Synthesis of monosubstituted functional derivatives of carboranes from 1-mercapto-ortho-carborane: 1-HOOC(CH2)(n)S-1,2-C2B10H11 and [7-HOOC(CH2)(n)S-7,8-C2B9H11](-) (n=1-4)

A general approach to synthesis of monosubstituted functional derivatives of 1,2-dicarba-closo-dodecaborane (ortho-carborane) is proposed. Reactions of the triethylammonium salt of 1-mercapto-ortho-carborane (Et3NH)[1-S-1,2-C2B10H11] with ethyl omega-bromoalkyl carboxylates and omega-bromoalkylnitriles in ethanol result in the corresponding carboranyl esters and nitriles that in turn can be converted to carborane-based carboxylic acids 1-HOOC(CH2)(n)S-closo-1,2-C2B10H11 (n = 1-4). Mild deboronation of the closo-carborane cage with CsF in ethanol gives caesium salts of the corresponding nido-carboranes Cs[7-HOOC(CH2)(n)S-nido-7,8-C2B9H11]. This approach is suitable for synthesis of compounds to be used in boron neutron capture therapy and radionuclide diagnostics of cancer.