Mechanism of amido-thiourea catalyzed enantioselective imine hydrocyanation: transition state stabilization via multiple non-covalent interactions.
Mechanism of amido-thiourea catalyzed enantioselective imine hydrocyanation: transition state stabilization via multiple non-covalent interactions.
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DOI：
10.1021/ja9058958
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发表时间：
2009-10-28
影响因子：
15
通讯作者：
Jacobsen, Eric N.
中科院分区：
文献类型：
--
作者：
Zuend, Stephan J.;Jacobsen, Eric N.
对氨基硫脲促进亚胺氢氰化反应的实验和计算研究揭示了一种新的、意想不到的催化机制。与先前在相关系统中提出的硫脲直接激活亚胺不同，数据与催化剂促进质子从异氰化氢转移到亚胺产生非对映体的亚胺/氰化物离子对的机制一致，这些离子对通过多种非共价相互作用与催化剂结合；这些离子对坍塌形成对映体α-氨基腈产物。8种不同催化剂诱导的实验对映选择性和计算对映选择性之间存在统计学上显著的相关性（P≪0.01），这一机制建议得到了支持。计算模型揭示了对映体选择性的基础，涉及底物和催化剂之间的多种稳定和不稳定相互作用，包括硫脲-氰化物和酰胺-胺相互作用。
An experimental and computational investigation of amido-thiourea promoted imine hydrocyanation has revealed a new and unexpected mechanism of catalysis. Rather than direct activation of the imine by the thiourea, as had been proposed previously in related systems, the data are consistent with a mechanism involving catalyst-promoted proton transfer from hydrogen isocyanide to imine to generate diastereomeric iminium/cyanide ion pairs that are bound to catalyst through multiple non-covalent interactions; these ion pairs collapse to form the enantiomeric α-aminonitrile products. This mechanistic proposal is supported by the observation of a statistically significant correlation between experimental and calculated enantioselectivities induced by eight different catalysts (P ≪ 0.01). The computed models reveal a basis for enantioselectivity that involves multiple stabilizing and destabilizing interactions between substrate and catalyst, including thiourea-cyanide and amide-iminium interactions.
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