Functionalization of o-carboranes via carboryne intermediates

Abstract

Carborynes (1,2-dehydro-o-carborane and 1,3-dehydro-o-carborane), three-dimensional analogues of benzyne, can be generated in situ from the precursors 1-X-2-Li-1,2-C₂B₁₀H₁₀ (X = Br, I, OTs, OTf), or 1-Me₃Si-2-[IPh(OAc)]-1,2-C₂B₁₀H₁₀ or [1-Li-3-N₂-1,2-C₂B₁₀H₁₀][BF₄]. They are a class of very useful synthons for the synthesis of a large variety of functionalized carborane derivatives for potential application in medicine, materials science and organometallic/coordination chemistry. The experimental data demonstrate that there is a correspondence between the reactions of carborynes and those of benzyne with alkenes, dienes, alkynes, aromatics or heteroaromatics in a pericyclic reaction fashion. On the other hand, carborynes have unique properties of their own owing to their steric/electronic features. They undergo regioselective sp²/sp³ C-H bond and N-Li bond insertion reactions, which has not been observed for benzyne. This review provides a comprehensive overview of recent advances in this interesting research field with considerable attention devoted to the reaction modes and the mechanisms involved.