The synthesis of corticosteroid–carborane esters for the treatment of rheumatoid arthritis via boron neutron capture synovectomy

Facile and Efficient Synthesis of C-Hydroxycarboranes and C,C‘-Dihydroxycarboranes

C-Hydroxylated carboranes, carboranols, have interesting properties resulting from their hydroxyl protons being highly acidic because of the electron-deficient nature of the carborane cage. We described here an efficient synthesis of C-hydroxycarboranes 2 and C,C'-dihydroxycarboranes 3 by the reaction of carboranyl lithium and trimethylborate, followed by oxidation with hydrogen peroxide in the presence of acetic acid, to afford the corresponding o-, m-, and p-hydroxycarboranes 2 and o-, m-, and p-dihydroxycarboranes 3 selectively in high yields through a one-pot procedure. The m- and p-carborane isomers of 2 and 3 were obtained in especially good yields (2b, 85%; 2c, 85%; 3b, 95%; 3c, 96%). DFT calculations were performed on the dihydroxycarboranes 3 to compare the geometrical features of the isomers at the same level of theory and to characterize their electronic and NMR spectroscopic (13C chemical shift) properties.