Noyori R, Suga S, Oka H, Kitamura M
Department of Chemistry and Research Center for Materials Science, Nagoya University, Chikusa.
Chem Rec. 2001;1(2):85-100. doi: 10.1002/tcr.1.
Asymmetric addition of dialkylzincs to aldehydes in the presence of (2S)-3-exo-(dimethylamino)isoborneol [(S)-DAIB] exhibits various nonclassical phenomena. The enantiomeric excess (ee) of the alkylation product, obtained with partially resolved DAIB, is much higher than that of the chiral amino alcohol, while the rate decreases considerably as the ee of DAIB is lowered. The asymmetric amplification effects reflect the relative turnover numbers of two enantiomorphic catalytic cycles, where an essential feature is the reversible homochiral and heterochiral dimerization of the coexisting enantiomeric DAIB-based Zn catalysts. The interplay between the thermodynamics of the monomer/dimer equilibration and the kinetics of alkylation reaction strongly affect the overall profile of asymmetric catalysis. The self and nonself recognition of the chiral Zn catalysts is a general phenomenon when (S)-DAIB is mixed with its enantiomer, diastereomer, or even an achiral beta-amino alcohol. The degree of nonlinearity is highly affected not only by the structures and purity of catalysts but also by various reaction parameters. The salient features have been clarified on the basis of molecular weight measurements, NMR and X-ray crystallographic studies of organozinc complexes, and kinetic experiments, as well as computer-aided quantitative analysis.
在(2S)-3-外向-(二甲基氨基)异冰片醇[(S)-DAIB]存在下，二烷基锌与醛的不对称加成表现出各种非经典现象。用部分拆分的DAIB得到的烷基化产物的对映体过量(ee)远高于手性氨基醇的对映体过量，而随着DAIB的ee降低，反应速率显著下降。不对称放大效应反映了两个对映体催化循环的相对周转数，其中一个基本特征是共存的基于对映体DAIB的锌催化剂的可逆同手性和异手性二聚化。单体/二聚体平衡的热力学与烷基化反应动力学之间的相互作用强烈影响不对称催化的整体情况。当(S)-DAIB与其对映体、非对映体甚至非手性β-氨基醇混合时，手性锌催化剂的自我和非自我识别是一种普遍现象。非线性程度不仅受到催化剂结构和纯度的高度影响，还受到各种反应参数的影响。基于分子量测量、有机锌配合物的核磁共振和X射线晶体学研究、动力学实验以及计算机辅助定量分析，已经阐明了这些显著特征。
