Ir-catalyzed enantioselective B−H alkenylation for asymmetric synthesis of chiral-at-cage o‑carboranes

Abstract

The asymmetric synthesis of chiral-at-cage o-carboranes, whose chirality is associated with the substitution patterns on the polyhedron, is of great interest as the icosahedral carboranes have wide applications in medicinal and materials chemistry. Herein we report an intermolecular Ir-catalyzed enantioselective B−H alkenylation for efficient and facile synthesis of chiral-at-cage o-carboranes with new skeletons under mild reaction conditions. Generally very good to excellent yields with up to 99% ee can be achieved in this Ir-catalyzed B−H alkenylation. The enantiocontrol model is proposed based on Density Functional Theory calculations in which the use of chiral phosphoramidite ligand is essential for such asymmetric o-carborane B−H alkenylation.

Chiral-at-cage o-carboranes are clusters of carbon and boron atoms that, when functionalized, can lower the symmetry of the cluster. Here the authors present a method to alkenylate B–H bonds on ocarboranes enantioselectively via iridium catalysis.