Mechanism of thio acid/azide amidation
Mechanism of thio acid/azide amidation
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DOI：
10.1021/ja057533y
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发表时间：
2006-05-03
影响因子：
15
通讯作者：
Williams, LJ
中科院分区：
文献类型：
--
作者：
Kolakowski, RV;Shangguan, N;Williams, LJ
结合实验和计算机制的研究，从硫代酸和叠氮化物酰胺形成描述。数据支持两种不同的机制途径依赖于叠氮化物组分的电子特性。相对富电子的叠氮化物通过阴离子加速[3+2]环加成与硫代羧酸盐进行双分子偶联，得到硫代三唑啉。高度电性差的叠氮化物通过叠氮化物末端氮与硫代羧酸盐的硫的双分子结合而偶联成线性加合物。这种中间体的环化得到硫三唑啉。发现中性噻唑啉中间体通过反[3+2]环加成分解为酰胺。计算分析（DFT, 6-31 +G(d)）确定了两类叠氮化物与硫代酸进行[3+2]环加成得到硫代三唑啉中间体的途径，尽管这些途径的能量高于硫代羧酸酰胺化。这些研究还表明，贫电子叠氮化物的反应谱可归因于先前的捕获机制，然后是分子内酰化。
A combined experimental and computational mechanistic study of amide formation from thio acids and azides is described. The data support two distinct mechanistic pathways dependent on the electronic character of the azide component. Relatively electron-rich azides undergo bimolecular coupling with thiocarboxylates via an anion-accelerated [3+2] cycloaddition to give a thiatriazoline. Highly electronpoor azides couple via bimolecular union of the terminal nitrogen of the azide with sulfur of the thiocarboxylate to give a linear adduct. Cyclization of this intermediate gives a thiatriazoline. Decomposition to amide is found to proceed via retro-[3+2] cycloaddition of the neutral thiatriazoline intermediates. Computational analysis (DFT, 6-31 +G(d)) identified pathways by which both classes of azide undergo [3+2] cycloaddition with thio acid to give thiatriazoline intermediates, although these paths are higher in energy than the thiocarboxylate amidations. These studies also establish that the reaction profile of electron-poor azides is attributable to a prior capture mechanism followed by intramolecular acylation.