Stereoselective C-glycosylation reactions of ribose derivatives:: Electronic effects of five-membered ring oxocarbenium ions
Stereoselective C-glycosylation reactions of ribose derivatives:: Electronic effects of five-membered ring oxocarbenium ions
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DOI：
10.1021/ja0524043
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发表时间：
2005-08-10
影响因子：
15
通讯作者：
Woerpel, KA
中科院分区：
文献类型：
--
作者：
Larsen, CH;Ridgway, BH;Woerpel, KA
通过对18个在C-2、C-3和C-4取代位置不同的核糖类似物的立体选择性反应，确定了控制核糖衍生物高选择性c -糖基化的因素。中间氧碳离子的最低能量构象显示C-3烷氧基在假轴取向，以最大限度地提高静电效应。在较小程度上，C-2取代基倾向于赝赤道位置，而C-4上的烷基对构象偏好的影响较小。在所有情况下，产物都是通过在最低能量的构象上的立体电子优先内攻而形成的。
The factors controlling the highly a-selective C-glycosylation of ribose derivatives were determined by examining the stereoselective reactions of 18 ribose analogues differing in substitution at C-2, C-3, and C-4. The lowest energy conformers of the intermediate oxocarbenium ions display the C-3 alkoxy group in a pseudoaxial orientation to maximize electrostatic effects. To a lesser extent, the C-2 substituent prefers a pseudoequatorial position, and the alkyl group at C-4 has little influence on conformational preferences. In all cases, the product was formed by stereoelectronically preferred inside attack on the lowest energy conformer.