METAL MEDIATED ASYMMETRIC INTRAMOLECULAR HYDROSILATION

烯烃的水合和酮的还原起着重要作用， 的综合战略建设的重要作用 生物活性分子。 目前的水化方法 通过例如硼氢化或氧汞化， 用硼或铝还原酮 主要是化学计量的转变。 尽管许多 这些反应中的一种已经对映选择性地进行， 产生对映体产物，化学选择性差， 酯和酰胺基团通常在竞争中被还原。 此外，不对称催化的例子很少。 分子内不对称催化硅氢化提供了一种 烯烃化学选择性水合的有吸引力的解决方案， 酮的减少。 该提案旨在发展 不对称催化硅氢化反应的新型手性催化剂。 一 机械的合理化是提供这表明，某些 容易获得的衬底将产生高的光学产率， 一个分子内的过程。 该战略采用了熟悉的概念 的歧视，通过优先的环状构象， 对映选择性过渡位点。 硅氢加成的产物容易转化为光学活性的化合物。 活性1，4-、1，3和1，2-二醇。 这些二元醇是关键的 大环内酯类和离子载体类化合物的合成原料。 该建议还针对一个重要的方法问题。 这涉及选择正确的催化剂的问题， 将给出高光学产率的衬底。 为此目的， 建议研究反应的机理， 以确定对映体选择性的起源。 等 研究将为其他催化剂的设计提供基础。 转变

The hydration of olefins and the reduction of ketones play an important role in the synthetic strategies for the construction of biologically active molecules. The current methods of hydration of olefins by, for example, hydroboration or oxymercuration and reduction of ketones by, for example, boron or aluminum hydrides are, in the main, stoichiometric transformations. Although many of these reactions have been carried out enantioselectively to produce enantiomeric products, the chemoselectivity is poor in that ester and amide groups are generally reduced in competition. Moreover, there are few examples of asymmetric catalysis. Intramolecular asymmetric catalytic hydrosilation provides an attractive solution to the chemoselective hydration of olefins and the reduction of ketones. This proposal is directed at developing new chiral catlysts for asymmetric catalytic hydrosilation. A mechanistic rationalization is offered which suggests that certain readily available substrates will generate high optical yields by an intramolecular process. The strategy employs familiar concepts of discrimination by preferred cyclic conformations in the enantioseleetive transition sites. The products of hydrosilation are readily converted into optically active 1,4-, 1,3 and 1,2-diols. These diols are key starting materials in the synthesis of macrolide and ionophore antibioties. The proposal is also directed at an important methodological issue. This concerns the problem of selecting the correct catalyst and substrate which will give high optical yields. For this purpose, it is proposed to investigate the mechanism of the reaction in order to determine the origins of the enantioselection. Such studies will provide a basis for the design of catalysts for other transformations.