1,3-Chlorine Shift to a Vinyl Cation: A Combined Experimental and Theoretical Investigation of the E-Selective Gold(I)-Catalyzed Dimerization of Chloroacetylenes.
1,3-Chlorine Shift to a Vinyl Cation: A Combined Experimental and Theoretical Investigation of the E-Selective Gold(I)-Catalyzed Dimerization of Chloroacetylenes.
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DOI：
10.1021/jacs.8b11501
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发表时间：
2019-01
影响因子：
15
通讯作者：
Mathis Kreuzahler;Alyssa Daniels;C. Wölper;Gebhard Haberhauer
中科院分区：
文献类型：
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作者：
Mathis Kreuzahler;Alyssa Daniels;C. Wölper;Gebhard Haberhauer
末端乙炔的金属催化二聚反应在文献中是众所周知的。然而，仅描述了卤素取代的乙炔的二聚化的几个实例。后一种金属催化二聚反应的产物是支化的头-尾烯炔。相应的线性头对头烯炔的形成尚未报道。在此，我们通过量子化学方法和实验证明，氯芳基乙炔的头对头二聚可以通过单金催化实现。在优化的条件下，观察到起始材料的清洁和完全转化，并且获得高达75%NMR产率的二聚产物。二聚反应的机理研究表明，支化的头-尾乙烯基阳离子比相应的线性头-头阳离子在能量上更稳定。然而，后者可以通过不寻常的1，3-氯位移重排，导致高度立体选择性地形成反式产物，其对应于头对头E-烯炔的金络合物。这种重排的活化势垒非常低（约为1000）。2kcal/mol）。由于单金催化的二聚反应可以在制备规模中进行，因此反式-1，2-二氯烯炔的这种简单合成使得氯芳基乙炔的金（I）催化的头对头二聚反应成为一种有吸引力的方法，从而获得更复杂的共轭烯炔体系及其同系物。
Metal-catalyzed dimerization reactions of terminal acetylenes are well known in the literature. However, only a few examples of the dimerization of halogen-substituted acetylenes are described. The products of the latter metal-catalyzed dimerization are the branched head-to-tail enynes. The formation of the corresponding linear head-to-head enynes has not been reported yet. Herein, we demonstrate by means of quantum chemical methods and experiments that the head-to-head dimerization of chloroarylacetylenes can be achieved via mono gold catalysis. Under the optimized conditions, a clean and complete conversion of the starting materials is observed and the dimeric products are obtained up to 75% NMR yield. A mechanistic investigation of the dimerization reaction reveals that the branched head-to-tail vinyl cation is energetically more stable than the corresponding linear head-to-head cation. However, the latter can rearrange by an unusual 1,3-chlorine shift, resulting in the highly stereoselective formation of the trans product, which corresponds to the gold complex of the head-to-head E-enyne. The activation barrier for this rearrangement is extremely low (ca. 2 kcal/mol). As the mono gold-catalyzed dimerization can be conducted in a preparative scale, this simple synthesis of trans-1,2-dichloroenynes makes the gold(I)-catalyzed head-to-head dimerization of chloroarylacetylenes an attractive method en route to more complex conjugated enyne systems and their congeners.