- Intermolecularly hydrogen-bonded dimeric helices: tripyrrindiones
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A rare and unusual class of tripyrrolic compounds, violet-colored tripyrrin-1,14-diones, can be prepared easily and in moderately high yields from base (piperidine)-catalyzed condensation of 3-pyrrolin-2-ones with 2,5-diformylpyrroles. Dipyrrinones adopt the all-syn-Z conformation leading to helical, lock-washer like structures, which form dimers that are held together by intermolecular hydrogen bonds in nonpolar solvents and in the crystal. Strong bathochromic spectral shifts of the tripyrrindione ~480 nm long wavelength UV-visible absorption band are seen with added base: DBU, 615 nm; TFA, 573 nm; and Zn(OAc)2, 586 nm.
- Roth, Steven D.,Shkindel, Tetyana,Lightner, David A.
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- Synthesis, structural characterization, aromatic characteristics, and metalation of neo-confused porphyrins, a newly discovered class of porphyrin isomers
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Neo-confused porphyrins represent a unique family of porphyrin isomers that retain overall aromatic characteristics by virtue of a 17-atom 18π electron delocalization pathway. These porphyrin analogues have a pyrrolic subunit linked in a 1,3-fashion so that a nitrogen atom is directly connected to a meso-bridging carbon. Pyrrole-3-carbaldehydes were shown to react with sodium hydride and 5-acetoxymethylpyrrole-2-carbaldehydes in DMF to give the crucial neo-confused dipyrrolic dialdehyde intermediates. MacDonald "2 + 2" condensation of the dialdehydes with a dipyrrylmethane afforded a dihydroporphyrinoid, and subsequent oxidation with 0.2% aqueous ferric chloride generated a series of fully conjugated neo-confused porphyrins. Unusual dihydroporphyrin byproducts were also identified. Reaction of neo-confused porphyrins with nickel(II) or palladium(II) acetate in refluxing acetonitrile gave excellent yields of the corresponding organometallic derivatives. Proton NMR spectroscopy demonstrates that the diatropic character of this system is diminished compared to regular porphyrins, although neo-confused porphyrins retain porphyrin-like UV-vis spectra. Protonation led to the sequential formation of mono- and dicationic species. Proton NMR spectra for the dications showed the presence of enhanced diamagnetic ring currents.
- Li, Ruoshi,Lammer, Aaron D.,Ferrence, Gregory M.,Lash, Timothy D.
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- New one-step synthesis of 3,4-disubstituted pyrrole-2,5-dicarbaldehydes
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A smooth and convenient one-step synthesis of 3,4-disubstituted pyrrole- 2,5-dicarbaldehydes 2 is reported. This reaction involves the condensation of β-substituted pyrrole-2-carboxylic acids with triethyl orthoformate in trifluoroacetic acid to give the title compounds in good yield.
- Tardieux, Catherine,Bolze, Frederic,Gros, Claude P.,Guilard, Roger
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- Acetylene-cumulene porphycene compounds for photodynamic therapy
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Dihydro- and tetrahydro-acetylene-cumulene porphycene compounds having the structure shown below STR1 are useful as photogynamic therapy agents.
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