A new motif for artificial double helices was developed on the basis of α,α′-disubstituted tripyrrin.

Double ring expansion from a 5,15-diarylporphyrin to a 5,16-diaryl-10,11,21,22-tetradehydro[20]porphyrin(2.1.2.1) occurred through a reaction sequence consisting of oxidation with PbO2 to 5,15-dioxoporphodimethene, a Corey-Fuchs reaction with tetrabromomethane in the presence of triphenylphosphine, and Fritsch-Buttenberg-Wiechell rearrangement triggered by tert-butyllithium. The obtained tetradehydro[20]porphyrin(2.1.2.1) and its mono- and dihydrogenated congeners exhibited 20 π antiaromatic character, whereas overhydrogenated congeners bearing a saturated bridge were nonaromatic owing to disrupted π conjugation.

Di-peri-dinaphthoporphyrins can be regarded as a key and common substructure of fused porphyrinoids. PtCl2 -mediated cycloisomerization reaction of quinodimethane-type porphyrins provided these doubly fused porphyrins, which exhibit characteristic paratropic ring currents that presumably arise from 24π antiaromatic circuit as a dominant resonance contributor. UV/Vis absorption spectra, cyclic voltammetry, and excited-state dynamics as well as theoretical calculation support this conclusion.

5,20-Diheterohexaphyrins with variable aromatic characters have been synthesized for the first time.