Aromatic 1,4,2,3‐Diazadiborole Featuring an Unsymmetrical B=B Entity: A Versatile Synthon for Unusual Boron Heterocycles.

The replacement of a CC unit with an isoelectronic BN unit in aromatic systems can give rise to molecules and materials with fascinating properties. We report here the synthesis, characterization, and reactivity of a 1,4,2,3‐diazadiborole species, 2, featuring an unprecedented 6π‐aromatic BN‐heterocyclic moiety that is isoelectronic to cyclopentadienide (Cp−). Bearing an unsymmetrical B=B entity, 2 exhibits reactivity toward oxidants, protic reagents, electrophiles, and unsaturated substrates. This reactivity facilitates the synthesis of a variety of novel mono‐ and bicyclic organoboron derivatives through mechanisms including ring retention, cleavage/recombination, annulation, and expansion. These findings reveal innovative synthetic routes to BN‐embedded aromatic compounds via desymmetrization, affording unique building blocks for synthetic chemistry. [ABSTRACT FROM AUTHOR]