Bifunctional Silylene-Aminoborane Enables Cooperative Activation of Unsaturated Bonds and Access to Heteroatom-Enriched Polycycle.

We report the synthesis and cooperative reactivity of a bifunctional silylene-aminoborane compound, 1-Ph-2-^tBu-1H-2,1-benzazaborolyl-(amidinato)silylene (1), designed to preserve the ambiphilicity of both functional units while preventing intramolecular deactivation. 1 engages in unprecedented multicomponent activations of unsaturated bonds, including alkynes and phosphaalkynes, to construct novel main-group element embedded polycyclic frameworks. Reaction with alkynes led to rare main-group elements enriched semibullvalenes via highly regioselective [2 + 2 + 1] cycloaddition. Notably, reaction with a phosphaalkyne induced a distinct S_NAr-like B─C bond cleavage and formation of a B─N─Si─P-embedded barrelene analogue. Structural and computational analyses revealed the synergistic multi-site activation modes and reaction pathways.