated that the chain length of the N-alkyl substituent is very imporant. Thus, the catalyst with N-alkyl substituents of a chain length of four carbons, 1 (DBNE), gave the best results in dialkylzinc addition to various aliphatic (87-93% ee) and aromatic (90-95 % ee) aldehydes. It has been recentl