Influence of alkoxy groups on rates of acetal hydrolysis and tosylate solvolysis: electrostatic stabilization of developing oxocarbenium ion intermediates and neighboring-group participation to form oxonium ions.
Influence of alkoxy groups on rates of acetal hydrolysis and tosylate solvolysis: electrostatic stabilization of developing oxocarbenium ion intermediates and neighboring-group participation to form oxonium ions.
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DOI：
10.1021/acs.joc.5b00338
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发表时间：
2015-04
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影响因子：
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通讯作者：
Angie Garcia;Douglas A. L. Otte;Walter A. Salamant;Jillian R. Sanzone;K. Woerpel
中科院分区：
文献类型：
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作者：
Angie Garcia;Douglas A. L. Otte;Walter A. Salamant;Jillian R. Sanzone;K. Woerpel
4-烷氧基取代的缩醛的水解被加速了约20倍相比，空间上相当的基板，不具有烷氧基。速率加速度是最大的两个功能团是由一个灵活的循环系绳连接。当控制诱导去稳定化时，烷氧基可以加速缩醛水解高达200倍。其中烷氧基通过五元环与缩醛基团连接的底物与其中烷氧基通过八元环与缩醛基团连接的底物之间的缩醛水解速率的差异小于100倍，表明未形成稠环中间体。相比之下，结构相关的甲苯磺酸酯的溶剂分解速率的差异在五元环系列和八元环系列之间接近10（6）倍。这一观察结果暗示邻基参与甲苯磺酸酯的溶剂分解，但不参与缩醛的水解。通过在缩醛碳原子处积累正电荷的中间体的静电稳定化，更好地解释了烷氧基对缩醛水解的加速。
The hydrolysis of 4-alkoxy-substituted acetals was accelerated by about 20-fold compared to that of sterically comparable substrates that do not have an alkoxy group. Rate accelerations are largest when the two functional groups are linked by a flexible cyclic tether. When controlled for the inductive destabilization, an alkoxy group can accelerate acetal hydrolysis by up to 200-fold. The difference in rates of acetal hydrolysis between a substrate where the alkoxy group was tethered to the acetal group by a five-membered ring compared to one where it was tethered by an eight-membered ring was less than 100-fold, suggesting that fused-ring intermediates were not formed. By comparison, the difference in rates of solvolysis of structurally related tosylates were nearly 10(6)-fold between the five- and eight-membered ring series. This observation implicates neighboring-group participation in the solvolysis of tosylates but not in the hydrolysis of acetals. The acceleration of acetal hydrolysis by an alkoxy group is better explained by electrostatic stabilization of intermediates that accumulate positive charge at the acetal carbon atom.