Probing the Mechanism of Sulfoxide-Catalyzed Hemiacetal Activation in Dehydrative Glycosylation
作者:Timothy A. Boebel、David Y. Gin
DOI:10.1021/jo050294c
日期:2005.7.1
nucleophile and subsequent glycosidic bond formation. Successful determination of the proportion of 18O incorporation in 10 as a function of its formation, via the technique of dynamic monitoring of 13C−16/18O isotopic chemical shift perturbations, provides strong evidence that hemiacetal activation proceeds through initial nucleophilic addition of the hemiacetal hydroxyl to the S(IV)-center of putative
亚砜-共价催化的概念已经建立在通用的半缩醛羟基活化/取代反应的背景下,以形成异头键。侧重于半缩醛活化过程的机理研究表明,这种转化是在磺酸酐和除酸剂的存在下,通过糖基磺酸盐物种(10)的中介进行的,该过程在添加外部亲核试剂之前处于静止状态以及随后的糖苷键形成。通过动态监测13 C- 16 / 18技术成功确定10中18 O的掺入比例作为其形成的函数O同位素化学位移扰动,提供了有力的证据表明,半缩醛活化是通过将半缩醛羟基最初亲核加成到假定的磺酸sulf 6的S(IV)中心而进行的。通过独立合成,结构验证,和1 H NMR检测糖基氧ulf 11在亚砜3转化为糖基磺酸盐10的亚砜催化转化过程中得到了进一步的证实。