Aerobic Intramolecular Oxidative Coupling Using Heterogeneous Catalyst for Synthesis of <i>N</i>-Substituted 2,3,6,7-Tetramethoxycarbazoles

Abstract

A heterogeneous metal catalyst enabled the intramolecular oxidative coupling of diarylamines to form carbazoles with molecular oxygen as the sole oxidant. Rh/C had efficient catalytic activity and allowed the catalyst loading to be reduced to 0.1 mol% while maintaining excellent yields of carbazoles. This reaction is operationally simple in an open-to-air setup, and provides a green and atom-economical process for an efficient synthetic approach to N-substituted carbazoles.

Catalytic and Aerobic Oxidative Biaryl Coupling of Anilines Using a Recyclable Heterogeneous Catalyst for Synthesis of Benzidines and Bicarbazoles

“…In 2017, Knölker described an iron-catalyzed oxidative homocoupling of diarylamines utilizing an iron­(II)-hexadecafluorophthalocyanine (FeF 16 Pc)/MsOH/air system (Scheme A) . Recently, we reported the intramolecular biaryl coupling of diarylamines under mild aerobic conditions. , Furthermore, an efficient and highly selective aerobic catalytic cross-coupling between two different anilines was also established (Scheme B). , Hence, we were interested in extending the existing approaches involving catalytic oxidative homocoupling of anilines under mild aerobic conditions. In this study, we report a heterogeneous metal-catalyzed aerobic oxidative homocoupling of anilines, enabling facile access to various functionalized benzidines and diaminobiaryls under mild conditions (Scheme C).…”