Electrophilic aromatic reactivity. Part 24. Protiodetritiation of pentahelicene (dibenzo[c,g]phenanthrene)

Visualizing electron delocalization in contorted polycyclic aromatic hydrocarbons

“…The delocalization patterns visualized in Fig. 2 for [n]helicenes match with the experimentally determined rate factor of all positions of [n]helicenes in some electrophilic aromatic substitution reactions, [64][65][66] with the H-substituted carbon atoms showing the less delocalization over them in the maps being among the most reactive positions. Please do not adjust margins…”

Helicenes: Synthesis and Applications

“…Castle and co-workers synthesized thiahetero[5]helicene 167 by a photocyclization method. Unlike in the preparation of carbo[5]helicene, where the yield of the linear product 27 was negligible, reaction of 166 gave two isomers 167 and 168 in 50% and 37% yields, respectively (Scheme ) . This low regioselectivity might result from the smaller energy gap of the reaction (8.6 kcal/mol; the energy gap for photocyclization of the corresponding carbohelicene is 17.4 kcal/mol) .…”