Synthesis and Structure of meso‐Substituted Dibenzihomoporphyrins

Abstract

Bench‐stable meso‐substituted di(p/m‐benzi)homoporphyrins were synthesized through acid‐catalyzed condensation of dipyrrole derivatives with aryl aldehydes. The insertion of a 1,1,2,2‐tetraphenylethene (TPE) or but‐2‐ene‐2,3‐diyldibenzene unit in the porphyrin framework results in the formation of dibenzihomoporphyrins, merging the features of hydrocarbons and porphyrins. Single crystal X‐ray analyses established the non‐planar structure of these molecules, with the phenylene rings out of the mean plane, as defined by the dipyrromethene moiety and the two meso‐carbon atoms. Spectroscopic and structural investigations show that the macrocycles exhibit characteristics of both TPE or but‐2‐ene‐2,3‐diyldibenzene and dipyrromethene units indicating the non‐aromatic characteristics of the compounds synthesized. Additionally, the dibenzihomoporphyrins were found to generate singlet oxygen, potentially allowing their use as photosensitizers.

Synthesis of N-fused dithia and dibenzi homoporphyrins

“…The synthesis of N-fused homoporphyrins is outlined in Scheme 1. The required precursors, dithienyl diol 21 8 , p -phenylene ethene diol 24,25 9a / 9b and N-confused dipyrromethane 27,28 10a / 10b were synthesized over a sequence of reaction steps by following the reported procedures. The diol 8 was synthesized starting from commercially available 2-acetylthiophene in two steps.…”

“…All the required precursors 8 , 9a / 9b and 10a / 10b were characterized by HR-MS and NMR spectroscopy and the characterization data matched with those of the reported compounds. 21,24–27…”

“…17–19 However, due to the synthetic advancements over the years, it is now possible to synthesize the stable azahomoporphyrin 20 III and its core-modified analogues 21,22 IV . Recently, Srinivasan et al , 23 Senge et al , 24 and our group 25 reported the synthesis of dibenzi homoporphyrins ( V ) by condensing m -/ p -phenylene based tetrapyrrane with an aryl aldehyde under acid catalysed conditions. The core-modified homoporphyrins 21,22 IV and the dibenzi homoporphyrins 23–25 V were non-aromatic although azahomoporphyrin 20 III was demonstrated to be Mobius aromatic in nature.…”

“…Recently, Srinivasan et al , 23 Senge et al , 24 and our group 25 reported the synthesis of dibenzi homoporphyrins ( V ) by condensing m -/ p -phenylene based tetrapyrrane with an aryl aldehyde under acid catalysed conditions. The core-modified homoporphyrins 21,22 IV and the dibenzi homoporphyrins 23–25 V were non-aromatic although azahomoporphyrin 20 III was demonstrated to be Mobius aromatic in nature. Gao and co-workers recently reported the thiophene-embedded N-confused homoporphyrin VI consisting of a 5,5,5-tricyclic fused ring, which is non-aromatic in nature.…”

Phenanthrene cyclocarbonylation – core post-synthetic modification of phenanthriporphyrin

“…Formally 5 can be derived from phenanthriporphyrin 1 merely by hydrogenolysis of the C(22)–C(25) bond. 11 Fluorenophyrin 6 , and its keto derivative 6-CO were synthesized by Ravikanth et al starting from fluorene as a fundamental building block. 12,13…”