Insights into the regioselectivity of the N-directed electrophilic borylation of N,N-dipyridyl-N,N-dihydrophenazine.

N-directed borylation of polycyclic aromatic hydrocarbons (PAHs) is emerging as a versatile approach to the synthesis of novel photoactive materials for optoelectronic, imaging, sensing, and photocatalysis applications. We show here that while the N-directed bis-borylation of N,N-dipyridyl-N,N-dihydrophenazine (Pz) predominantly produces a B-N-fused cis-isomer with both boryl groups attached to the same benzene ring, the trans-isomer is also generated as a minor component. We report the isolation and detailed characterization of cis-BNPz and trans-BNPz, as well as a mono-functionalized intermediate, mono-BNPz. The optical and electronic properties of the regioisomers are compared. In addition, computational studies shed light on the reaction pathways involved, offering insights into the origin of regioselectivity and revealing a process that proceeds without an external base.