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

Meehan, Eileen; Li, Ruoshi; Zeller, Mat­thias; Brückner, Christian

doi:10.1021/acs.orglett.5b00800

Cited by 16 publications

(15 citation statements)

References 49 publications

(45 reference statements)

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“…Expanding on our earlier communication, we present herein the full details of the surprising outcomes of applying Beckmann‐rearrangement conditions to oxochlorin oxime 8 (and 8Ni ). The reaction of free base 8 yields an 1,3‐oxazine‐based PMP lactone, formed by an abnormal Beckmann rearrangement and subsequent reactions.…”

Section: Introductionmentioning

confidence: 90%

Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 2. Beckmann‐Rearrangement Conditions

Meehan

Zeller

et al. 2017

Eur J Org Chem

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The step‐wise conversion of synthetic porphyrins to derivatives that contain a non‐pyrrolic building block is an appealing method to generate functionalized porphyrinoids. Applied to octaethyloxochlorin oxime, a Beckmann rearrangement is potentially suited to generate a nitrogen‐expanded porphyrinoid. Unexpectedly, this reaction led to a ring‐expansion by an oxygen atom. The mechanism – an abnormal Beckmann reaction, followed by an intramolecular ring‐closing reaction and hydrolysis – was conclusively derived by trapping and structural characterization of the key secochlorin intermediate. The structural and UV/Vis spectral changes observed upon ring‐expansion of the oxochlorin are discussed. Other Beckmann‐rearrangement conditions failed to produce ring‐expanded products altogether. This work demonstrates in many ways how the extraordinary structural stability of the porphyrin macrocycle redirects the reactivity patterns of classic ring‐expansion reactions, which outlines the limits of the “breaking and mending of porphyrins” approach toward pyrrole‐modified porphyrins.

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Section: Introductionmentioning

confidence: 90%

Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 2. Beckmann‐Rearrangement Conditions

Meehan

Zeller

et al. 2017

Eur J Org Chem

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“…A CSD search (Version 5.41 with updates up to May 2020; Groom et al, 2016) for porphyrinic macrocyles of three pyrroles and a single six-membered ring while retaining the porphyrin-like architecture of four central nitrogen atoms reveals 24 structures: six pyriporphyrins (i.e., porphyrinoids containing a pyridine building block), fifteen morpholinochlorins, two thiomorpholines [UCIKOJ and UCILIE (Sharma et al, 2016)], and a single 1,3-oxazinochlorin (WUDMIT; Meehan et al, 2015). Among the 1,4morpholinochlorins, six are free base structures, the remainder are metal complexes [of Cu II , Ni II -most frequently, Zn II , Ag II and Pd II , see…”

Section: Database Surveymentioning

confidence: 99%

Crystal structure of 2,3-dimethoxy-meso-tetrakis(pentafluorophenyl)morpholinochlorin methylene chloride 0.44-solvate

et al. 2020

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The title morpholinochlorin, C46H16F20N4O3, was crystallized from hexane/methylene chloride as its 0.44 methylene chloride solvate, C46H16F20N4O3·0.44CH2Cl2. The morpholinochlorin was synthesized by stepwise oxygen insertion into a porphyrin using a `breaking and mending strategy': NaIO4-induced diol cleavage of the corresponding 2,3-dihydroxychlorin with in situ methanol-induced, acid-catalyzed intramolecular ring closure of the intermediate secochlorins bisaldehyde. Formally, one of the pyrrolic building blocks was thus replaced by a 2,3-dimethoxymorpholine moiety. Like other morpholinochlorins, the macrocycle of the title compound adopts a ruffled conformation, and the modulation of the porphyrinic π-system chromophore induces a red-shift of its optical spectrum compared to its corresponding chlorin analog. Packing in the crystal is governed by interactions involving the fluorine atoms of the pentafluorophenyl substituents, dominated by C—H...F interactions, and augmented by short fluorine...fluorine contacts, C—F...π interactions, and one severely slipped π-stacking interaction between two pentafluorophenyl rings. The solvate methylene chloride molecule is disordered over two independent positions around an inversion center with occupancies of two × 0.241 (5) and two × 0.199 (4), for a total site occupancy of 88%.

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“…Most β‐alkylporphyrin‐derived PMPs were prepared by total synthesis,[2d], [2f], but some have also been synthesized by the conversion of octaethylporphyrin (OEP, 1 ). Examples include oxazolochlorin 2 , or the PMPs 3 [1a], and 4 that contain six‐membered rings. Other exotic pathways towards PMPs are also known; for instance, chlorophin 5 was formed by serendipity as the product of an oxidation and subsequent rearrangement of a [hydrocorrinato]Ni II complex …”

Section: Introductionmentioning

confidence: 99%

“…Parallel to the mechanistic considerations controlling the Beckmann reactions,[1a] product 8 is also the more likely product of a Schmidt‐reaction pathway in comparison to 7 . However, as multiple examples have shown, the steric restrictions of the porphyrin ring can alter the expected outcomes of classic reactions , …”

Section: Introductionmentioning

confidence: 99%

Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 3. Schmidt‐Reaction Conditions

Zeller

Bruhn

et al. 2017

Eur J Org Chem

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The Schmidt reaction (treatment of a ketone with sodium azide and a mineral acid) is an alternative to the Beckmann rearrangement to expand a cyclic ketone to a lactam. However, when applied toward the conversion of a synthetic porphyrin into a derivative containing a nonpyrrolic building block, this approach failed to generate the expected lactam. Instead, by using sulfuric acid as a catalyst, a novel heptaethyl‐2‐hydroxy‐chlorin‐3‐one was formed, structurally characterized, and its mechanism of formation deduced. The work demonstrates how the extraordinary structural stability of the porphyrin macrocycle redirects the reactivity patterns of classic ring‐expansion reactions. By using hydrochloric acid as a catalyst, a somewhat regioselective chlorination of the meso‐positions of the oxochlorin was observed. The halogenation sites were determined spectroscopically and by X‐ray crystallography of selected derivatives. The regioselectivity of the halogenation was computationally rationalized. This method is superior to alternative halogenation methods for the regioselective generation of 5‐chloro‐, 10‐chloro‐, and 5,10‐dichlorooxochlorins.

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

Cited by 16 publications

References 49 publications

Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 2. Beckmann‐Rearrangement Conditions

Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 2. Beckmann‐Rearrangement Conditions

Crystal structure of 2,3-dimethoxy-meso-tetrakis(pentafluorophenyl)morpholinochlorin methylene chloride 0.44-solvate

Surprising Outcomes of Classic Ring‐Expansion Conditions Applied to Octaethyloxochlorin, 3. Schmidt‐Reaction Conditions

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