Factors Influencing 1,4-Asymmetric Induction during Indium-Promoted Coupling of Oxygen-Substituted Allylic Bromides to Aldehydes in Aqueous Solution
作者:Leo A. Paquette、George D. Bennett、Adnan Chhatriwalla、Methvin B. Isaac
DOI:10.1021/jo970158a
日期:1997.5.1
operation of chelation effects during oxidative addition of the metal into the carbon-bromine bond, but not during the coupling stage. Once the aldehyde enters into the coordination sphere of the indium, internal chelation to the proximal oxygen is disrupted and conformational restrictions are released. These effects, in combination with the absence of a powerful steric control element in the latter
描述了在水性条件下一系列3-取代的3-氧-1-溴-2-亚甲基丙烷的制备和铟促进的醛加成反应。(叔丁基二甲基甲硅烷基)氧基衍生物4a-d是这组试剂中最非对映选择性的,导致syn-1,4-不对称诱导的水平为87-99%。有趣的是,当氧取代基的空间体积减少时,如在羟基和甲氧基衍生物中一样,顺式立体选择性被侵蚀并且反应进行得更快。π面动速差的下降是由于动力学加速引起的,这归因于在金属氧化成碳-溴键的过程中螯合效应的作用,而不是在耦合阶段。醛进入铟的配位区后,内部氧与近端氧的螯合被破坏,构象限制被释放。这些效果,在后面的例子中,加上缺少强大的空间控制元件,可以通过顺和反过渡态进行竞争性传递。