Mallory-Type Reactivity of 1,2-Dihydroazaborinines: 6π-Electrocyclization-[1,5]-H Shift Cascade toward BN-Doped Polycyclic Frameworks

1,2-Dihydro-1,2-azaborinines exhibit highly selective substitution-dependent photochemistry, yielding either Dewar or benzvalene isomers. Through targeted substitution, an o-BN-terphenyl framework is constructed, which undergoes 6π-electrocyclization upon irradiation. The resulting BN-polyenes rearomatize spontaneously via a [1,5]-hydrogen shift. Under oxidative conditions, an unprecedented BN incorporated triphenylene results. By rationally tuning substitution and reaction conditions, this pathway is favored over Dewar isomer formation, offering selective routes to BN-doped polycyclic frameworks from multiphotoresponsive precursors.