Free Radicals Produced from the Derivatives of Pyrylium Salts in Solution by Photoillumination

Niizuma, Shigeya; Sato, Nobuyoshi; Kawata, Hiroki; Suzuki, Yoshizo; Toda, Takashi; Kokubun, Hiroshi

doi:10.1246/bcsj.58.2600

Cited by 33 publications

(18 citation statements)

References 4 publications

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“…This hyperfine coupling (hfc) structure could be reproduced through simulation (Figure S15A) and was in complete agreement with previously reported hfc constants for that compound. 25 Moreover, the formation of 1b • was confirmed with UV–visible absorption spectroscopy (Figure S21A). 25b By contrast, no hyperfine splitting structure was observed for the analogous system containing 1a and 2a , even when a low-amplitude modulation was used ( M = 0.08 G).…”

Section: Resultsmentioning

confidence: 81%

“…25 Moreover, the formation of 1b • was confirmed with UV–visible absorption spectroscopy (Figure S21A). 25b By contrast, no hyperfine splitting structure was observed for the analogous system containing 1a and 2a , even when a low-amplitude modulation was used ( M = 0.08 G). 27 However, this absence of hyperfine structure was noted by Kawata and colleagues 26 and could be due to a broadening induced by the Heisenberg exchange effect.…”

Section: Resultsmentioning

confidence: 81%

“…27 However, this absence of hyperfine structure was noted by Kawata and colleagues 26 and could be due to a broadening induced by the Heisenberg exchange effect. 28 To unambiguously attribute the signal arising from the irradiation of 1a and CTA 2a to pyranyl radical 1a • , we used THF, a known sacrificial electron donor, 25,26 in lieu of CTA 2a (Figure S16). A comparison of these results with the spectrum in Figure 10 corroborates the suggested formation of pyranyl radical 2a in the reaction conditions.…”

Section: Resultsmentioning

confidence: 99%

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Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers

et al. 2017

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The mechanism of the recently reported photocontrolled cationic polymerization of vinyl ethers was investigated using a variety of catalysts and chain-transfer agents (CTAs) as well as diverse spectroscopic and electrochemical analytical techniques. Our study revealed a complex activation step characterized by one-electron oxidation of the CTA. This oxidation is followed by mesolytic cleavage of the resulting radical cation species, which leads to the generation of a reactive cation–this species initiates the polymerization of the vinyl ether monomer–and a dithiocarbamate radical that is likely in equilibrium with the corresponding thiuram disulfide dimer. Reversible addition–fragmentation type degenerative chain transfer contributes to the narrow dispersities and control over chain growth observed under these conditions. Finally, the deactivation step is contingent upon the oxidation of the reduced photocatalyst by the dithiocarbamate radical concomitant with the production of a dithiocarbamate anion that caps the polymer chain end. The fine-tuning of the electronic properties and redox potentials of the photocatalyst in both the excited and the ground states is necessary to obtain a photocontrolled system rather than simply a photoinitiated system. The elucidation of the elementary steps of this process will aid the design of new catalytic systems and their real-world applications.

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Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 81%

Section: Resultsmentioning

confidence: 99%

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Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers

et al. 2017

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“…In all cases, the major products are 4H-pyrans. The one-electron reduction of them when treated with zinc dust [24][25][26] in a degassed aprotic solvent gives the bichalcogenopyran derivatives via the pyranyl radical intermediates. We have previously described that the LiAlH 4 reduction of the 1-benzotelluropyrylium salts 11) and 1-benzoselenopyrylium salts, 14) the regioisomers of the title compounds, afforded a mixture of the corresponding 2H-and 4H-chromenes, respectively; the latter was the major product.…”

Section: Resultsmentioning

confidence: 99%

“…These bisisochromenyl compounds (3) would be produced by the homo-coupling of the radical intermediates. [24][25][26] Reaction of Pyrylium Salts with Nucleophiles We have recently found that both the 1-benzotelluropyrylium 11) and 1-benzoselenopyrylium salts 14) were attacked by a methoxide ion in MeOH to form the corresponding 4-methoxy-4H-chromenes as the major products in high yields. Although the telluropyrylium salts did not react with a secondary or tertiary alkoxide in the corresponding alcohol to give any characterizable products, the unsubstituted 1-benzoselenopyrylium salts 14) reacted with NaOi-Pr and KOt-Bu to afford the corresponding the 2-alkoxy-2H-selenochromenes in good yields.…”

Section: Resultsmentioning

confidence: 99%

Studies on Tellurium-Containing Heterocycles. Part 20. Reactions of 2-Benzoselenopyrylium Salts and 2-Benzotelluropyrylium Salts with Nucleophiles: Formation of 1-Functionalized 1H-Isoselenochromenes and 1H-Isotellurochromenes

Sashida

Ohyanagi

2004

CHEMICAL & PHARMACEUTICAL BULLETIN

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Recently, the chemistry of the selenopyrylium [2][3][4] and telluropyrylium salts, [2][3][4][5] six-membered cationic heteroaromatics containing a selenium or tellurium atom, in both fields of organic synthesis and the chemical transformation of organotellurium and organoselenium compounds, has attracted considerable attention. Both of the monocyclic pyrylium 6,7) and 1-benzopyrylium salts [8][9][10] containing these atoms have been prepared, and the chemistry of these compounds has been reviewed. We have also previously reported the practical and facile preparation [11][12][13] and the reactions 11,14,15) of these 1-benzopyrylium salts. More recently, we succeeded in preparing 16) the stable 2-benzotelluropyrylium 17) and 2-benzoselenopyrylium salts, 18) structural isomers of them; the former is a previously unknown heterocyclic ring system. Therefore, this paper deals with the results of the examination of the reactivity of these novel 2-benzopyryliun salts with various nucleophiles using the stable compounds, 3-tert-butyl and (or) 3-unsubstituted derivatives as easily available pyrylium salts. The differences in the reactivity of these pyrylium salts containing a tellurium or selenium atom have received most of our attention thus far. Results and DiscussionReduction of Pyrylium Salts 23) were reported. In all cases, the major products are 4H-pyrans. The one-electron reduction of them when treated with zinc dust [24][25][26] in a degassed aprotic solvent gives the bichalcogenopyran derivatives via the pyranyl radical intermediates. We have previously described that the LiAlH 4 reduction of the 1-benzotelluropyrylium salts 11) and 1-benzoselenopyrylium salts, 14) the regioisomers of the title compounds, afforded a mixture of the corresponding 2H-and 4H-chromenes, respectively; the latter was the major product. In order to compare these behaviors, we first examined the hydride reduction of the 2-benzopyrylium salts (1). The reduction of 1A and 1B with LiAlH 4 in diethyl ether at 0°C afforded the 1H-isoselenochromenes (2A) and 1H-isotellurochoromenes (2B) in moderate yields as the sole products, respectively. The use of THF as a solvent almost gave similar results. The pyrylium salts (1) were also reduced by DIBAL-H to give the 1H-isochromenes (2) in quantitative yields. These compounds (2) were identical with the authentic samples, 16) which were the precursors for the synthesis of the corresponding pyrylium salts (1A) and (1B). The 3-tertbutyl-2-benzopyrylium salts (1Aa) and (1Ba) reacted with excess zinc dust in acetonitrile at 0°C under an argon atmosphere to give 1,1Ј-bis(tert-butylisochromenyl) (3Aa) and (3Ba) in 18 and 15% yield as the sole characterized products, respectively. The MS spectrum of compound 3Aa suggested the diselenide molecular formula of C 26 H 30 Se 2 as it measured a molecular ion at m/zϭ502 ( 80 Se) and the expected isotope pattern for Se 2 . The base peak was m/zϭ251, which was a half of the molecular ion. In addition the HR-MS of 3Aa showed the exact molecular formula. There was no c...

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Einelektronenübertragung von Alkoholationen auf 2,4,6‐Triphenyl‐pyrylium‐ und ‐thiopyryliumkationen

Zimmermann

Fischer

Reinhardt

1986

Zeitschrift fuer Chemie

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Free Radicals Produced from the Derivatives of Pyrylium Salts in Solution by Photoillumination

Cited by 33 publications

References 4 publications

Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers

Mechanistic Insight into the Photocontrolled Cationic Polymerization of Vinyl Ethers

Studies on Tellurium-Containing Heterocycles. Part 20. Reactions of 2-Benzoselenopyrylium Salts and 2-Benzotelluropyrylium Salts with Nucleophiles: Formation of 1-Functionalized 1H-Isoselenochromenes and 1H-Isotellurochromenes

Einelektronenübertragung von Alkoholationen auf 2,4,6‐Triphenyl‐pyrylium‐ und ‐thiopyryliumkationen

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