Pre-activation based stereoselective glycosylations: Stereochemical control by additives and solvent
作者:Gilbert Wasonga、YouLin Zeng、XueFei Huang
DOI:10.1007/s11426-010-4186-6
日期:2011.1
several triflate salt additives did not have major effects, the amount of AgOTf was found to significantly impact the reaction outcome. Excess AgOTf led to lower stereochemical control presumably due to its coordination with the glycosyl triflate intermediate and a more S(N)1 like reaction pathway. In contrast, the stereoselectivity could be directed by reaction solvents, with diethyl ether favoring the
立体化学控制是碳水化合物合成中的一个重要问题。已证明在基于预活化的反应条件下,在 2-O 上具有参与酰基保护基团的糖基供体能够可靠地产生 1,2-反式糖苷。在这项工作中,使用供体检查添加剂和反应溶剂对立体选择性的影响,而没有参与 2-O 上的保护基团。虽然几种三氟甲磺酸盐添加剂没有重大影响,但发现 AgOTf 的量会显着影响反应结果。过量的 AgOTf 导致较低的立体化学控制,大概是由于它与糖基三氟甲磺酸酯中间体和更像 S(N)1 的反应途径的协调。相反,立体选择性可以由反应溶剂来指导,乙醚有利于形成 α 糖苷,而二氯甲烷则有利于形成 β 异构体。立体化学依赖于反应溶剂的趋势适用于各种构建模块,包括选择性形成 β-甘露糖苷。