Synthesis of Benziporphyrins and Heterobenziporphyrins and an Assessment of the Diatropic Characteristics of the Protonated Species

Benzitripyrranes
were prepared by reacting diphenyl-substituted
benzenedicarbinols with excess pyrrole in the presence of BF3·Et2O. These dipyrrolic compounds underwent acid-catalyzed
condensations with a pyrrole dialdehyde to afford good yields of diphenylbenziporphyrins,
and further reaction with palladium­(II) acetate gave stable organometallic
derivatives. The X-ray crystal structure of a palladium­(II) benziporphyrin
showed that the system deviates significantly from planarity. Although
the benzitripyrranes failed to give stable macrocyclic products with
furan or thiophene dialdehydes, they afforded tetraphenyl heterobenziporphyrins
upon reaction with diphenyl-substituted furan- or thiophenedicarbinols
and BF3·Et2O. Benziporphyrins and their
heteroanalogues showed no indication of a diamagnetic ring current
by proton NMR spectroscopy, but addition of TFA gave rise to the formation
of weakly diatropic dications.