Skeletal Editing of Aromatic N-Heterocycles via Hydroborative Cleavage of C−N Bonds—Scope, Mechanism, and Property

Skeletal editing of the core structure of heterocycles offers new opportunities for chemical construction and is a promising yet challenging research topic that has recently gained increasing interest. However, several limitations of the reported systems remain to be addressed. For example, the reagents employed are generally in high-energy, such as chlorocarbene precursors, nitrene species, and metal carbenes, which are also associated with low atomic efficiencies. Thus, the development of simple systems for the skeletal editing of heterocycles is still desired. Herein, a straightforward and facile BH₃-mediated skeletal editing of readily available indoles, benzimidazoles, and several other aromatic heterocycles is reported. Structurally diverse products were readily obtained, including tetrahydrobenzo azaborinines, diazaboroles, O-anilinophenylethyl alcohols, benzene-1,2-diamines, and more. Density functional theory (DFT) calculations and natural bond orbital (NBO) analysis revealed a BH₃-induced C−N bond cleavage reaction pathway. An exciting and counterintuitive indole hydroboration phenomenon of −BH₂ shift from C3-position to C2-position was disclosed. Moreover, the photophysical properties of the synthesized diazaboroles were studied, and an interestingly and pronounced aggregation-induced emission (AIE) behavior was disclosed.