Octaethyl-1,3-oxazinochlorin: A β‑Octaethylchlorin Analogue Made by Pyrrole Expansion

Treatment of the oxime of octaethyloxochlorin <b>4</b>, available from octaethylporphyrin <b>3</b>, under Beckmann conditions provided not the expected lactam, but octaethyl-1,3-oxazinochlorin <b>8</b>, in which a pyrrole moiety of the parent oxochlorin was expanded by an oxygen atom to an 1,3-oxazinone moiety. Its mechanism of formation was demonstrated to occur along an “abnormal Beckmann” pathway, followed by intramolecular ring closure and hydrolysis. The work expands the methodologies known to convert octaethylporphyrin to pyrrole-modified porphyrin analogues

Synthesis, Structural Characterization, Aromatic Characteristics, and Metalation of Neo-Confused Porphyrins, a Newly Discovered Class of Porphyrin Isomers

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 <i>meso</i>-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

Synthesis, Structural Characterization, Aromatic Characteristics, and Metalation of Neo-Confused Porphyrins, a Newly Discovered Class of Porphyrin Isomers

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 <i>meso</i>-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