Enantioselective Alkynylbenzaldehyde Cyclizations Catalyzed by Chiral Gold(I) Acyclic Diaminocarbene Complexes Containing Weak Au-Arene Interactions
Enantioselective Alkynylbenzaldehyde Cyclizations Catalyzed by Chiral Gold(I) Acyclic Diaminocarbene Complexes Containing Weak Au-Arene Interactions
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DOI：
10.1002/anie.201107789
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发表时间：
2012-01-01
影响因子：
16.6
通讯作者：
Slaughter, LeGrande M.
中科院分区：
文献类型：
--
作者：
Handa, Sachin;Slaughter, LeGrande M.
由于AUI具有激活各种不饱和键进行亲核攻击的能力，金(I)催化已成为合成复杂有机结构的有力工具。[1]在开发对映体选择性催化剂的努力中，AUI的线性配位几何构型提出了挑战，因为手性配体取代基的距离较远，底物无法采用有利于不对称诱导的螯合结合模式。然而，金催化剂在许多反应中都达到了很高的对映体选择性。有证据表明，配体的二次相互作用有助于克服在AUI中心实现手性环境的固有困难。[3]不对称金催化的开创性例子利用侧基和底物之间的静电吸引来实现高度对映选择性的Aldol反应。[4]对于手性联芳基双膦(目前最成功的AUI手性催化剂设计)的双(金)络合物，已提出膦取代基的π-π相互作用在金属周围创建手性口袋中起关键作用。[5]在一篇有趣的报告中，手性亚磷酰胺配体的富电子芳基与AUI的相互作用极大地提高了底物结合部位的手性。[6]本文报道了AUI与手性卡宾配体上的缺电子芳基的二次相互作用与串联加成/环异构化反应中的高对映选择性催化有关。这些结果提示了一种新的手性催化剂设计基元，它可以使AUI催化剂在对映选择性应用方面取得进一步的进展。环二氨基卡宾配体(ADC)，也被称为氮无环卡宾(NAC)，在对映选择性催化方面比更常见的N-杂环卡宾(NHC)具有潜在的优势，[8]因为它们的大NCN角(116-1218)可以将手性取代基放置在更接近金属的位置。然而，尽管人们对手性ADC配体在催化中的应用越来越感兴趣，但几乎没有出现手性ADC配体的例子。
Catalysis with gold (I) has emerged as a powerful tool for the synthesis of complex organic structures, owing to the ability of AuI to activate a variety of unsaturated bonds toward nucleophilic attack.[1] In efforts to develop enantioselective catalysts, the linear coordination geometry of AuI presents challenges because of the remoteness of chiral ligand substituents and the inability of substrates to adopt a chelate binding mode that favors asymmetric induction. Nevertheless, high enantioselectivities have been achieved with gold catalysts in an impressive number of reactions.[2] In a few cases, there is evidence that secondary interactions of the ligand help to overcome the inherent difficulty of achieving a chiral environment at a AuI center.[3] The seminal example of asymmetric gold catalysis utilized the electrostatic attraction between a pendant ammonium group and the substrate to achieve highly enantioselective aldol reactions.[4] For bis (gold) complexes of chiral biaryl diphosphines—currently the most successful chiral catalyst design for AuI—it has been proposed that π–π interactions of the phosphine substituents play a key role in creating a chiral pocket around the metals.[5] In one intriguing report, interactions of electron-rich aryl groups of chiral phosphoramidite ligands with AuI were found to greatly enhance the chirality of the substrate binding site.[6] Herein we report that secondary interactions of AuI with electron-deficient aryl substituents on chiral carbene ligands are associated with highly enantioselective catalysis in a tandem addition/cycloisomerization reaction. These results suggest a new chiral catalyst design motif that could enable further advances in enantioselective applications of AuI catalysts.Acyclic diaminocarbene ligands (ADC),[7] also known as nitrogen acyclic carbenes (NAC), are potentially advantageous over the more familiar N-heterocyclic carbenes (NHC) for enantioselective catalysis,[8] because their wide NCN angles (116–1218) can place chiral substituents closer to the metal. However, few examples of chiral ADC ligands have appeared despite growing interest in the use of ADC ligands in catalysis.[9, 10] Significant asymmetric induction has only