Site- and enantioselective B-H functionalization of carboranes

Functionalization of carboranes, icosahedral boron-carbon molecular clusters, is of great interest as they have wide applications in medicinal and materials chemistry. Thus, site- and enantioselective synthesis of carboranes requires complete control of the reaction. Herein, we describe the asymmetric Rh(II)-catalyzed insertion reactions of carbenes into cage B-H bond of carboranes. This reaction thereby generates carboranes possessing a carbon-stereocenter adjacent to cage boron of the carborane, in excellent site- and enantioselectivity under mild reaction conditions. The fully computed transition structures of Rh(II)-catalyzed carbene insertion process through density functional theory are reported. These B-H insertion transition structures, in conjunction with topographical proximity surfaces analyses, visually reveal the region between the carborane and the phthalimide ligands responsible for the selectivities of this reaction.