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.