Synthetic access to organyl-substituted 1,2,3-benzodiazaborines with turn-on fluorescence activity

1,2,3-Benzodiazaborines (DABs), isoelectronic to isoquinoline alkaloids, have attracted considerable interest due to their unique reactivity and promising potential applications, including but not limited to pH sensors, chiral probes or antibacterial agents. Although DABs with hemiboronic acid functionality have been known since the 1960s and were extensively studied since then, a method to convert the borinic acid functionality into a borane moiety with carbon-based substituents has remained elusive and is of interdisciplinary interest. Herein, we present a straightforward and inexpensive two-step synthesis of aryl- and alkyl-substituted DABs starting from established hemiboronic acid derivatives and commercially available reagents. Computational studies on the electronic situation of the aryl-substituted derivatives revealed a more pronounced degree of aromaticity compared to the parent hemiboronic acid compounds. The synthesized DABs proved to be highly sensitive multi-anion fluorescence "turn-on" chemosensors for detection and differentiation of relevant anions such as cyanide (CN^-) and fluoride (F^-). Overall, the synthetic approach presented herein expands the library of accessible DABs to alkyl and aryl derivatives and opens new possibilities to functionalize these BN-alkaloids for applications in fields like fluorescence sensing, material science, and medicinal chemistry.