Document Type

Article

Publication Date

2026

Publication Title

Tetrahedron

Keywords

porphyrin synthesis, heteroporphyrins, carbaporphyrins, aromaticity, tripyrranes

Abstract

Tripyrranes with terminal ester protective groups were prepared by reacting 7-acetoxy-4,5,6,7-tetrahydroindoles with 3,4-diethylpyrrole in refluxing acetic acid-ethanol. Dibenzyl esters were deprotected by hydrogenolysis over 10% Pd/C and the resulting dicarboxylic acids were condensed with a series of dialdehydes in the presence of trifluoroacetic acid, followed by oxidation with FeCl3 or DDQ, to give porphyrinoid products with two six-membered exocyclic rings. Reactions with a pyrrole dialdehyde gave porphyrins in 27-30% yield and good yields were also obtained using 2,5-furandicarbaldehyde and 4-hydroxy-2,6-pyridinedicarbaldehyde to prepare oxaporphyrins and oxypyriporphyrins. However, poorer results were noted for thiaporphyrins, benzocarbaporphyrins and oxybenziporphyrins due to their poor stability in solution. The UV-vis spectra for these porphyrinoids showed significant bathochromic shifts compared to structures without 6-membered carbocyclic rings and in every case the proton NMR spectra showed that the diatropic ring currents associated with the macrocycles were reduced. These data give valuable insights into the properties of modified porphyrinoid systems and provide the foundations for investigations into the preparation of new porphyrinoid architectures.

Funding Source

This work was supported by the National Science Foundation under CHE-2247214. NSF is also acknowledged for providing funding for the departmental NMR spectrometers (CHE-0722385), and high-resolution mass spectrometer (CHE-1337497) under the Major Research Instrumentation (MRI) program. This article was published Open Access thanks to a transformative agreement between Milner Library and Elsevier.

DOI

10.1016/j.tet.2026.135235

Comments

First published in Tetrahedron (2026): https://doi.org/10.1016/j.tet.2026.135235. Supplementary data available on the publisher's site.

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