我们在此证明,应变和空间位阻质子化 2,4,6-三叔丁基吡啶鎓 (TTBPy) 四氟硼酸盐(一种结晶的、工作台稳定的盐)可作为温和且高效的有机催化剂,用于糖基三氯乙酰亚胺酯的 S N 2 型置换α-和β-糖苷的立体选择性合成。位阻吡啶鎓阳离子和四氟硼酸根阴离子之间的紧张离子对相互作用给离子注入了不寻常的反应性,从而导致独特的阴离子辅助醇的活化。醇的这种温和活化促进了糖基α-三氯乙酰亚胺酯以高度非对映选择性的方式发生S N 2 型置换成β-糖苷。这些独特的相互作用是基于广泛的红外和1 H、 19 F、 11 B NMR 研究和理论研究而建立的。
Generally applicable and stereoselective formation of 1,2-cis-glycopyranosidic linkage remains a long sought after yet unmet goal in carbohydrate chemistry. This work advances a strategy to this challenge via stereoinversion at the anomeric position of 1,2-trans glycosylesterdonors. This SN2 glycosylation is enabled under gold catalysis by an oxazole-based directing group optimally tethered to a
1,2-顺式-吡喃糖苷键的普遍适用和立体选择性形成仍然是碳水化合物化学中长期追求但尚未实现的目标。这项工作通过在 1,2-反式糖基酯供体的异头位置上的立体倒置推进了应对这一挑战的策略。这种 S N 2 糖基化是在金催化下通过以恶唑为基础的导向基团实现的,该导向基团最佳地束缚在离去基团上,并在温和的催化条件下以大多数优异的产率和良好的选择性实现。该策略也适用于寡糖的合成。
Establishment of Guidelines for the Control of Glycosylation Reactions and Intermediates by Quantitative Assessment of Reactivity
Stereocontrolled chemical glycosylation remains a major challenge despite vast efforts reported over many decades and so far still mainly relies on trial and error. Now it is shown that the relative reactivity value (RRV) of thioglycosides is an indicator for revealing stereoselectivities according to four types of acceptors. Mechanistic studies show that the reaction is dominated by two distinct intermediates:
Generation of Alkoxycarbenium Ion Pools from Thioacetals and Applications to Glycosylation Chemistry
作者:Shinkiti Suzuki、Kouichi Matsumoto、Kohsuke Kawamura、Seiji Suga、Jun-ichi Yoshida
DOI:10.1021/ol048524h
日期:2004.10.1
[reaction: see text] Alkoxycarbenium ions have been generated and accumulated as "cation pools" by the low-temperature electrochemical oxidation of alpha-phenylthioethers. Although an unsuccessful attempt to accumulate glycosyl cations was made, a one-pot method for electrochemicalglycosylation, which involves anodic oxidation of thioglycosides to generate glycosyl cation equivalents followed by their reactions
electrochemical reactor that accomplishes electrolysis within a few seconds was developed, enabling flash generation of short-lived carbocations and trapping reaction with nucleophiles before they decompose. The present methodology was applied to highly reactive oxocarbenium ions, N-acyliminium ions, glycosyl cations, and the Ferrier cations. Moreover, continuous and flash synthesis of a pharmaceutical