- Oxidative Dephosphorylation of Benzylic Phosphonates with Dioxygen Generating Symmetrical trans-Stilbenes
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Under a dioxygen atmosphere, benzylphosphonates and related phosphoryl compounds can readily produce the corresponding trans-stilbenes in high yields with high selectivity upon treatment with bases. Various functional groups were tolerable under the reaction conditions.
- Huang, Tianzeng,Chen, Tieqiao,Han, Li-Biao
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p. 2959 - 2965
(2018/03/09)
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- Direct Conversion of Alcohols into Alkenes by Dehydrogenative Coupling with Hydrazine/Hydrazone Catalyzed by Manganese
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We have developed unprecedented methods for the direct transformation of primary alcohols to alkenes in the presence of hydrazine, and for the synthesis of mixed alkenes by the reaction of alcohols with hydrazones. The reactions are catalyzed by a manganese pincer complex and proceed in absence of added base or hydrogen acceptors, liberating dihydrogen, dinitrogen, and water as the only byproducts. The proposed mechanism, based on preparation of proposed intermediates and control experiments, suggests that the transformation occurs through metal–ligand cooperative N?H activation of a hydrazone intermediate.
- Das, Uttam Kumar,Chakraborty, Subrata,Diskin-Posner, Yael,Milstein, David
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supporting information
p. 13444 - 13448
(2018/09/14)
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- A highly stereoselective and efficient catalytic approach for the synthesis of trans-stilbene–arenes as π-conjugated materials
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The potential expansion of the variety of catalytic methods for carbon–carbon bond formation is explored in many research centers all over the world. In this work, we describe very precise and controlled catalytic transformations as useful tools for the synthesis of new trans-π-conjugated molecular organic compounds. The combination of Suzuki–Miyaura coupling and cross-metathesis reactions is established as a simple and efficient method for the design of new (E)-stilbenes in the presence of well-defined transition-metal catalysts at 0.0001–1 % loadings. All of the desired products are isolated in good-to-excellent yields (up to 96 % isolated yield) with high purity.
- Majchrzak, Mariusz,Wilkowski, Grzegorz,Kubicki, Maciej
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p. 4291 - 4299
(2018/10/05)
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- Reductive coupling of aldehydes by H2S in aqueous solutions, a C-C bond forming reaction of prebiotic interest
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We report here a novel reductive coupling reaction of conjugated, non- or poorly enolizable aldehydes induced by H2S and operative in aqueous solutions under prebiotically relevant conditions. This reaction leads from retinal to β-carotene, and from benzylic aldehydes to the corresponding diarylethylenes. This novel reaction also opens a new potentially prebiotic pathway leading from glyoxylic acid to various compounds that are involved in the reductive tricarboxylic acid cycle. This C-C bond forming reaction of prebiotic interest might have been operative, notably, in the sulfide-rich environments of hydrothermal vents, which have been postulated as possible sites for the first steps of organic chemical evolution.
- Kajjout, Mohammed,Hebting, Yanek,Albrecht, Pierre,Adam, Pierre
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experimental part
p. 714 - 726
(2012/07/14)
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- A new efficient synthesis of the stilbenoid laser dyes BPS and Stilbene i by palladium-catalyzed coupling of ethene with bromoarenes
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The palladium-catalyzed coupling of ethene with 4-bromobi phenyl and 4′-bromo-4-biphenylsulfonic acid permits a facile one-pot preparation of the laser dyes (E)-4,4′-diphenylstil bene (BPS, 3) and bis (trie thylammonium) (E)-4,4′-diphenyl-stilbene-4″,4?-disulfonate (6) in diastereomerically pure form on a multigram scale, with yields of 69 and 64%, repectively. The latter can easily be transformed to its dipotassium salt 7, the Stilbene I dye. VCH Verlagsgcscllschaft mbH,.
- Ruemper, Joerg,Sokolov, Viktor V.,Rauch, Rarsten,De Meijere, Armin
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p. 1193 - 1195
(2007/10/03)
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- Fluorescence Emission of trans-4,4'-Diphenylstilbene
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The fluorescence quantum yields of trans-4,4'-diphenylstilbene have been measured in solvents of different polarities using anthracene as the fluorescence standard, and compared with quantum yields of isomerisation in these solvents.The fluorescence emission is quenched by compounds containing heavy atoms.From the Stern-Volmer plots for quenching by propyl bromide, methylene dibromide and tetrabromoethylene, the bimolecular quenching rate constants (kq) are calculated as 2.03E7, 1.05E8 and 7.45E8 dm3mol-1S-1, respectively. kq is found to be proportional to n5/2, where n is the number of bromine atoms in the quencher molecule. kq values for methylene dibromide amd methylene diiodide are in the ratio 1:100.This is approximately related to the sixth power of spin-orbital coupling factors of bromine and iodine atoms.
- Kunjappu, Joy T.,Rao, K. N.
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- Photoisomerisation of trans-4,4'-Diphenylstilbene
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The photoisomerisation of trans-4,4'-diphenylstilbene, a laser dye for the blue region of electromagnetic spectrum, is carried out at 350 nm and 300 nm in benzene, dioxane and mixtures of benzene and methanol.The effects of photon intensity and concentration of the dye on the isomerisation process have been investigated in deaerated benzene solutions at 350 nm.The first order rate constants for the isomerisation of the trans-form have been determined .The photostationary equilibrium (PSE) concentration of the cis and trans isomers is also reported.The results are explained by Saltiel's twisted singlet excited state mechanism.The rate data under increasing solvent polarities indicate that the trans-singlet state crosses over more easily into the common twisted singlet form than the corresponding cis-singlet state.Also, the PSE shifts towards the cis-isomer at higher solvent polarities.
- Kunjappu, Joy T.,Rao, K. N.
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p. 636 - 640
(2007/10/02)
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- Electron Transfer Induced Isomerization of cis-4,4'-Diphenylstilbene into Its Trans Form
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The 4,4'-diphenylstilbenes, denoted by C and T for the cis and trand isomers, as well as T-. and T2-, were characterized spectroscopically and electrochemically.The disproportionation 2T-.,Na+ T + T2-,2Na+ has equilibrium constant in THF 0.04, ΔH = 18.2 kcal/mol, and ΔS = 54 cal/moldeg, and its rate constant is 9.0 108 M-1 s-1.The cis-trans isomerization was studied in THF at ambient temperature in three systems: T + T-.,Na+ + C, T2-,2Na+ + C, and B-.,Na+ + C, B denoting biphenyl.In the first two systems the reaction is governed by the three interrelated equilibria, namely, C + T-.,Na+ T + C-.,Na+ (K1), C + T2-,2Na+ C-.,Na+ + T-.,Na+, (K2 = K1/Kdispr), and 2T-.,Na+ T + T2-,2Na+ (Kdispr), the rate-determining step being C-.,Na+ -> T-.,Na+ (ki).The results give kiK1 or kiK2.In the last system the rapid electron transfer B-.,Na+ + C -> B + C-.,Na+ produces momentarily high concentration of C-.,Na+ and, since its disproportionation is favored, a relatively large amount of C2-,2Na+.The latter rapidly isomerizes into T2-,2Na+.Thus, in early stages of the reaction, the concentration of T2-,2Na+ exceeds that expected for the disproportionation equilibrium had the reaction with B-.,Na+ formed only C-.,Na+ and then T-.,Na+.This observation provides the evidence for the existence of C2-,2Na+.
- Chien, C. K.,Wang, H. C.,Szwarc, M.,Bard, A. J.,Itaya, K.
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p. 3100 - 3104
(2007/10/02)
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