Mischmetall, an alloy of the light lanthanides, has been used in a variety of organicreactions, either as a coreductant in samarium(II)-mediated reactions (Barbier and Grignard-type reactions, pinacoliccouplingreactions) or as the promoter of Reformatsky-type reactions. It has been also employed as the starting material for easy syntheses of lanthanide trihalides, the reactivity of which has been
catalyzed aldolreaction of trimethylsilylenolates with aldehydes is established in DMF or pyridine solvent by using a Lewis base such as lithium diphenylamide (Tables 4 and 5) or lithium 2-pyrrolidone (Tables 6–8). The effect of solvent suggests that this reaction proceeds via the pentacoordinated hypervalent silicate generated by the coordination of the above Lewis base to a trimethylsilylenolate. Successive
Lithium Acetate-Catalyzed Aldol Reaction between Aldehyde and Trimethylsilyl Enolate in Anhydrous or Water-Containing<i>N</i>,<i>N</i>-Dimethylformamide
AcOLi catalyst, the aldolreaction in water-containing DMF was studied in detail. AcOLi and various metal carboxylates behaved as effective Lewis base catalysts in aldolreactionsbetweentrimethylsilylenolate and aldehydes in DMF-H 2 O (50:1) (Tables 6, 7). One of the most characteristic points of the above reaction that took place in water-containing DMF is that the aldehydes having a free amide
乙酸锂 (AcOLi) 催化的三甲基甲硅烷基烯醇化物和醛之间的醛醇反应在无水 DMF 或吡啶中顺利进行,在弱碱性条件下以良好至高产率提供相应的醛醇(表 1-5)。这种催化羟醛反应也可以通过使用其他金属羧酸盐顺利进行,这些金属羧酸盐通过用碳酸锂 (Li 2 CO 3 ) 处理羧酸很容易原位制备(表 2,方案 5)。为了展示温和易得的AcOLi催化剂的效果,详细研究了含水DMF中的羟醛反应。AcOLi 和各种金属羧酸盐在 DMF-H 2 O (50:1) 中三甲基甲硅烷基烯醇酯和醛之间的羟醛反应中充当有效的路易斯碱催化剂(表 6、7)。在含水DMF中发生的上述反应的最特征点之一是具有游离酰胺和羟基甚至羧基的醛反应平稳并以中等至高产率提供所需的醛醇29-31(表 8,条目 12-15)。由羧酸酯衍生的三甲基甲硅烷基烯醇化物在上述反应中表现得与优异的亲核试剂相似。这是路易斯碱催化醛醇反应的第一个例
Homogeneous catalysis. transition metal based lewis acid catalysts.
作者:T. Keith Hollis、William Odenkirk、N.P. Robinson、John Whelan、B. Bosnich
DOI:10.1016/s0040-4020(01)87259-8
日期:1993.1
Transition metal basedLewisacids provide catalysts for the Diels-Alder and Mukaiyama reactions. These catalysts must possess an electron deficient axophilic metal center and a labile coordination position. Unlike traditional Lewisacids, those derived from transition metals can function in the presence of water and have welldefined structures. It is shown how a normally electron rich ruthenium atom
A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the reaction of both aldehydes and acetals with silylenolethers or ketene silylacetals to give the corresponding aldol adducts in moderate to high yields. The remarkable high catalytic activity of Al-MCM-41 over amorphous silica-alumina and aluminum-free mesoporous silicate was observed in the reaction