β-Trioxopyrrocorphins: pyrrocorphins of graded aromaticity

Chaudhri, Nivedita; Guberman‐Pfeffer, Matthew J.; Li, Ruoshi; Zeller, Mat­thias; Brückner, Christian

doi:10.1039/d1sc03403k

Cited by 6 publications

(31 citation statements)

References 66 publications

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“…Thus, chromatographic separation of the reaction mixture isolates all possible isomers of the β,β′-dioxo derivatives (three isomers of the isobacteriochlorin series 6 ; two isomers of the bacteriochlorin series 7 ) and two (out of the four possible) triketone isomers 8 , as well as meso -oxo-substituted phlorins and ring-opened products . We recently presented a more directed synthesis of the remaining constitutional isomers of the triketones …”

Section: Introductionsupporting

confidence: 85%

“…This produced, as expected, the corresponding dioxo-osmate esters, as indicated by the diagnostic signals of osmium-coordinated pyridine moieties in their 1 H NMR spectra (see SI). The oxidation of 6-O 3,7 also resulted in the formation of a small portion of triketone isomer 8-O 2,8,18 (one of the rare isomers among the triketones) . While it is tempting to assume that the product is the product of adventitious cleavage of the osmate ester/rearrangement of the diol, deliberate acid-induced rearrangement of the corresponding diol formed a different trioxopyrrocorphin isomer, namely, 8-O 2,7,18 (see below).…”

Section: Results and Discussionmentioning

confidence: 99%

“…The general electronic influences of the β-oxo substituents have been well described within the realm of mono- and bis-β-oxo-substituted porphyrinoids (including the ketone functionalities of the porpholactones). , d, These studies also revealed regiochemical influences and the effects on the aromaticity parameters of the chromophores We recently presented work on all isomers of the pyrrocorphin β-triketones . We showed that they exhibit an aromatic macrocycle, expressed through a 16-membered, 18 π-macrocycle anion chromophore along a so-called inner–inner–inner–outer conjugation pathway, whereas all constitutional isomers of the triketones exhibit much different degrees of aromaticity .…”

Section: Introductionmentioning

confidence: 99%

“…d, We recently presented work on all isomers of the pyrrocorphin β-triketones . We showed that they exhibit an aromatic macrocycle, expressed through a 16-membered, 18 π-macrocycle anion chromophore along a so-called inner–inner–inner–outer conjugation pathway, whereas all constitutional isomers of the triketones exhibit much different degrees of aromaticity . The chemistry of the mono- and diketones was explored to some extent; , however, the chemistry of the β-triketones 8 was, aside from limited coordination chemistry studies, largely ignored.…”

Section: Introductionmentioning

confidence: 99%

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Stepwise Reduction of β-Trioxopyrrocorphins: Collapse of the Oxo-Induced Macrocycle Aromaticity

et al. 2022

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The diatropic ring current that characterizes the unexpectedly aromatic octaethyltrioxopyrrocorphins gets drastically reduced upon chemical reduction of one and particularly two ketone moieties. With increasing reduction, the chromophores containing one pyrrole, one/two pyrrolinone, and one/two pyrrolines become more similar to regular, nonmacrocycle–aromatic pyrrocorphins (hexahydroporphyrins). Single-crystal diffraction analysis shows the reduction products to be idealized planar. With increasing reduction, their UV–vis spectroscopic signatures are those of conjugated but nonaromatic oligopyrroles. Their diatropic ring currents, as assessed by 1H NMR spectroscopy, showed them to possess largely nonaromatic π-systems. Dihydroxylation of select β,β′-dioxobacteriochlorin and β,β′-dioxoisobacteriochlorins also resulted in the formation of equivalent mixed pyrrole/two pyrrolinone/pyrroline chromophores. Computations were able to reproduce the experimental trends of the diatropic ring currents and filled in the data for the regioisomers that could not be experimentally accessed. The work further highlights the electronic influence of the β-oxo-substituents and, more specifically, the origin of the aromaticity of the trioxopyrrocorphins. It also presents a series of chemically robust pyrrocorphins, a chromophore class for which many chemically very sensitive members have been reported.

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Section: Introductionsupporting

confidence: 85%

Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Stepwise Reduction of β-Trioxopyrrocorphins: Collapse of the Oxo-Induced Macrocycle Aromaticity

et al. 2022

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“…Porpholactones with more than two lactone moieties have not been reported to date, although mixed tris-modified systems, such as compound 8 , have become known . Other tris-substituted systems are the octaethyltriketones prepared by the oxidation of octaethylporphyrin …”

Section: Introductionmentioning

confidence: 99%

Syntheses and Aromaticity Parameters of Hexahydroxypyrrocorphin, Porphotrilactones, and Their Oxidation State Intermediates

et al. 2022

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Triple OsO4-mediated dihydroxylation of meso-tetrakis(pentafluorophenyl)porphyrin formed a non-aromatic hexahydroxypyrrocorphin as a single stereo-isomer. A one-step oxidative conversion of all three diol functionalities to lactone moieties generated three out of the four possible porphotrilactone regioisomers that were spectroscopically and structurally characterized. This conversion recovered most of the porphyrinic macrocycle aromatic ring current, as seen in their 1H NMR spectra and modeled using DFT computations. Stepwise OsO4-mediated dihydroxylations of porpho-mono- and -di-lactones generated intermediate oxidation state compounds between the pyrrole-three pyrroline macrocycle of the pyrrocorphin and the pyrrole-three oxazolone chromophore of the trilactones. The aromaticity of these chromophores was reduced with increasing number of oxazolone to pyrroline replacements, showing the importance for the presence of three lactone moieties for the retention of the macrocycle aromaticity in the tris-β,β′-modified macrocycles. This work first describes hexahydoxypyrrocorphins, porphotrislactones, and the oxidation state intermediates between them; furthers the understanding of the roles of β-lactone moieties in the expression of porphyrinic macrocycle aromaticity; and generally broadens access to chemically stable pyrrocorphins and pyrrocorphin analogues.

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Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin

Bhattacharya,

Nevonen,

Auty

et al. 2023

J. Phys. Chem. A

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The introduction of three β-oxosubstituents to octaethylporphyrin by means of an oxidation/rearrangement reaction generates the trioxopyrrocorphin chromophore. Pyrrocorphins (hexahydroporphyrins) are generally nonaromatic, but we recently demonstrated trioxopyrrocorphins to possess considerable aromatic character. This contribution explores the photophysical characteristics of these unusual chromophores. In agreement with density functional theory modeling, the UV–vis and magnetic circular dichroism spectra of the twoout of the four possibletriketone regioisomers investigated conform to the Gouterman model of porphyrinoid optical spectra, in alignment with their aromaticity. Their excited-state dynamics shed further light on the degree to which β-oxo substitutions tune the photophysical properties of porphyrinoids. Introduction of β-oxo functionalities increases the rate and yield of intersystem crossing and shortens the triplet state lifetime. Unexpectedly, the singlet oxygen generation yield of both pyrrocorphins remains relatively high, with modes of distortion from planarity likely enhancing triplet energy transfer. This work thus expands our understanding of a rare class of porphyrinoids and further characterizes them as sustaining aromatic porphyrinic π-systems. Our findings suggest triple β-oxo substitution as a viable route toward the development of novel, high-singlet oxygen yield porphyrinic photosensitizers.

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β-Trioxopyrrocorphins: pyrrocorphins of graded aromaticity

Abstract: The four possible pyrrocorphin isomers were prepared. Remarkably, they show regiochemically dependent aromaticity attributed to the presence of a 16-membered, 18 π-electron aromatic ring-current.

Cited by 6 publications

References 66 publications

Stepwise Reduction of β-Trioxopyrrocorphins: Collapse of the Oxo-Induced Macrocycle Aromaticity

Stepwise Reduction of β-Trioxopyrrocorphins: Collapse of the Oxo-Induced Macrocycle Aromaticity

Syntheses and Aromaticity Parameters of Hexahydroxypyrrocorphin, Porphotrilactones, and Their Oxidation State Intermediates

Photophysical Exploration of Two Isomers of Octaethyltrioxopyrrocorphin

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