Regioselectivity and stereoselectivity in the photodimerization of rigid and semirigid stilbenes

Wolff, Thomas; Schmidt, F. W.; Volz, Peter

doi:10.1021/jo00041a035

Cited by 18 publications

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“…The 'H NMR spectrum of the trans-syrz-trans dimer 6 shows a multiplet at 6 -4.4 ppm, which is characteristic of trans-syn-trans stereochemistry in stilbene photodimers (15). The spectra of the all-trans dimers 7a and 8a,b show characteristic resonances at 6 -3.7 ppm (16,17). The identities of the isomers 7a and 8a were established on the basis of their mass spectral fragmentation patterns (18); that of 8b was analogous to that of 8a.…”

Section: Resultsmentioning

confidence: 97%

“…Unfortunately, the methoxy singlets are too closely spaced in the 500 MHz spectrum of 10c to allow meaningful information to be gleaned from analogous experiments in this case. Identification of the cyclobutane dimers 6-8 was made on the basis of their 'H NMR and mass spectra (15,16). The 'H NMR spectrum of the trans-syrz-trans dimer 6 shows a multiplet at 6 -4.4 ppm, which is characteristic of trans-syn-trans stereochemistry in stilbene photodimers (15).…”

Section: Resultsmentioning

confidence: 99%

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The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

Leigh¹,

Lewis²,

Lin³

et al. 1996

Can. J. Chem.

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The photochemistry of the title compounds has been investigated in ethanol and tetrahydrofuran solution under aerobic and anaerobic conditions. Direct irradiation of trans-3,3',4,4'-tetramethoxystilbene (tra~zs-1) in deoxygenated ethanol leads to the rapid establishment of a photostationary state with the cis isomer, and the slower formation of the ethyl ether corresponding to addition of ethanol across the olefinic C=C bond and cyclobutane dimers. The same products are formed upon photolysis in the presence of oxygen under the same conditions but, in addition, two isomeric tetramethoxyphenanthrenes and 3,4-dimethoxybenzaldehyde are formed. Photolysis of trans-1 in oxygenated tetrahydrofuran leads to the same products in different relative yields. Quantum yields for cis,rra~ls photoisomerization, phenanthrene formation, and addition of ethanol have been determined by ferrioxalate actinometry. Direct irradiation of trans-4-hydroxy-3,3',4'-trimethoxystilbene (tratls-2) in ethanol solution also results in rapid cis-tra~ls isomerization and the formation of (three) isomeric phenanthrene derivatives in photolyses carried out in the presence of oxygen, although the material balance is low. The various products of photolysis of trans-2 have been independently synthesized by desilylation of the products isolated from photolysis of trclns-4-tertbutyldimethylsiloxy-3,3',4'-trimethoxystbene (trans-3) under similar conditions. Fluorescence-quenching experiments have been carried out to determine the relative rates of quenching of the excited singlet states of trans-1 and tmtzs-2 by alcohols and oxygen. The formation of aldehydes is proposed to arise via reaction of superoxide ion with stilbene radical cations, which are formed by electron-transfer quenching of the stilbene excited singlet state by oxygen.Key words: stilbenes, lignin, photochemistry, photooxidation.RCsumC : On a CtudiC la photochimie des composCs mentionnks dans le titre en solutions dans 1'Cthanol et le titrahydrofurane, dans des conditions tant akrobiques qu'anakrobiques. L'irradiation direct du tmtzs-3,3',4,4'-tCtramkthoxystilbkne (tratzs-1) dans de 1'Cthanol dCsoxygCnC conduit h la crCation rapide d'un Ctat photostationnaire avec l'isomere cis et h une formation plus lente de l'tther Cthylique correspondant ii l'addition de 1'Cthanol sur la double liaison C=C olCfinique ainsi que des dimkres cyclobutanes. Les m&mes produits se forment lors de la photolyse dans les m&mes conditions, en prCsence d'oxygkne; toutefois, il se forme de plus deux tCtramtthoxyphCnanthrbnes isomkres ainsi que du 3,4-dimCthoxybenzaldthyde. La photolyse du tratzs-1 dans du titrahydrofurane oxygCnC conduit h la formation des m&me produits avec des rendements relatifs diffkrents. On a dCterminC les rendements quantiques de la photoisomCrisation cis, trans, de la formation du phknanthrkne et de l'addition de l'tthanol par actinomCtrie feriioxalate. L'irradiation directe du tmrzs-4-hydroxy-3,3',4'-trimCthoxystilbbne (trans-2) en solution dans 1'Cthanol effectuke en prtsence ...

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

Leigh¹,

Lewis²,

Lin³

et al. 1996

Can. J. Chem.

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“…Grafted samples were exposed to 2 M aqueous HCl, dried, and irradiated through a mask using the apparatus described above for photochemical grafting for 2 h. The light was filtered through a 320-nm cutoff filter in order to prevent the photochemical back reaction of phenylindene photodimers [11]. Thereafter the sample was exposed to toluene, dried, and irradiated without the mask for 2 h.…”

Section: Photochemical Structuringmentioning

confidence: 99%

“…More- over, in selective irradiation of certain surface areas through a mask, the defined crosslinking is restricted to the irradiated parts, while radical-induced crosslinking might extend somewhat into nonirradiated areas. As a photodimerizable moiety we chose phenylindene, whose photodimerization was investigated previously in detail [11]. Polystyrene containing phenylindene moieties (cf.…”

Section: Introductionmentioning

confidence: 99%

Photochemical structuring and fixing of structures in binary polymer brush layers via photodimerization

Hoffmann¹,

Wolff²,

Minko³

et al. 2005

Journal of Colloid and Interface Science

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“…It was concluded that the reaction proceeds through the triplet state of the DBA thereby differing from other stilbenes which undergo dimerization upon direct irradiation, that is, through the singlet excited state. [3,4] Moreover, only N-acyl derivatives, such as N-acetyl (10) and N-propionyl DBA (14) [1, 2,5] or the pharmaceutically active N-carbamoyl compound ™carbamazepine∫ (21), were found to photodimerize.…”

Section: Introductionmentioning

confidence: 99%

Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

Querner

Wolff

Görner

2003

Chemistry A European J

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The photoprocesses of a series of N-substituted dibenz[b,f]azepines (iminostilbenes) were studied by absorption and emission spectroscopy, by laser flash photolysis, and by preparative irradiation with NMR analysis. In solutions, 2pi+2pi photodimers of N-cyano and N-acyl dibenzazepines are formed via the triplet state upon acetone- or benzophenone-sensitized energy transfer. T-T absorption spectra were measured and absorption coefficients were determined. The triplet energy transfer is equally efficient for N-alkyl dibenzazepines, which do not dimerize. Excited states of npi* character in the latter cases are discussed to rationalize the different reactivities. In spite of negligible intersystem crossing of 21 dibenzazepine derivatives, photodimers of N-acyl and N-cyano dibenzazepines are formed upon direct excitation in concentrated solutions (0.01-0.1 mol dm(-3)) as well as in the solid state. A selective anti-configuration of the photodimers was found throughout.

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Regioselectivity and stereoselectivity in the photodimerization of rigid and semirigid stilbenes

Cited by 18 publications

References 0 publications

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

The photochemistry of 3,3′,4,4′-tetramethoxy-and 4-hydroxy-3,3′,4′-trimethoxystilbene — models for stilbene chromophores in peroxide-bleached, high-yield wood pulps

Photochemical structuring and fixing of structures in binary polymer brush layers via photodimerization

Substituent‐Dependent Reactivity in the Photodimerization of N‐Substituted Dibenz[b,f]azepines

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