Functionalized Cyclopentadienyl Ligands and Their Substituent Effects on a Rhodium(III)‐Catalyzed Oxidative [4+2] Annulation of Indole‐ and Pyrrole‐1‐Carboxamides with Alkynes,Asian Journal of Organic Chemistry

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Functionalized Cyclopentadienyl Ligands and Their Substituent Effects on a Rhodium(III)‐Catalyzed Oxidative [4+2] Annulation of Indole‐ and Pyrrole‐1‐Carboxamides with Alkynes
Asian Journal of Organic Chemistry ( IF 2.8 ) Pub Date : 2018-06-08 , DOI: 10.1002/ajoc.201800262
Takayuki Yamada ₁ , Yu Shibata ₁ , Ken Tanaka ₁

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The effect of substituents on carbamoylmethyl‐cyclopentadienyl (Cp^A) ligands on the neutral rhodium(III)‐catalyzed oxidative [4+2] annulation of indole‐ and pyrrole‐1‐carboxamides with alkynes, in which the C−H bond cleavage is the partially rate‐limiting step, was investigated. As a result, in the reactions with terminal alkynes, a rhodium(III) complex with a dimethyl‐substituted Cp^A ligand (Cp^A3) showed high catalytic activity and improved the regioselectivity as compared to a commercially available Cp*Rh^III complex. On the other hand, in reactions with internal alkynes, a rhodium(III) complex with a diphenyl‐substituted Cp^A ligand (Cp^A1 or Cp^A2) showed high catalytic activity, which is comparable to the activity of the Cp*Rh^III complex. Interestingly, a rhodium(III) complex with an electron‐deficient di(ethoxycarbonyl)‐substituted Cp ligand (Cp^E) that shows high catalytic activity toward the annulation of benzamides with internal alkynes, in which the C−H cleavage is rate‐limiting, showed low catalytic activity toward the reactions with both terminal and internal alkynes. The ligand effects above provide important guidelines for the application of our Cp^A and Cp^E ligands to the rhodium(III)‐catalyzed C−H bond functionalization reactions.

中文翻译：

功能化的环戊二烯基配体及其在铑（III）催化的吲哚和吡咯-1-羧酰胺与炔烃的氧化[4 + 2]环化反应中的取代作用

取代基对中性铑（III）催化的炔烃和吡咯-1-羧酰胺与炔烃的中性铑（III）催化氧化[4 + 2]环合反应上的氨基甲酰基甲基-环戊二烯基（Cp ^A）配体的影响研究了部分限速步骤。结果，在与末端炔烃的反应中，与市售Cp * Rh ^III配合物相比，具有二甲基取代的Cp ^A配体（Cp ^A3）的铑（III）配合物显示出高催化活性并改善了区域选择性。另一方面，在与内部炔烃反应时，铑（III）与二苯基取代的Cp ^A配体（Cp ^A1或Cp ^A2）显示出高催化活性，与Cp * Rh ^III配合物的活性相当。有趣的是，具有缺电子的二（乙氧基羰基）取代的Cp配体（Cp ^E）的铑（III）配合物对苯甲酰胺与内部炔烃的环合显示出高催化活性，其中CH裂解是限速的，对末端和内部炔烃的反应均显示出较低的催化活性。上面的配体效应为将我们的Cp ^A和Cp ^E配体应用到铑（III）催化的C-H键官能化反应中提供了重要的指导。

更新日期：2018-06-08

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