Photocatalytic [3 + 2]-annulation <i>via</i> sodium tetraarylborate: a fundamental approach for synthesizing 1,4,2-diazaborole analogs

Substantial advancements have been achieved in the field of photocatalytic borylation utilizing 4c-7e Lewis base-boryl radicals. However, the utilization of 3c-5e neutral boryl radicals for C-B bond formation remains relatively underexplored due to their inherent instability. In this study, we successfully demonstrated the direct construction of C-B bonds using sodium tetraarylborate as a key reagent. This was accomplished by effectively stabilizing diaryl boryl radicals with nitrile compounds, thereby facilitating the synthesis of valuable boron-containing compounds. Overall, our research elucidates the significant role played by sodium tetraarylborate in enabling an efficient and versatile approach for synthesizing of 1,4,2-diazaborole analogs through a photocatalyzed [3 + 2]-annulation reaction. This mild and adaptable methodology expands synthetic strategies for obtaining diverse derivatives of 1,4,2-diazaboroles, with the RCN-BAr₂ complex serving as an effective boron-nitrogen synthon that opens up pathways to multiple boron-nitrogen heterocycles. Furthermore, this breakthrough significantly enhances the applicability of sodium tetraarylborate in photoredox catalysis.