Facile Synthesis of Nonalternant π-Conjugated Azaborines via Boron-Deleting Annulation.

Skeletal editing of aza-heteroarenes has become a powerful strategy for late-stage molecular diversification in medicinal and material chemistry. π-Conjugated azaborines have attracted increasing attention due to their exceptional optoelectronic properties and practical applications in organic light-emitting diodes (OLEDs). However, ring manipulation of boron-containing rings remains a long-standing challenge, and cascade skeletal editing beyond monocyclic frameworks is largely underdeveloped. Here, we report a boron-deleting annulation (BDA) reaction that enables the transformation of unstrained bicyclic 1,4-azaborines into a diaza-pentagon-heptagon pair in a one-pot reaction, affording a wide array of nonalternant π-conjugated azaborines (>35 examples) with unique optoelectronic properties. This late-stage modification approach thus balances synthetic simplicity with structural diversity and expands the accessible chemical space of functional π-systems for optoelectronic applications. Additionally, the BDA product can trigger consecutive cyclodehydrogenation to zipping-up sophisticated nanographenes via further periphery-to-core extension. Mechanistic studies reveal a series of unprecedented ring contraction-expansion processes. Remarkably, yellow OLEDs based on BDA product achieved a record 23.0% external quantum efficiency without delayed fluorescence, demonstrating the potential for high-performance electroluminescence.