Carborane-Based Lewis Base Catalysts for Aromatic Halogenation

Haloarenes have been an important class of chemicals in modern organic chemistry field because the halide functionality offers numerous possible transformations. Classical electrophilic aromatic halogenation using molecular halogens and Lewis/Brønsted acid activators is still a promising synthetic tool; however, it suffers from handling difficulties, low selectivity, and limited functional group tolerance. We herein introduce carborane-based Lewis base catalysts for the aromatic halogenation using N-halosuccinimides. The developed reaction system was readily applicable to late-stage functionalization of drug molecules and efficient synthesis of multi-halogenated aromatics. The m-carborane scaffold was most suitable for the catalysis, and the possible fine-tuning by decorating the cluster vertices was important for modulating the electronic property of halonium species to maximize the catalytic performance.