Selective B(9)-H Bond Oxidation of o/m-Carboranes with mCPBA

Herein, we have developed an efficient and mild synthetic protocol for the preparation of B(9)-OH-o/m-carboranes by the directly oxidation of o/m-carboranes with mCPBA in hexafluoroisopropanol (HFIP), using trifluoromethanesulfonic acid (HOTf) as a promoter. In comparison to our previously reported method using HNO₃ as the oxidant, the present method demonstrates enhanced mildness, enabling the direct hydroxylation of 1,2-diaryl-o-carboranes and, for the first time, the synthesis of B(8)-hydroxylated o-carborane derivatives. The esterification of 9-OH-o-carborane was further investigated, enabling the successful incorporation of the carboranyl moiety into drug molecules. It provides a material basis for the research of carborane derivatives in coordination chemistry, materials chemistry, and medicine, especially in the field of boron neutron capture therapy (BNCT).