New porphyrinoids, 9. Synthesis of a bisvinylogous porphyrin with a [22] annulene system

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Abstract
The twofold vinylogously enlarged porphyrin with a 22‐π‐electron system 3 was prepared by vinylogous bisformylation of the dipyrrylmethane 7 to give 8 and subsequent acid‐catalyzed condensation of 8 with 7. The [22]porphyrin 3 is characterized by a Soret band at 469 nm, which on protonation of the porphyrinoid becomes very narrow with the highest extinction coefficient so far observed for an organic pigment (ϵ = 1090000). In the 1H‐NMR spectrum 3 reveals a strong diamagnetic ring‐current effect with a shift difference between inner and outer protons of Δδ = 20.1 ppm, thereby proving itself a pronounced aromatic system.