Intramolecular photochemical hydrogen abstraction in 2-alkylpyrazines and 2-alkylpyridines

Mukherjee, Ashis K.; Duggan, Sandhya A. M.; Agosta, William C.

doi:10.1021/jo00080a029

Cited by 10 publications

(5 citation statements)

References 2 publications

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“…The first stage of the reaction is a hydrogen‐atom abstraction from a solvent by the pyridine nitrogen atom. The second stage is a replacement of a ring hydrogen by strong nucleophilic alkyl radicals (Scheme ) .…”

Section: Resultsmentioning

confidence: 99%

“…In the photo‐Beckmann rearrangement the excited oxime ( E or Z‐i somer) transforms into an oxaziridine intermediate, which reorganizes to an appropriate amide. In the photosubstitution reaction, the first step is probably the pyridyl radical formation through the hydrogen abstraction from the solvent and next, the photosubstitution by the heptyl or benzyl radicals (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

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Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

Wieszczycka

Zembrzuska

2015

Photochem & Photobiology

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The goal of the research was to study the reactivity of the hydrophobic 2- and 3-pyridineketoximes under exposure to UV-VIS light. The photodegradation was conducted in both toluene and heptane for 10 h under atmosphere of argon. Ten-hour irradiation experiments demonstrated that the pyridineketoximes underwent the facile E-Z photoisomerization, photo-Beckmann rearrangement, and to a lesser extent, the photosubstitution to the pyridine ring. From LC-MS and NMR analysis of the irradiated solutions, it was found that the photosubstitution proceeded to give the corresponding 6-substituted 2- or 3-pyridylketoxime via the replacement of the ring hydrogen by the benzyl or heptyl group. The photo-Beckmann rearrangement led to the formation of the corresponding amides, but also other products formed in the photo-decomposition reaction.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

Wieszczycka

Zembrzuska

2015

Photochem & Photobiology

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“…Moreover, the high absorptivity of TBADT at the wavelength used prevented the light absorption of the starting vinylpyridines (see Figures S1 and S2 in the Supporting Information) and of the end compounds. This was beneficial to the overall process because it again avoided a photopolymerization of 2 and at the same time made intramolecular hydrogen‐abstraction side reactions from the resulting 2‐alkylpyridines negligible . The presence of a COOEt or CN group on the double bond of the vinylpyridines makes them more electrophilic but shifts (at least in part) the regioselectivity of the radical attack to the α‐position.…”

Section: Figurementioning

confidence: 86%

“…2017, 23,6527 -6530 www.chemeurj.org photopolymerization of 2 [17] and at the same time made intramolecular hydrogen-abstraction side reactions from the resulting 2-alkylpyridines negligible. [18] The presence of aC OOEt or CN group on the double bond of the vinylpyridines makes them more electrophilic but shifts (at least in part) the regioselectivity of the radical attack to the a-position.…”

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confidence: 99%

Vinylpyridines as Building Blocks for the Photocatalyzed Synthesis of Alkylpyridines

Capaldo

Fagnoni

Ravelli

2017

Chemistry A European J

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The photocatalyzed addition of several hydrogen donors (ethers, aldehydes, alkanes, amides) onto vinylpyridines was achieved. This approach provided access to alkylpyridines, which are important building blocks for the preparation of compounds with biological activity. The strategy was very simple and straightforward because it required only a small amount of a cheap decatungstate salt as photocatalyst. As an added advantage, the reaction could be performed under sunlight irradiation as well as under flow conditions.

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“…Sugiyama et al [28], Minisci [30] and Citterio et al [31] pointed out that photoalkylation to the pyridine ring or to other aromatic N-heterocycles occurs through hydrogen abstraction by the excited protonated pyridine derivatives, while the addition of mineral acids caused the alkylation to 4-position (exciting pyridinium form) and the alkoxylation to 6-position resulting in excimer formation. In the case the oxime of alkyl -3-and -4-pyridyl ketone methoxy photosubstitution, the hydrogen migration is probably favored by the protic solvent [32]. A similar mechanism causes methyl substitution through the reduction of the hydroxyalkyl fragment.…”

Section: By-products Analysismentioning

confidence: 99%

Photodegradation of pyridylketoximes in methanolic solutions under UV–Vis radiation

2012

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Photodegradation of the oximes of alkyl-2- ,-3-, and-4-pyridylketones and identification of possible degradation products using LC-MS/MS and GC-MS techniques were performed. The influence of copper(II) and iron(III) ions on the stability of the oxime under UV-Vis radiation exposure were also studied. It was found that the photodegradation of the pyridylketoximes resulted in the photoisomerization, photofragmentation and photosubstitution to a pyridine ring. Based on these results, a hypothetical mechanism of photodegradation of pyridylketoximes was proposed.

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Intramolecular photochemical hydrogen abstraction in 2-alkylpyrazines and 2-alkylpyridines

Cited by 10 publications

References 2 publications

Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

Photodegradation of Hydrophobic Pyridineketoximes in Toluene and Heptane

Vinylpyridines as Building Blocks for the Photocatalyzed Synthesis of Alkylpyridines

Photodegradation of pyridylketoximes in methanolic solutions under UV–Vis radiation

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