Immobilization of chiral amide derived from (1R,2S)-(-)-norephedrine over 3D nanoporous silica for the enantioselective addition of diethylzinc to aldehydes

Abstract

Chiral amide synthesized from (1R,2S)-(-)-norephedrine has been successfully immobilized onto three dimensional Ia3d cubic nanoporous material. The immobilization of the chiral amide has been confirmed by using various physiochemical techniques. The immobilized ligand has been screened for its catalytic activity in the enantioselective addition of diethylzinc to aromatic aldehydes. The immobilized catalyst was found to be highly active and selective, affording the final product chiral alcohols in 92% yield with a 95% ee at room temperature. The enantioselectivity of the immobilized catalyst is much higher than that of the homogenous catalyst (40% ee) at room temperature. In addition, the catalyst was stable and found to be purely heterogeneous and recyclable. The activity of the immobilized catalyst has been also investigated for the aromatic aldehydes with different electron donating and withdrawing groups. In addition, the electronic and steric effects of the substrates affecting the activity and the enantioselectivity of the catalysts were discussed in detail. © 2011 Elsevier Inc. All rights reserved.