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The reactions of the dioxonium derivative of closo dodecaborate(12) with aromatic alde hydes and esters containing O and N nucleophilic centers were studied. These reactions were used to synthesize new closo dodecaborate based building blocks containing aldehyde and acid ic groups.Among a broad range of boron compounds, functional derivatives of the closo dodecaborate dianion [B 12 H 12 ] 2-are the most interesting as promising agents for boron neu tron capture therapy (BNCT) of cancer. 1 This is associat ed with their low toxicity, as well as with high solubility of their alkali metal salts in water. The sodium salt of mer capto closo dodecaborate Na 2 [B 12 H 11 SH] is one of two drugs for BNCT used in clinical practice. 2 The main prob lem in the chemistry of [B 12 H 12 ] 2-is that the cluster con tains 12 equivalent boron vertices, which strongly hinders the introduction of a reaction center. The synthesis of cy clic oxonium derivatives of [B 12 H 12 ] 2-(1) and their cleav age by nucleophiles was a breakthrough in the chemistry of this dianion. 3-5 This approach was used to synthesize de rivatives of the B 12 cluster with various active molecules, such as natural porphyrins, 6 phthalocyanines, 7 cholester ols, 8 coumarins, 9 etc. Oxonium derivatives can also be used in the synthesis of building blocks, i.e., derivatives con Scheme 1

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