Antiaromatic Sapphyrin Isomer: Transformation into Contracted Porphyrinoids with Variable Aromaticity
Qizhao Li, Masatoshi Ishida, Yunyun Wang, Chengjie Li, Glib Baryshnikov, Bin Zhu, Feng Sha, Xin‐Yan Wu, Hans Ågren, Hiroyuki Furuta, Yongshu Xie
Abstract
Abstract Sapphyrin is a pentapyrrolic expanded porphyrin with a 22π aromatic character. Herein, we report the synthesis of a 20π antiaromatic sapphyrin isomer 1 by oxidative cyclization of a pentapyrrane precursor P 5 with a terminal β‐linked pyrrole. The resulting isomer 1 , containing a mis‐linked bipyrrole unit in the skeleton, exhibits a reactivity for further oxidation due to the distinct antiaromatic electronic structure, affording a fused macrocycle 2 , possessing a spiro‐carbon‐containing [5.6.5.6]‐tetracyclic structure. Subsequent treatment with an acid afforded a weakly aromatic pyrrolone‐appended N‐confused corrole 3 , and thermal fusion gave a [5.6.5.7]‐tetracyclic‐ring‐embedded 14π aromatic triphyrin(2.1.1) analog 4 . The cyclization at the mis‐linked pyrrole moiety of P 5 played a crucial role in synthesizing the antiaromatic porphyrinoid susceptible to facile transformation to novel porphyrinoids with variable aromaticity.