An original transition metal-free approach based on the direct CC coupling of phtalazine-N-oxide with the carboranyl anion has been developed. A series of the novel C-modified closo-carboranes such as 1-(2-oxido-3-acyl-3,4-dihydrophtalazinyl-4-yl)-1,2-dicarba-closo-dodecaboranes and 1-(2-formylbenzyl)-1,2-dicarba-closo-dodecaborane have been obtained. The synthesized boron clusters could be of interest as promising building blocks in design of BNCT delivery agents.