Pd-Catalyzed Vicinal Difunctionalization of Carboranes with Benzoxazoles, Indoles and Anilines

Abstract

Icosahedral Carboranes have a wide range of applications in medicinal chemistry, material science, and catalysis. Although various methods have been disclosed for functionalizing carborane structures, the methods to incorporate different types of heterocycles are still lacking. This limitation is likely due to the functional group incompatibility under previously reported reaction conditions, and the sterically hindered environment on boron cluster vertices further complicated the reaction development. In this article, we present a streamlined protocol to prepare a new class of vicinal difunctionalized carboranes containing benzoxazoles, NH heterocycles and anilines. This method involves a direct cross-coupling between 9-bromo-m-carborane and benzoxazoles, thereby eliminating the necessity for preceding deprotonation of the acidic C2 proton present in benzoxazole. Subsequent regioselective iodination at the B(10) vertex of the carborane and the second cross-coupling reactions with diverse indoles and anilines resulted in the formation of the desired vicinal difunctionalized products.