Distance-Triggered Distinct Aryl Migrations on Azidodiboranes

Derived from structurally similar precursors, two different azidodiboranes went through distinct aryl migration reactions triggered by different boron-boron separation distances. Biphenylene based diborane with a shorter boron-boron distance underwent heterolateral aryl migration to form a seven-membered azadiborepin, while xanthrene based diborane with a longer boron-boron distance afforded a stable bis-azidoborane scaffold. The pyrolysis of such a bis-azidoborane led to eight-membered oxazadiborocine through homolateral aryl migration and subsequent [3+2] cycloaddition. Density functional theory (DFT) calculations unveiled that the boron-boron separation distances were the intrinsic factors for the distinct migrations.