Unlocking a self-catalytic cycle in a copper-catalyzed aerobic oxidative coupling/cyclization reaction

Jianming Liu; Xiaopei Wang; Zhiyue Wang; Yan Yang; Qinghu Tang; Hongchi Liu; Hanmin Huang

doi:10.1016/j.isci.2022.103906

Unlocking a self-catalytic cycle in a copper-catalyzed aerobic oxidative coupling/cyclization reaction

iScience. 2022 Feb 12;25(3):103906. doi: 10.1016/j.isci.2022.103906. eCollection 2022 Mar 18.

Authors

Jianming Liu¹, Xiaopei Wang¹, Zhiyue Wang¹, Yan Yang¹, Qinghu Tang¹, Hongchi Liu², Hanmin Huang²

Affiliations

¹ Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, Henan 453007, P. R. China.
² Hefei National Laboratory for Physical Sciences at the Microscale and Department of Chemistry, Center for Excellence in Molecular Synthesis of CAS, University of Science and Technology of China, Hefei 230026, P. R. China.

Abstract

Presented here is a copper-catalyzed, aerobic oxidative C-H/C-H cyclization reaction, which occurs by cleaving the C-H and N-H bonds of 3-phenylindoles. A broad range of 3-phenylindoles can be well tolerated to produce the indole-containing polycyclic aromatic hydrocarbons (PAH) in good to excellent yields. An evaluation of the reaction mechanism is enabled by the isolation of the di- and tri-indole intermediates, highlighting the role of the substrate for this catalytic reaction. The results of these controlled experiments and kinetic studies provide solid experimental support for a self-catalysis reaction, which has rarely been observed in oxidative C-H activation reactions. Additional mechanistic studies indicate that the substrate for this reaction accelerates by the following mechanism: The substrate combines with the Cu catalyst to transform the less active di-indole intermediate into a tri-indole intermediate. This intermediate is quickly converted into the desired product along with regeneration of the substrate copper complex.

Keywords: Catalysis; Chemical engineering; Chemistry.