Synthesis of 2-Boryl- and Silylindoles by Copper-Catalyzed Borylative and Silylative Cyclization of 2-Alkenylaryl Isocyanides

We have developed a method for the synthesis of 2-borylindoles via the copper(I)-catalyzed borylative cyclization of 2-alkenylphenyl isocyanides using diboronate. The reaction proceeds at room temperature under neutral conditions and exhibits high tolerance to functional groups, such as Br, CO2R, COR, CONMe2, and CN. The 2-borylindoles synthesized in the present study can be elaborated into an array of indole-based derivatives, for example, through the Suzuki−Miyaura reaction. The utility of this method is demonstrated in the rapid synthesis of a kinase inhibitor, paullone. The reaction can be extended to the synthesis of 2-hydride indole and 2-silylindole by using hydroboronate (or hydrosilane) and silylboronate, respectively. Under these copper-catalyzed conditions, a quinoxaline ring system can also be constructed by using 1,2-isocyanobenzene as a substrate.