Effective N‐Heterocyclic Carbenes with Indole Moiety Applied in the Pd‐Catalyzed Synthesis of Sterically Hindered Biaryls

Abstract

AbstractIndolyl‐based benzimidazolium salts have been designed and prepared using three easy steps, namely indole alkylation, iodine‐catalyzed C−N bond coupling, and substitution. These salts have high catalytic performance in Pd‐catalyzed sterically hindered biaryl synthesis. The variability of the salt scaffold can be modified by the substitution of indole and alkyl halides. The Suzuki‐Miyaura cross‐coupling (SMC) of aryl chlorides was performed with satisfactory functional group tolerance and biaryls were obtained in 42–87% yield at 90 °C by using 0.5 mol% of Pd(OAc)2/1 i as the catalyst. Our results highlight the importance of maintaining a balance between the length of the carbon chain of substituents on the indole moiety and the steric congestion of substituents on the indole moiety for catalytic activity; this can be beneficial in difficult coupling processes. In addition, an asymmetric SMC reaction of aryl chloride under optimal reaction conditions was achieved with an 8% ee preliminarily.