Aromaticity Competition in Differentially Fused Borepin-Containing Polycyclic Aromatics

This report describes the synthesis and characterization of a series of borepin-based polycyclic aromatics bearing two different arene fusions. The borepin synthesis features streamlined Ti-mediated alkyne reduction, leading to Z-olefins, followed by direct lithiation and borepin formation. These molecules allow for an assessment of aromatic competition between the fused rings and the central borepin core. Crystallographic, magnetic, and computational studies yielded insights about the aromaticity of novel, differentially fused [b,f]­borepins and allowed for comparison to literature compounds. Multiple borepin motifs were also incorporated into polycyclic aromatics with five or six rings in the main backbone, and their properties were also evaluated.