Ring-Closing and Ring-Opening of closo-B12-Fused Carboxonium Ions: PIDA-Mediated Synthesis and Reactivity toward Neutral O‑Nucleophiles

This paper reports on a synthetic approach to 1,2-disubstituted carboxonium derivatives [1,2-B12H10O2CR]− that combines acylation and (diacetoxyiodo)benzene-promoted cyclization reactions. The formation pathway of the carboxonium ring fused to the closo-dodecaborate was examined using DFT calculation and it was found that the reaction includes two main transition states corresponding to the deprotonation-iodination of the cluster and intramolecular cyclization. It was established that the nature of the R-substituent significantly affects the stability of the carboxonium ring to opening processes initiated by water and alcohols. It was also demonstrated that, depending on the nucleophilicity of the reagent, both mixed derivatives with hydroxy and acyloxy groups and dihydroxy derivatives can be obtained.