Synthesis and Structural Analysis of Porphyrin‐Based Polynucleating Ligands Bearing 8‐Methoxy‐ and 8‐(Allyloxy)quinoline Units

Abstract

AbstractThe synthetic strategies and procedures leading to a series of new porphyrin derivatives bearing two to four 8‐hydroxyquinolinyl groups are reported. The solid‐state structures of the majority of the reported porphyrin derivatives were investigated by X‐ray diffraction analysis of single crystals. The strategy, based on the condensation of the carboxylic acid derivative of methyl‐protected 8‐hydroxyquinoline with the pure α4, α2β2 and αβαβ atropoisomers of tetrakis(o‐aminophenyl)porphyrin precursors in the presence of HBTU/DMAP led to the formation of the corresponding tetrasubstituted derivatives in good yields (45–68 %). Unfortunately, the final deprotection step leading to the desired chelating compounds was unsuccessful. The replacement of the methyl group by the bulky allyl group afforded only the di‐ and trisubstituted α4 atropoisomer in 17 and 50 % yields, respectively. Due to steric reasons, no trace of the tetrasubstituted α4 atropoisomer derivative was detected. However, the coupling reaction with the αβαβ atropoisomers of the tetrakis(o‐aminophenyl)porphyrin precursor afforded the tetrasubstituted atropoisomer in 49 % yield. Again, the deprotection step was problematic and led to non‐separable mixtures. Finally, the desired α4 atropoisomer bearing four 8‐hydroxyquinolinyl groups was obtained upon direct condensation of the α4 atropoisomer of the precursor with 8‐hydroxy‐7‐quinolinecarboxylic acid in the presence of activating agents (HBTU and DMAP).