Carborane-Fused Heterocyclic Carbenes: Computational Insights into Stability, Aromaticity, and Potential Synthetic Access via a [3 + 2] Cycloaddition Pathway

Due to the exceptional electronic properties and unique reactivity of the icosahedral ortho-carboranes and the heterocyclic carbenes, their fusion via the carborane C–C bond is expected to lead to interesting results. A facile pathway to synthesize N-heterocyclic fused carboranes was also shown, since the [3 + 2] cycloaddition of carborynes and the corresponding 1,3-heterocumulenes was found to be highly exergonic and practically barrierless. These findings can simplify the way for experimental chemists to utilize the unique electronic properties and promising organocatalytic availability of this family of compounds. Finally, we investigated the reactivity of these new compounds in umpolung-based reactions, showing increased stability for the key Breslow intermediate and hindered reactivity towards aldehyde coupling.