Palladium-Catalyzed Regioselective B(3,4,5,6)–H Tetra-Arylation of o-Carboranes

A transition-metal-catalyzed iterative multiple cage B–H activation reaction for constructing multifunctionalization of o-carboranes in one pot is challenging. Herein, palladium-catalyzed regioselective tetra-arylation of a wide range of C(1)-N-aryl-o-carboranyl amides with aryl iodides has been developed. A variety of B(3,4,5,6)-tetra-arylated o-carboranes were synthesized in good-to-excellent yields. Moreover, the mono-, di-, and triarylated intermediate products were isolated, and the exact structures were determined by NMR, high-resolution mass spectrometry, and X-ray analysis, which provide a rationale that the order of introduction of aryl groups into o-carborane is B(4) > B(5) > B(3)/B(6). This protocol represents a powerful synthetic method for constructing polyfunctionalization of o-carborane derivatives under very mild and simple reaction conditions, which offers a valuable reference for the design and synthesis of molecular propellers based on carboranes.