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三、羰基化合物的不对称反应 (一) 羰基的不对称催化氢化在非均相系统中,以手征性物质修饰的金属催化剂,对羰基化合物的不对称催化氢化,也曾进行过广泛地研究。与烯烃和烯胺一样,看来很少有制备价值。近年来,用酒石酸修饰的活性镍催化氢化乙酰乙酸乙酯,进行了较多研究。发现其对映体过量与转化率有关。当转化率为10％时,生成的(-)3-羟基丁酸乙酯的对映体过量为最高,约55％ee。此种活性镍吸附着的乙酰乙酸乙酯,从红外光谱看,其羰基吸收弱,烯醇吸收强,所以它的催化氢化主要以烯醇式进行。当活性镍中添加有少量钯或铂,使它们共存于硅藻土载体上,以酒石酸修
Asymmetric Oxidation of Carbonyl Compounds (I) Asymmetric Catalytic Hydrogenation of Carbonyls Asymmetric catalytic hydrogenation of carbonyls has also been extensively studied in heterogeneous systems with metal catalysts modified with chiral substances . Like olefins and enamines, there appears to be little preparative value. In recent years, tartaric acid-modified nickel catalyzed hydrogenation of ethyl acetoacetate has been studied. The enantiomeric excess was found to be related to conversion. At 10% conversion, the resulting enantiomeric excess of (-) 3-hydroxybutyrate was the highest at about 55% ee. The ethyl acetoacetate adsorbed on this active nickel shows weak carbonyl absorption and strong enolase absorption from infrared spectroscopy. Therefore, its catalytic hydrogenation mainly proceeds in the enol form. When active nickel is added a small amount of palladium or platinum, so that they coexist on the diatomaceous earth carrier to tartaric acid repair