Development of a Highly β-Selective Ribosylation Reaction without Using Neighboring Group Participation: Total Synthesis of (+)-Caprazol, a Core Structure of Caprazamycins
作者:Shinpei Hirano、Satoshi Ichikawa、Akira Matsuda
DOI:10.1021/jo701699h
日期:2007.12.1
(+)-caprazol are described. The key elements of our approach include the early stage introduction of the aminoribose in a highly β-selective manner, using the steric hindrance in the transition state and the construction of the diazepanone by a modified intramolecular reductive amination. The 5‘-C-glycyluridine derivative 9, which was prepared stereoselectively via Sharpless asymmetric aminohydroxylation,
描述了(+)-辣椒碱的全合成的全部细节。我们方法的关键要素包括:以过渡型空间位阻,以高度β-选择性的方式早期引入氨基核糖,以及通过修饰的分子内还原胺化作用构建二氮杂酮。经由Sharpless不对称氨基羟基化立体选择性地制备的5'- C-甘氨酰尿苷衍生物9被2,3- O-亚烷基核呋喃糖基供体核糖化。揭示了增加缩醛单元的烷基取代基的尺寸导致改善了端基异构体位置的立体选择性,以及所需的核糖苷21b(1′′-β)和22b。当使用具有更空间位阻的3-亚戊基的核糖基氟化物16时,以80%的收率获得(1′′-α)(21b / 22b= 24.0 / 1)。还讨论了核糖基化的立体选择性的起源。使用模型醛37优化了二氮杂酮系统的构建,并通过包括催化加氢然后进行氢化物还原的两步反应序列,以88%的收率获得了所需的二氮杂酮38。将该方法应用于醛44可成功获得二氮杂酮衍生物45和46。,其官能团操作完成了(+)-卡巴唑的全部合成。