An efficient synthesis of conjugation-expanded carba- and azuliporphyrins using a bicyclo[2.2.2]octadiene-fused tripyrrane

A bicyclo[2.2.2]octadiene-fused tripyrrane was synthesized as a first versatile reagent for the preparation of π-expanded heteroporphyrins. The reaction of the tripyrrane with 1,3-diformylindene and azulene-1,3-dicarbaldehyde afforded the corresponding heteroporphyrins, which were easily converted into tetrabenzocarbaporphyrin and tribenzoazuliporphyrin by retro Diels–Alder reaction.