New Angular Polycyclic Aromatic Boron Heterocycle Ring Systems

2‐Formylphenylboronic acid condenses with salicyloyl and anthraniloyl hydrazines directly to generate dibenzo‐fused versions of [1,2,3]diazaborinino[3,2‐b][1,3,2]oxazaborinine and [1,3,2]diazaborinino[1,2‐b][1,2,3]diazaborinine, respectively, in excellent yields. These compounds, the first members of heretofore unknown planar polycyclic boron heterocycle ring systems, were characterized thoroughly by high‐field NMR spectroscopy, X‐ray crystallography, and other techniques.