Controlled Core‐Modification of a Porphyrin into an Antiaromatic Isophlorin

Abstract

Partial core‐modification of a porphyrin can be employed to synthesize the 20π antiaromatic isophlorin. Unlike the tetra‐, tri‐, and dipyrrole derivatives of a porphyrin, a monopyrrole porphyrin exhibits antiaromatic characteristics. It undergoes a two‐electron reversible ring oxidation to yield the 18π aromatic dication. 1H NMR analysis provides distinct evidence of the altered electronic characteristics through typical paratropic and diatropic ring current effects for the 4n and the (4n+2) π‐electron systems, respectively.