Understanding the relative acyl-transfer reactivity of oxoesters and thioesters: computational analysis of transition state delocalization effects.
Understanding the relative acyl-transfer reactivity of oxoesters and thioesters: computational analysis of transition state delocalization effects.
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DOI：
10.1021/ja010726a
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发表时间：
2001-10
影响因子：
15
通讯作者：
W. Yang;D. Drueckhammer
中科院分区：
文献类型：
--
作者：
W. Yang;D. Drueckhammer
计算研究进行了努力，以了解在亲核酰基转移反应中的氧代酯和硫代酯的相对反应性。建立了乙酸甲酯和硫代乙酸甲酯与氢氧化物、氨和氰乙酸甲酯负碳离子反应的过渡态模型。基于这些模型的量子力学计算再现了实验观察，即氧代酯和硫代酯对氢氧化物具有相似的反应性，而硫代酯对胺和碳负离子亲核试剂的反应性分别比氧代酯高约100倍和至少2000倍。NBO分析阐明了电子离域在反应物和过渡态稳定中的作用。这些计算表明，氧代酯和硫代酯在与氢氧化物反应中从反应物到过渡态的离域能损失相似，而氧代酯在与其他亲核试剂反应中的离域能损失明显更大。与氢氧化物和氨反应的过渡态的键旋转分析为p（X）--> sigma（C-Nu）相互作用（X分别为氧代酯或硫代酯的O或S，Nu =亲核试剂）在控制氧代酯和硫代酯在亲核酰基取代中的反应性中的重要作用提供了支持。
Computational studies were performed in an effort to understand the relative reactivity of oxoesters and thioesters in nucleophilic acyl transfer reactions. Transition state models were developed for the reactions of methyl acetate and methyl thioacetate with hydroxide, ammonia, and methylcyanoacetate carbanion. Quantum mechanical calculations based on these models reproduced experimental observations that oxoesters and thioesters have similar reactivity toward hydroxide while thioesters are about 100-fold and at least 2000-fold more reactive than oxoesters toward amine and carbanion nucleophiles, respectively. NBO analysis was performed to elucidate the role of electron delocalization in reactant and transition state stabilization. These calculations indicate similar losses of delocalization energy for the oxoester and thioester in going from the reactants to the transition state in reaction with hydroxide while the loss of delocalization energy is significantly greater for the oxoester in reactions with the other nucleophiles. Bond rotational analysis of the transition states for the reactions with hydroxide and ammonia provide support for an important role of the p(X) --> sigma(C-Nu) interaction (X = O or S of the oxoester or thioester respectively, Nu = nucleophile) in governing the reactivity of oxoesters and thioesters in nucleophilic acyl substitution.