Showing papers by "Xiaohua Liu published in 2007"

Highly Enantioselective Henry (Nitroaldol) Reaction of Aldehydes and α-Ketoesters Catalyzed by N,N‘-Dioxide-Copper(I) Complexes

Abstract: A new chiral N,N'-dioxide-Cu(I) catalyst has been developed for the asymmetric Henry (nitroaldol) reaction. The approach benefited from the easy modification of the chiral space. As the highly effective N-oxide ligand, 1d has been adopted for the Henry reaction with both aromatic and heteroaromatic aldehydes. The corresponding nitro-alcohol products were obtained in good yields with high enantiomeric excesses up to 98%. Moreover, alpha-ketoesters were also catalyzed by this catalyst to give attractive optically active alpha-hydroxy beta-nitro esters containing chiral quaternary carbon centers (up to 99% ee). On the basis of a combination of several techniques including the 1H NMR, ESI-HRMS, and MM2 calculations, the proposed mechanism was presented to explain the origin of reactivity and asymmetric inductivity.

Asymmetric Cyanoethoxycarbonylation of Aldehydes Catalyzed by Heterobimetallic Aluminum Lithium Bis(binaphthoxide) and Cinchonine

Abstract: Highly efficient catalytic asymmetric cyanoethoxycarbonylation of aldehydes was achieved by 10 mol % cinchonine with 10 mol % heterometallic (S)-aluminum lithium bis(binaphthoxide), which gave the cyanohydrins ethyl carbonates in excellent isolated yields (up to 99 %) with moderate to high enantioselectivities (up to 95 % ee) under mild conditions (at −20 °C). Especially, the solid aluminum lithium bis(binaphthoxide) free of tetrahydrofuran was obtained by a new procedure using (S)-bi(2-naphthol), aluminum isopropoxide and n-butyllithium in dichloromethane, which was insensitive to air and moisture and was very convenient to store and use. A catalytic cycle based on experimental phenomena was proposed to explain the nature of the asymmetric induction.