Enantioselective Alkenylation of o-Carboranes via Ir-Catalyzed Asymmetric B-H Activation

The intrinsic chirality of three-dimensional carborane derivatives is established by the substitution patterns on the icosahedral cage, which is much less studied than the planar, axial, central, and helical chirality observed in organic synthesis. Based on transition-metal-catalyzed asymmetrical B-H activation methodology, the addition of functional groups can change the symmetrical o-carborane to chiral-at-cage structures. Herein, we report an asymmetric boron vertex alkenylation of 3-acylamino-o-carboranes with diarylacetylenes for developing the cage (S)-B(4)/(R)-B(7) enantioselectivity of o-carborane. A high efficiency with up to 99% ee can be achieved in the Ir-catalyst-promoted asymmetrical (S)-B(4)-H activation under mild reaction conditions. The enantiocontrol model is suggested on the basis of DFT results where the chiral phosphine ligand plays a crucial role in this catalytic enantioselective B-H activation of o-carborane.