Computational, Mechanistic, and Experimental Insights into Regioselective Catalytic C–C Bond Activation in Linear 1‑Aza-[3]triphenylene

C–C bond activation
by transition metal complexes in ring-strained
compounds followed by annulation with unsaturated compounds is an
efficient approach to generate structurally more complex compounds.
However, the site of catalytic C–C bond activation is difficult
to predict in unsymmetrically substituted polycyclic systems. Here,
we report a study on the (regio)­selective catalytic cleavage of selected
C–C bonds in 1-aza-[3]­triphenylene, followed by annulation
with alkynes, forming products with extended π-conjugated frameworks.
Based on density functional theory (DFT) calculations, we established
the stability of possible transition metal intermediates formed by
oxidative addition to the C–C bond and thus identified the
likely site of C–C bond activation. The computationally predicted
selectivity was confirmed by the following experimental tests for
the corresponding Ir-catalyzed C–C cleavage reaction followed
by an alkyne insertion that yielded mixtures of two mono-insertion
products isolated with yields of 34–36%, due to the close reactivity
of two bonds during the first C–C bond activation. Similar
results were obtained for twofold Ir- or Rh-catalyzed insertion reactions,
with higher yields of 72–77%. In a broader context, by combining
DFT calculations, which provided insights into the relative reactivity
of individual C–C bonds, with experimental results, our approach
allows us to synthesize previously unknown pentacyclic azaaromatic
compounds.