Biomimetic Synthesis of an Octavinylogous Porphyrin with an Aromatic [34]Annulene System

Abstract

The validity of the Hückel rule extends considerably further than hitherto assumed the limit is in no way already reached with the diatropic, aromatic [22]annulene. The deep-blue title compound was isolated as the octaethyl-N,N′,N″,N‴-tetramethyl dibromide. Its diamagnetic ring-current effect is unusually large; the shift difference between inner and outer protons is 31.5 ppm!