Formation and stability of oxocarbenium ions from glycosides
Formation and stability of oxocarbenium ions from glycosides
复制标题
DOI：
10.1002/jms.880
复制
发表时间：
2005-08-01
影响因子：
2.3
通讯作者：
Sandlers, Y
中科院分区：
文献类型：
--
作者：
Denekamp, C;Sandlers, Y
研究了氧羰基中间体在气相中形成过程中的结构效应、保护基效应和离去基效应。研究发现，尽管氧羰基具有吸电子的特性，但通过邻近基团参与保护与阳离子中心相互作用的基团，氧羰基阳离子具有显著的稳定性。另一方面，空灵的保护基团不促进氧羰基中间体的形成。实验结果得到了DFT计算的支持，DFT计算表明，靠近阳离子中心的基团的稳定顺序如下：RCO > SiR3 > R，其中R为烷基。这表明通常提出的sn1样反应机制并不总是有效的。在一系列硫代氨基葡萄糖苷中也检测到适度的离去基效应。版权所有(c) 2005 John Wiley & Sons, Ltd。
Structural, protecting group and leaving group effects in the formation of oxocarbenium intermediates were studied in the gas phase. It is found that significant stabilization of oxocarbenium cations is achieved by protecting groups that interact with the cationic center via neighboring group participation despite the electron-withdrawing character of these moieties. On the other hand, ethereal protecting groups do not facilitate the formation of oxocarbenium intermediates. The experimental findings are supported by DFT calculations that show the following order of stabilization by the group adjacent to the cationic center: RCO > SiR3 > R, where R is an alkyl group. This indicates that the SN1-like mechanism that is commonly proposed for this reaction is not always valid. Moderate leaving group effect is also detected in a series of thioaryl glucopyranosides. Copyright (c) 2005 John Wiley & Sons, Ltd.