- Dihedral-Angle-Controlled Crossover from Static Hole Delocalization to Dynamic Hopping in Biaryl Cation Radicals
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In cases of coherent charge-transfer mechanism in biaryl compounds the rates follow a squared cosine trend with varying dihedral angle. Herein we demonstrate using a series of biaryl cation radicals with varying dihedral angles that the hole stabilization
- Talipov, Marat R.,Navale, Tushar S.,Hossain, Mohammad M.,Shukla, Ruchi,Ivanov, Maxim V.,Rathore, Rajendra
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p. 266 - 269
(2016/12/30)
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- A simple method for the synthesis of furfuryl ketones and furylacetic acid derivatives
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A simple preparative method has been developed for the synthesis of aryl(furfuryl) ketones, amides, and furylacetic acid esters, based on radical alkylation of furan derivatives at the α-position with O-ethyl(phenacyl)xanthogenates and phenacyl iodides in the presence of Fenton's reagent (H2O2/FeSO4·7H2O) in DMSO. The range of applicability and mechanisms for the formation of major and side products have been considered.
- Chalikidi, Petrakis N.,Nevolina, Tatyana A.,Uchuskin, Maxim G.,Abaev, Vladimir T.,Butin, Alexander V.
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p. 621 - 629
(2015/10/12)
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- Photochemistry of S -phenacyl xanthates
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Various synthetically readily accessible S-phenacyl xanthates are shown to undergo photoinitiated homolytic scission of the C-S bond in the primary step. The resultant fragments, phenacyl and xanthic acid radicals, recombine to form symmetrical 1,4-diketones and xanthogen disulfides, respectively, in high to moderate chemical yields in chemically inert solvents. They can also be efficiently trapped by a hydrogen-atom-donating solvent to give acetophenone and xanthic acid derivatives. The latter compound is in situ thermally converted to the corresponding alcohol in high chemical yields. S-Phenacyl xanthates could thus be utilized as synthetic precursors to the above-mentioned compounds or as photoremovable protecting groups for alcohols in which the xanthate moiety represents a photolabile linker. The photochemically released phenacyl radical fragments efficiently but reversibly add to the thiocarbonyl group of the parent xanthate molecule. The kinetics of this degenerative reversible addition-fragmentation transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) mechanism was studied using laser flash photolysis (LFP) and density functional theory (DFT) calculations. The rate constants of the RAFT addition step, kadd ~ 7 × 108 M-1 s-1, and phenacyl radical addition to a double bond of 1,1-diphenylethylene, kadd ~ 108 M-1 s -1, in acetonitrile were experimentally determined by LFP. In addition, photoinitiation of the methyl methacrylate polymerization by S-phenacyl xanthate is demonstrated. The polydispersity index of the resulting poly(methyl methacrylate) was found to be ~1.4. We conclude that S-phenacyl xanthates can serve simultaneously as photoinitiators as well as RAFT/MADIX agents in polymerization reactions.
- Tazhe Veetil, Aneesh,Solomek, Tomas,Ngoy, Bokolombe Pitchou,Pavlikova, Nela,Heger, Dominik,Klan, Petr
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p. 8232 - 8242
(2012/01/03)
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- Synthesis and trypanocidal activity of 1,4-bis-(3,4,5-trimethoxy-phenyl)-1,4-butanediol and 1,4-bis-(3,4-dimethoxyphenyl)-1,4-butanediol
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Chagas' disease is endemic in Central and South American countries. Specific chemotherapy with nifurtimox or benznidazole has been recommended for treatment of recent infection but they have limited efficacy. The natural products veraguensin (1) and grand
- Bernardes, Lilian Sibelle Campos,Kato, Massuo Jorge,Albuquerque, Sergio,Carvalho, Ivone
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p. 7075 - 7082
(2007/10/03)
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- Substituted furans as inhibitors of the PDE4 enzyme
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The synthesis and in vitro activity of a series of substituted furans as a novel structural class of PDE4 inhibitors is described. Comparison of emetic threshold with known PDE4 inhibitors is presented.
- Perrier, Helene,Bayly, Christopher,Laliberte, France,Huang, Zheng,Rasori, Roberta,Robichaud, Annette,Girard, Yves,Macdonald, Dwight
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p. 323 - 326
(2007/10/03)
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- The Photochemistry of α-Phenoxyacetophenones Investigated by Flash-CIDNP-spectroscopy
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The photochemistry of 14 different substituted α-phenoxyacetophenones (1) was studied by CIDNP-spectroscopy using XeCl excimer laser (308 nm) and a 250 MHz 1H-NMR spectrometer.To characterize the excited states the electronic absorption and emission spectra as well disappearance quantum yields were investigated also. - Two reaction channels were established: 1) β-cleavage from the singlet state; and 2) the formation of acetophenones via the respective enol forms where the origin of the polarization remains unclear.It is concluded that these are the main reaction channels, since all products formed show polarizations in the CIDNP-spectr a. - In contrast to the current assumptions for the typical acetophenone reaction of (1) leading to the β-cleavage, we are led to interprete the CIDNP-spectra of (1) as a result of a reaction due to the phenoxy part with all characteristics of a photo-Claisen reaction. Keywords: Luminescence / Photochemistry / Radicals / Spectroscopy, CIDNP / Spectroscopy, Nuclear Magnetic Resonance / Spectroscopy, Ultraviolet
- Palm, W.-U.,Dreeskamp, H.,Bouas-Laurent, H.,Castellan, A.
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- Photodegradation of the lignin model α-guaiacoxyacetoveratrone, unusual effects of solvent, oxygen, and singlet state participation
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α-Guaiacoxyacetoveratrone, a lignin model compound, has been studied using a combination of laser flash photolysis and steady state quantum yields.Triplet lifetimes range from 175 to 600 ns while the quantum yields of photodegradation vary from 0.06 to 0.6, depending on the solvent.Singlet processes (Φ ca. 0.1), previously unobserved for aromatic ketones, are implicated in the mechanism, and account for most or all of the degradation in aprotic solvents. Key words: photodegradation, α-guaiacoxyacetoveratrone.
- Schmidt, John A.,Berinstain, Alain B.,Rege, Francis de,Heitner, Cyril,Johnston, Linda J.,Scaiano, J. C.
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p. 104 - 107
(2007/10/02)
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- Reactions of carbanions from 2-(dialkylamino)-arylacetonitriles with acetylene - Simple syntheses of 1,3-dienamines and 1,4-diketones
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It has been found that morpholinonitrile 1a reacts with acetylene (2) in the presence of solid sodium hydroxide and tetrabutylammonium bromide (TBABr) as a catalyst, in DMSO, to give the vinyl derivative 3a. Whereas aminonitriles 1b-i, in the reaction with 2, afford dienamines 7. The different reactivity of 1a as compared to 1b-i is explained in terms of the different basicity of the amino moiety in vinyl derivatives 3. Dienamines 7 were hydrolyzed to 1,4-diarylbutan-1,4-diones 8 in high yields.
- Jonczyk, Andrzej,Lipiak, Dariusz,Zdrojewski, Tadeusz
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p. 1025 - 1038
(2007/10/02)
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- 2,5-diaryl tetrahydrothiophenes and analogs thereof as PAF-antagonists
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Analogs of 2,5-Diaryl tetrahydrothiophenes which were substituted or unsubstituted on 3,4-positions were prepared. These compounds are found to be leukotriene inhibitors and potent and specific PAF (Platelet Activating Factor) antagonists. They are th
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- 2,5-Diaryl tetrahydrofurans and analogs thereof as PAF-antagonists
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Analogs of 2,5-Diaryl tetrahydrofurans which were substituted or unsubstituted at 3,4-positions were prepared. These compounds are found to have potent and specific PAF (Platelet Activating Factor) antagonistic activities and thereby useful in the tre
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