Scope and Mechanism of the Ruthenium-Catalyzed sp3 C–H Coupling Reaction of 2-Alkylindoles with Enones for the Synthesis of Carbazole Derivatives

IF 2.5 3区 化学 Q2 CHEMISTRY, INORGANIC & NUCLEAR
Krishna Prasad Gnyawali, Mina Son, Donghun Hwang, Nuwan Pannilawithana, Mu-Hyun Baik* and Chae S. Yi*, 
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Abstract

The catalytic system consisting of a cationic Ru–H complex 1 and 3,4,5,6-tetrachloro-1,2-benzoquinone (L1) was found to be highly effective for the dehydrative sp3 C–H coupling reaction of 2-alkyl substituted indoles with enones to form 2,4-disubstituted carbazole products. The analogous coupling reaction of 2-alkylindoles with linear enones bearing the cyclic olefinic group afforded tetracyclic carbazole products. A normal deuterium kinetic isotope effect was measured from the coupling reaction of 1,2-dimethylindole versus 1-methyl-2-(methyl-d3)indole with (E)-3-penten-2-one (kH/kD = 2.5). The Hammett plot was constructed from the reaction of para-substituted indoles 5-X-1,2-dimethylindole (X = OMe, Me, H, F, and Cl) with 4-phenyl-3-buten-2-one (ρ = −1.6 ± 0.2). The density functional theory (DFT) calculations were performed to obtain a complete energy profile for the coupling reaction. The combined experimental and DFT computational data revealed a detailed mechanistic path that features an initial coupling of indole and enone substrates, the turnover-limiting heterolytic sp3 C–H activation step, and the subsequent cyclization and dehydration steps. The catalytic method provides an efficient synthesis of carbazole derivatives from the dehydrative sp3 C–H coupling reaction of readily available indole with enone substrates without employing any reactive reagents or forming wasteful byproducts.

Abstract Image

钌催化2-烷基醇与烯酮sp3 C-H偶联反应合成咔唑衍生物的范围和机理
由阳离子Ru-H配合物1和3,4,5,6-四氯-1,2-苯醌(L1)组成的催化体系对2-烷基取代吲哚与烯酮的脱水sp3 C-H偶联反应生成2,4-二取代咔唑产品非常有效。2-烷基啉与含环烯烃基团的线性烯酮的类似偶联反应产生了四环咔唑产物。通过1,2-二甲基吲哚与1-甲基-2-(甲基-d3)吲哚与(E)-3-戊烯-2-酮(kH/kD = 2.5)的偶联反应,测量了正常的氘动力学同位素效应。通过对取代吲哚5-X-1,2-二甲基吲哚(X = OMe, Me, H, F, Cl)与4-苯基-3-丁烯-2-酮(ρ =−1.6±0.2)的反应建立了Hammett图。利用密度泛函理论(DFT)计算得到了耦合反应的完整能量分布。结合实验和DFT计算数据揭示了一个详细的机制路径,包括吲哚和烯酮底物的初始耦合,限制翻转的sp3 C-H异裂解激活步骤,以及随后的环化和脱水步骤。该催化方法提供了一种由容易获得的吲哚与烯酮底物的脱水sp3 C-H偶联反应有效合成咔唑衍生物的方法,而不使用任何反应试剂或形成浪费的副产物。
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来源期刊
Organometallics
Organometallics 化学-无机化学与核化学
CiteScore
5.60
自引率
7.10%
发文量
382
审稿时长
1.7 months
期刊介绍: Organometallics is the flagship journal of organometallic chemistry and records progress in one of the most active fields of science, bridging organic and inorganic chemistry. The journal publishes Articles, Communications, Reviews, and Tutorials (instructional overviews) that depict research on the synthesis, structure, bonding, chemical reactivity, and reaction mechanisms for a variety of applications, including catalyst design and catalytic processes; main-group, transition-metal, and lanthanide and actinide metal chemistry; synthetic aspects of polymer science and materials science; and bioorganometallic chemistry.
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