- Energy-Transfer-Mediated Photocatalysis by a Bioinspired Organic Perylenephotosensitizer HiBRCP
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Energy transfer plays a special role in photocatalysis by utilizing the potential energy of the excited state through indirect excitation, in which a photosensitizer determines the thermodynamic feasibility of the reaction. Bioinspired by the energy-transfer ability of natural product cercosporin, here we developed a green and highly efficient organic photosensitizer HiBRCP (hexaisobutyryl reduced cercosporin) through structural modification of cercosporin. After structural manipulation, its triplet energy was greatly improved, and then, it could markedly promote the efficient geometrical isomerization of alkenes from the E-isomer to the Z-isomer. Moreover, it was also effective for energy-transfer-mediated organometallic catalysis, which allowed realization of the cross-coupling of aryl bromides and carboxylic acids through efficient energy transfer from HiBRCP to nickel complexes. Thus, the study on the relationship between structural manipulation and their photophysical properties provided guidance for further modification of cercosporin, which could be applied to more meaningful and challenging energy-transfer reactions.
- Zhang, Yan,Xia, Mingze,Li, Min,Ping, Qian,Yuan, Zhenbo,Liu, Xuanzhong,Yin, Huimin,Huang, Shuping,Rao, Yijian
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p. 15284 - 15297
(2021/11/01)
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- An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne cis-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
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The selective synthesis of Z-alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report Z-selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl- dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl (1) forms a cationic monohydride, [(NCP)IrH(EtOH)]+Cl-, that reacts selectively with alkynes over the corresponding Z-alkenes, thereby overcoming competing thermodynamically dominant alkene Z-E isomerization and overreduction. The challenge for establishing a catalytic cycle, however, lies in the alcoholysis step; the reaction of the alkyne insertion product (NCP)IrCl(vinyl) with EtOH does occur, but very slowly. Surprisingly, the alcoholysis does not proceed via direct protonolysis of the Ir-C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl- ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)-H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting the alcoholysis. The 1-amine-EtOH catalytic system exhibits an unprecedented level of substrate scope, generality, and compatibility, as demonstrated by Z-selective reduction of all alkyne classes, including challenging enynes and complex polyfunctionalized molecules. Comparison with a cationic monohydride complex bearing a noncoordinating BArF- ion elucidates the beneficial role of the Cl- ion in controlling the stereoselectivity, and comparison between 1-amine-EtOH and 1-NaOtBu-EtOH underscores the fact that this base variable, albeit in catalytic amounts, leads to different mechanisms and consequently different stereoselectivity.
- Huang, Zhidao,Wang, Yulei,Leng, Xuebing,Huang, Zheng
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supporting information
p. 4824 - 4836
(2021/04/07)
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- E, Z -Selectivity in the reductive cross-coupling of two benzaldehydes to stilbenes under substrate control
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Unsymmetrical E- and Z-stilbenes can be synthesized from two differently substituted benzaldehydes in a MesP(TMS)Li-promoted reductive coupling sequence. Depending on the order of addition of the two coupling partners, the same olefin can be produced in either E- or Z-enriched form under identical reaction conditions. A systematic study of the correlation between the stereochemical outcome of the reaction and the substitution pattern at the two aldehydes is presented. The results can be used as guidelines to predict the product stereochemistry. This journal is
- Arkhypchuk, Anna I.,D'Imperio, Nicolas,Ott, Sascha
-
supporting information
p. 6171 - 6179
(2020/10/21)
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- Acetylene as a Dicarbene Equivalent for Gold(I) Catalysis: Total Synthesis of Waitziacuminone in One Step
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The gold(I)-catalyzed reaction of acetylene gas with alkenes leads to (Z,Z)-1,4-disubstituted 1,3-butadienes and biscyclopropanes depending on the donor ligand on gold(I). Acetylene was generated in situ from calcium carbide and water in a user-friendly p
- Armengol-Relats, Helena,Echavarren, Antonio M.,Escofet, Imma,Korber, J. Nepomuk,Scharnagel, Dagmar,de Orbe, M. Elena
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supporting information
p. 4888 - 4891
(2020/02/11)
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- Selenenate Anions (PhSeO?) as Organocatalyst: Synthesis of trans-Stilbenes and a PPV Derivative
-
The selenenate anion (RSeO?) is introduced as an active organocatalyst for the dehydrohalogen coupling of benzyl halides to form trans-stilbenes. It is shown that RSeO? is a more reactive catalyst than the previously reported sulfur analogues (sulfenate anion, RSO?) and selenolate anions (RSe?) in the aforementioned reaction. This catalytic system was also applied to the benzylic-chloromethyl-coupling polymerization (BCCP) of a bis-chloromethyl arene to form ppv (poly(p-phenylene vinylene))-type polymers with high yields, Mn (average molecular weight) up to 13,000 and ? (dispersity) of 1.15. (Figure presented.).
- Zheng, Zhipeng,Trofymchuk, Oleksandra S.,Kurogi, Takashi,Varela, Elena,Mindiola, Daniel J.,Walsh, Patrick J.
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supporting information
p. 659 - 666
(2020/01/02)
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- Using alcohols as simple H2-equivalents for copper-catalysed transfer semihydrogenations of alkynes
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Copper(i)/N-heterocyclic carbene complexes enable a transfer semihydrogenation of alkynes employing simple and readily available alcohols such as isopropanol. The practical overall protocol circumvents the use of commonly employed high pressure equipment when using dihydrogen (H2) on the one hand, and avoids the generation of stoichiometric silicon-based waste on the other hand, when hydrosilanes are used as terminal reductants.
- Kaicharla, Trinadh,Zimmermann, Birte M.,Oestreich, Martin,Teichert, Johannes F.
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supporting information
p. 13410 - 13413
(2019/11/14)
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- Photoinitiated carbonyl-metathesis: Deoxygenative reductive olefination of aromatic aldehydes: Via photoredox catalysis
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Carbonyl-carbonyl olefination, known as McMurry reaction, represents a powerful strategy for the construction of olefins. However, catalytic variants that directly couple two carbonyl groups in a single reaction are less explored. Here, we report a photoredox-catalysis that uses B2pin2 as terminal reductant and oxygen trap allowing for deoxygenative olefination of aromatic aldehydes under mild conditions. This strategy provides access to a diverse range of symmetrical and unsymmetrical alkenes with moderate to high yield (up to 83%) and functional-group tolerance. To follow the reaction pathway, a series of experiments were conducted including radical inhibition, deuterium labelling, fluorescence quenching and cyclic voltammetry. Furthermore, NMR studies and DFT calculations were combined to detect and analyze three active intermediates: a cyclic three-membered anionic species, an α-oxyboryl carbanion and a 1,1-benzyldiboronate ester. Based on these results, we propose a mechanism for the CC bond generation involving a sequential radical borylation, "bora-Brook" rearrangement, B2pin2-mediated deoxygenation and a boron-Wittig process.
- Wang, Shun,Lokesh, Nanjundappa,Hioe, Johnny,Gschwind, Ruth M.,K?nig, Burkhard
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p. 4580 - 4587
(2019/05/14)
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- Selenolate Anion as an Organocatalyst: Reactions and Mechanistic Studies
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A new organocatalyst, the selenolate anion [RSe]–, generated from bench-stable and commercially available diphenyl diselenide or from phenyl benzyl selenide (10 mol%) is introduced. Benchmarking is performed in the conversion of benzylic chlorides into trans-stilbenes selectively at room temperature. Mechanistic studies support the intermediacy of the selenolate anion and of 1,2-diphenylethyl phenyl selenide. (Figure presented.).
- Trofymchuk, Oleksandra S.,Zheng, Zhipeng,Kurogi, Takashi,Mindiola, Daniel J.,Walsh, Patrick J.
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p. 1685 - 1692
(2018/03/21)
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- An alkene-promoted borane-catalyzed highly stereoselective hydrogenation of alkynes to give Z- And E-alkenes
-
The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Zalkenes, the hydrogenation of alkynes to give E-alkenes is still not well resolved. In particular, selective preparation of both Z- and E-alkenes by the same catalytic hydrogenation system using molecular H2 has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C6F5)2-catalyzed metal-free hydrogenation of alkynes was adopted. Significantly, both Z - and E-alkenes can be furnished by hydrogenation with molecular H2 in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H2 play an essential role in promoting the hydrogenolysis reaction.
- Liu, Yongbing,Hu, Lianrui,Chen, Hui,Du, Haifeng
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supporting information
p. 3495 - 3501
(2015/03/04)
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- A new role for sulfenate anions: Organocatalysis
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(Chemical Equation Presented) The sulfenate anion is introduced for the first time as a catalyst and was found to facilitate the conversion of benzyl halides to trans-stilbenes. CPME=Cyclopentyl methyl ether.
- Schwan, Adrian L.
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p. 226 - 227
(2015/03/03)
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- Tert-butyl phenyl sulfoxide: A traceless sulfenate anion precatalyst
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tert-Butyl phenyl sulfoxide is employed as a traceless precatalyst for the generation of sulfenate anions under basic conditions and has been used to catalyze the coupling of benzyl halides to trans-stilbenes. The advantage of this precatalyst over previous precatalysts is that the byproduct generated on catalyst formation is a gas, facilitating product isolation in high purity. Using this second generation catalyst, a variety of trans-stilbenes were generated in 39-98% isolated yield.
- Zhang, Mengnan,Jia, Tiezheng,Sagamanova, Irina K.,Pericás, Miquel A.,Walsh, Patrick J.
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supporting information
p. 1164 - 1167
(2015/03/14)
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- Ethylaluminum as an ethylene source for the Mizoroki-Heck-type reaction. Rhodium-catalyzed preparation of stilbene derivatives
-
Treatment of an organoaluminum reagent bearing aryl and ethyl groups furnishes 1,2-diarylethene derivatives in good to excellent yields by the catalysis of a rhodium complex, in which the ethyl group of the aluminum reagent serves as an ethylene source in the product formation.
- Tanaka, Shota,Itami, Kazuki,Sunahara, Kazuhiro,Tatsuta, Go,Mori, Atsunori
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supporting information
p. 1949 - 1952
(2015/02/05)
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- Synthesis of a guanidine NHC complex and its application in borylation reactions
-
Synthesis of guanidine-linked NHC can be achieved easily through reacting amino-NHC with carbodiimide. Subsequently, guanidine-NHC Ag and Cu complexes were isolated and fully characterized. These Cu complexes are found to be versatile catalysts for hydroboration, semihydrogenation and carboboration of alkynes in a highly stereo- and regioselective fashion.
- Tai, Chia-Cheng,Yu, Ming-Shiuan,Chen, Yi-Lin,Chuang, Wen-Hang,Lin, Ting-Hua,Yap, Glenn P. A.,Ong, Tiow-Gan
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supporting information
p. 4344 - 4346
(2014/04/17)
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- A new class of organocatalysts: Sulfenate anions
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Sulfenate anions are known to act as highly reactive species in the organic arena. Now they premiere as organocatalysts. Proof of concept is offered by the sulfoxide/sulfenate-catalyzed (1-10 mol%) coupling of benzyl halides in the presence of base to generate trans-stilbenes in good to excellent yields (up to 99%). Mechanistic studies support the intermediacy of sulfenate anions, and the deprotonated sulfoxide was determined to be the resting state of the catalyst. Sulfenates take center stage: Sulfenate anions are known as highly reactive species in the organic arena. Now they premiere as organocatalysts: A sulfoxide/sulfenate (1-10 mol%) promotes the transformation of benzyl halides into trans-stilbenes under basic conditions (up to 99% yield). CPME=cyclopentyl methyl ether.
- Zhang, Mengnan,Jia, Tiezheng,Yin, Haolin,Carroll, Patrick J.,Schelter, Eric J.,Walsh, Patrick J.
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supporting information
p. 10755 - 10758
(2015/05/13)
-
- Unequivocal experimental evidence for a unified lithium salt-free wittig reaction mechanism for all phosphonium ylide types: Reactions with β-heteroatom-substituted aldehydes are consistently selective for cis-oxaphosphetane-derived products
-
The true course of the lithium salt-free Wittig reaction has long been a contentious issue in organic chemistry. Herein we report an experimental effect that is common to the Wittig reactions of all of the three major phosphonium ylide classes (non-stabilized, semi-stabilized, and stabilized): there is consistently increased selectivity for cis-oxaphosphetane and its derived products (Z-alkene and erythro-β-hydroxyphosphonium salt) in reactions involving aldehydes bearing heteroatom substituents in the β-position. The effect operates with both benzaldehydes and aliphatic aldehydes and is shown not to operate in the absence of the heteroatom substituent on the aldehyde. The discovery of an effect that is common to reactions of all ylide types strongly argues for the operation of a common mechanism in all Li salt-free Wittig reactions. In addition, the results are shown to be most easily explained by the [2+2] cycloaddition mechanism proposed by Vedejs and co-workers as supplemented by Aggarwal, Harvey, and co-workers, thus providing strong confirmatory evidence in support of that mechanism. Notably, a cooperative effect of ortho-substituents in the case of semi-stabilized ylides is confirmed and is accommodated by the cycloaddition mechanism. The effect is also shown to operate in reactions of triphenylphosphine-derived ylides and has previously been observed for reactions under aqueous conditions, thus for the first time providing evidence that kinetic control is in operation in both of these cases.
- Byrne, Peter A.,Gilheany, Declan G.
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p. 9225 - 9239
(2012/07/14)
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- Sodium sulfinate-mediated trans-stilbene formation from benzylic halides
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A convenient and efficient method for the synthesis of various symmetrical and non-symmetrical trans-stilbene derivatives from benzylic halides in the absence of any transition metals is described. Sodium sulfinates played an important role in this transformation. Various functional groups were well tolerated under the optimized reaction conditions. Copyright
- Zhao, Feng,Luo, Jiaying,Tan, Qi,Liao, Yunfeng,Peng, Shengming,Deng, Guo-Jun
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supporting information; experimental part
p. 1914 - 1918
(2012/09/22)
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- Convenient and stereoselective synthesis of symmetrical (E)-stilbenes via homocoupling of 1,3-dibenzylbenzotriazolium bromides
-
Using NaH as the base and DMSO as the solvent, a series of symmetric (E)-stilbenes were prepared in good yields via the -homocoupling of 1,3-dibenzylbenzotriazolium bromides at room temperature. Georg Thieme Verlag Stuttgart · New York.
- Xiao, Xiaohui,Lin, Daqin,Tong, Shuitian,Luo, Hong,He, Yinfeng,Mo, Hailan
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supporting information; experimental part
p. 1731 - 1734
(2011/09/16)
-
- Selective cine substitution of 1-arylethenyl acetates with arylboron reagents and a diene/rhodium catalyst
-
When the crowd says Bo: A carbon-carbon bond is selectively formed at the β position of 1- arylethenyl acetate when the alkenyl substrate is reacted with arylboronic acids in the presence of a cycloocta-1,5-diene/rhodium catalyst. The choice of the ligand is crucial for the unusual cine substitution. Copyright
- Yu, Jung-Yi,Shimizu, Ryosuke,Kuwano, Ryoichi
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supporting information; experimental part
p. 6396 - 6399
(2010/11/17)
-
- Studies on the 1,2-migrations in Pd-catalyzed negishi couplings with JosiPhos ligands
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(Chemical Equation Presented) We report an initial investigation with the goal of determining the factors that control the 1,2-migration in the Negishi cross-coupling, which is promoted by palladium catalyst systems generated with JosiPhos ligands. Severa
- Lindhardt, Anders T.,G?gsig, Thomas M.,Skrydstrup, Troels
-
supporting information; experimental part
p. 135 - 143
(2009/04/07)
-
- Catalytic enantioselective allyl- and crotylboration of aldehydes using chiral diol·SnCl4 complexes. Optimization, substrate scope and mechanistic investigations
-
We report a novel class of C2-symmetric chiral diols derived from the hydrobenzoin skeleton. The combination of these diols with SnCl 4 under Yamamoto's concept of Lewis acid assisted Bronsted acidity (LBA catalysis) leads to high levels of asymmetric induction in the allylboration of aldehydes by commercially available allylboronic acid pinacol ester 1a. The corresponding homoallylic alcohol products of synthetically useful aliphatic aldehydes are obtained in excellent yields with up to 98:2 er. This combined acid manifold is also efficient in catalyzing the diastereo- and enantioselective crotylboration of aldehydes, thus providing the propionate units in >95:5 dr and up to 98:2 er. The X-ray crystal structure of the optimal diol·SnCl4 complex, Vivol (4m)·SnCl 4, unambiguously shows the Bronsted acidic character of this LBA catalyst and its highly dissymmetrical environment. Further controls have ruled out a possible boron transesterification mechanism with the chiral diol and point to LBA catalyst-derived activation of the pinacol allylic boronates 1. Due to slow dissociation of the diol·SnCl4 complex, a small excess of diol is required in order to suppress a competing racemic cycle catalyzed by free SnCl4.
- Rauniyar, Vivek,Zhai, Huimin,Hall, Dennis G.
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supporting information; experimental part
p. 8481 - 8490
(2009/02/02)
-
- Tandem pinacol coupling-rearrangement of aromatic aldehydes with hydrogen catalyzed by a combination of a platinum complex and a polyoxometalate
-
Together with a strongly oxidizing polyoxometalate, H5PV 2Mo10O40, PtII(N-(2,6- diisopropylphenyl)pyrazin-2-ylmethanimine)Cl2 forms a combined catalyst that was active in the tandem pinacol coupling-rearrangement of aryl aldehydes to give mostly the corresponding diarylacetaldehyde in high yields using molecular hydrogen as the reducing agent. The Royal Society of Chemistry.
- Branytska, Olena,Shimon, Linda J. W.,Neumann, Ronny
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p. 3957 - 3959
(2008/10/09)
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- A very simple synthesis of chloroalkenes and chlorodienes by selective Suzuki couplings of 1,1- and 1,2-dichloroethylene
-
Chloroalkenes, important building blocks for cross-coupling reactions, are prepared in one step by the Suzuki reaction of 1,1-dichloroethylene and 1,2-dichloroethylene with alkenyl- and arylboronic acids. Under the proper reaction conditions, it is possible to obtain the monocoupling reaction to provide the corresponding chloroalkenes with good yields. This method represents an excellent route for the preparation of chloroalkenes and chlorodienes from commercially available starting materials.
- Barluenga, Jose,Moriel, Patricia,Aznar, Fernando,Valdes, Carlos
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p. 347 - 353
(2007/10/03)
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- Reduction of alkynes into 1,2-dideuterioalkenes with hexamethyldisilane and deuterium oxide in the presence of a palladium catalyst
-
A combination of hexamethyldisilane and deuterium oxide was found to work as a deuterium transfer reagent for alkynes in the presence of a catalytic amount of a palladium complex to give (E)-1,2-dideuterioalkenes selectively through the corresponding (Z)-isomer. The Royal Society of Chemistry 2005.
- Shirakawa, Eiji,Otsuka, Hidehito,Hayashi, Tamio
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p. 5885 - 5886
(2007/10/03)
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- Photoisomerization by Hula twist: 2,2′-Dimethylstilbene and a ring-fused analogue
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Let's twist again: While the photoisomerization of stilbene analogues in fluid solution occurs by a one-bond-flip mechanism and involves only configurational changes, in a solid solution (glass) a Hula-twist mechanism operates and results in conformationa
- Imamoto, Yasushi,Kuroda, Takayuki,Kataoka, Mikio,Shevyakov, Sergey,Krishnamoorthy,Liu, Robert S. H.
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p. 3630 - 3633
(2007/10/03)
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- Synthesis of trans-stilbenes utilising decarbonylation of α-chloro chloroformates mediated by samarium diiodide
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A new synthesis of trans-stilbenes has been achieved by decarbonylation of α-chloro chloroformates mediated by samarium diiodide in THF; this one pot reaction is completed within a few minutes at room temperature.
- Li, Zhifang,Zhang, Yongmin
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p. 340 - 341
(2007/10/03)
-
- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
-
Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
-
- Anti-selective glycolate aldol additions with an oxapyrone boron enolate
-
The boron enolate of pyrone 2 undergoes asymmetric aldol reactions with aldehydes to give protected anti 1,2-diols 3. The pyrone is readily available from trans stilbene using asymmetric dihydroxylation. Yields for the aldol reaction range from 62 to 92%
- Andrus, Merritt B.,Sekhar, B. B. V. Soma,Meredith, Erik L.,Dalley, N. Kent
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p. 3035 - 3037
(2007/10/03)
-
- Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 12. Extrusion of Ph3P from sulfonyl ylides and reactivity of the resulting sulfonyl carbenes
-
Twelve sulfonyl stabilised phosphorus ylides have been prepared and their behaviour upon flash vacuum pyrolysis at 600°C has been examined. Examples with an arylsulfonyl substituent undergo loss of Ph3PO to give intractable products but those with an arylmethylsulfonyl substituent separately lose Ph3P and SO2 to give products consistent with the intermediacy of sulfonyl carbenes. X-Ray structure determinations of one ylide from each series show a more significant P-O non-bonding interaction in the first case, providing some explanation for the different thermal reactivity.
- Aitken, R. Alan,Drysdale, Martin J.,Ferguson, George,Lough, Alan J.
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p. 875 - 880
(2007/10/03)
-
- Synthesis of trans-4,4′-diiodostilbene and other symmetrical trans-stilbenes by Heck reaction of arenediazonium salts with vinyltriethoxysilane
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With anilines as the starting materials, a facile new synthesis of symmetrical trans-stilbenes, in particular of trans-4,4′-diiodostilbene, by (double) Heck reaction of arenediazonium salts with vinyltriethoxysilane is described.
- Sengupta, Saumitra,Bhattacharyya, Sanchita,Sadhukhan, Subir Kumar
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p. 275 - 277
(2007/10/03)
-
- Heterodiene cycloadditoins of C2 symmetric 4,5-disubstituted ketene acetals: the nett asymmetric conjugate addition of recyclable acetic ester enolate equivalents to an activated enone
-
Heterodiene cycloadditions of 3-formylchromone 2 to a series of ketene acetals 1 derived from C2 symmetric 1,2-diarylethane-1,2-diols are diastereoselective.From (S,S)-1,2-di(o-tolyl)ethane-1,2-diol 6c the major cycloadduct 3c was isolated by crystallization and transformed by acid-catalysed methanolysis into (S)-methyl 4-oxo-3,4-dihydro-2H-1-benzopyran-2-ylacetate 5, together with the original 1,2-diol 6c which could be recycled.The structures of two cyclic carbonates 22a and 22c were determined by X-ray diffraction and used as models in seeking a mechanistic rationale for the stereoselective cycloadditions of the analogous ketene acetals 1a and 1c.
- Wallace, Timothy W.,Wardell, Ian,Li, Ke-Dong,Leeming, Peter,Redhouse, Alan D.,Challand, S. Richard
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p. 2293 - 2308
(2007/10/02)
-
- Intramolecular Reactivity of Arylcarbenes: Derivatives of o-Tolylcarbene
-
Various CH2X groups have been attached to the ortho position of phenylcarbene.If 2'- or 3'-C-H bonds are present, as in 23 (X = Me), 71 (X = CMe3), and 58 (X = SiMe3), C-H insertion leading to five- or six-membered rings predominates in the gas phase and competes with intermolecular reactions in solution.The formation of benzocyclobutenes via insertion into 1'-C-H bonds is a very minor reaction path of 23 and 71.In contrast, 58 produces substantial amounts of the benzocyclobutene 59 by way of C-Si insertion, particularly in the gas phase.Insertion into the Si-Me bonds of 58 also occurs while the C-F bonds of 37 (X = CF3) and 50 (X = F) are inert.In the gas phase, 37 and 50 give mainly benzocyclobutenes whereas intermolecular reactions prevail in solution.The effects of sensitization and of solvent polarity suggest that benzocyclobutenes arise from singlet arylcarbenes.The amount of carbene-carbene rearrangement decreases in the order 7 (X = H) > 37 (X = CF3) > 23 (X = Me); no rearrangement was observed with 50 (X = F), 58 (X = SiMe3), and 71 (X = CMe3).
- Kirmse, Wolfgang,Konrad, Wolfgang,Schnitzler, Dirk
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p. 3821 - 3829
(2007/10/02)
-
- Ramberg Baecklund type reactions of phosphonium salts
-
Alkenes may be synthesised from (α-bromobenzyl)benzyldiphenylphosphonium salts by the action of amine bases. A series of stilbenes was synthesised by the action of N-bromosuccinimide and 2,2,6,6-tetramethylpiperidine directly upon dibenzyldiphenylphosphonium salts. The reaction, essentially a phosphonium analogue of the Ramberg Baecklund displays a similar level of cis selectivity as that shown by the parent sulfone.
- Lawrence, Nicholas J.,Muhammad, Faiz
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p. 5903 - 5906
(2007/10/02)
-
- Efficient synthesis of benzylphosphine oxides and E-stilbenes
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A series of substituted benzylphosphine oxides has been synthesized by reduction of the corresponding (α-chlorobenzyl)phosphine oxide, derived from the benzaldehyde and chlorodiphenylphosphine, with either sodium borohydride (DMSO, 60-70 °C, 12 h) or tributyltin hydride and AIBN (C6H6, 80 °C, 2 h). Reaction of the (α-lithiobenzyl)phosphine oxide with aldehydes gave exclusively E-alkenes.
- Brown,Brown, Karen M.,Lawrence,Lawrence, Nicholas J.,Liddle,Liddle, John,Muhammad,Muhammad, Faiz,Jackson,Jackson, David A.
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p. 6733 - 6736
(2007/10/02)
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- Formation and Reactivity of ?-Radical Cation Intermediates in the C-C Coupling Reaction of Phenyldiazomethanes by One-Electron Oxidation
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One-electron oxidation of phenyldiazomethanes afforded cis-stilbene predominantly.The reaction was independent of the oxidation methods, e.g., electrolysis, copper(II), triarylaminium salts, or photosensitized one-electron oxidtions.The C-C coupling reaction was retarded by introducing α-substituents on phenyldiazomethanes.The ESR spectra of diazoalkane radical cations could be obtained during the electrolysis at low temperature and the resulting spectra revealed their unique electronic structure as ?-radicals for most cases.When a bulky tert-butyl group was substituted, the corresponding ?-radical cation was observed, but the C-C coupling reaction did not occur.The novel HOMO-LUMO switching by one-electron removal from the HOMO ?-orbital of diazomethane is explained by the interaction of phenyl group with the C-N-N ?-radical moiety.The C-C coupling reaction proceeds via facile cycloaddition between the diazomethane and ?-radical cation, and the preferential formation of cis-olefins is based on the secondary orbital interaction between the two phenyl groups.The structure and the stability of radical cation intermediates are rationalized on the basis of ab initio calculations.
- Ishiguro, Katsuya,Ikeda, Masatoshi,Sawaki, Yasuhiko
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p. 3057 - 3066
(2007/10/02)
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- REDUCTIVE COUPLING OF BENZOIC ACID HALIDES AND ESTERS USING LOW-VALENT TITANIUM
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The reductive coupling of (substituted) benzoic acid chlorides and esters is achieved using low-valent titanium, generated from TiCl3 and LiAlH4.Both acid chlorides and esters seem to follow the same two reaction pathways: one path via tolanes to stilbenes, the other via benzils to complex mixtures of products arising from reduction and further coupling reactions.Although the exact product balance depends upon the reaction conditions the major product is (substituted) cis-stilbene.
- Dang, Y.,Geise, H. J.
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p. 375 - 380
(2007/10/02)
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- A NOVEL SINGLE POT REACTION FOR SUBSTITUTION AND CROSS-COUPLING OF VINYLACETATE TO TRANS-STILBENES BY INTERLAMELLAR MONTMORILLONITE PALLADIUM CATALYST
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Synthesis of trans-stilbenes on substitution and cross-coupling of vinylacetate by interlamellar montmorillonite ethyl silyldiphenylphosphinepalladium(II)chloride catalyst is described.
- Choudary, B. M.,Sarma, M. Ravichandra
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p. 1495 - 1496
(2007/10/02)
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- Ultrasound-Mediated Synthesis and Mass Spectrometric Fragmentation of Dimethyl-Substituted 1,2-Diphenylethanols, Convenient Dimethylstilbene Precursors
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1,2-Diarylethanols were obtained in high yields by ultrasonic irradiation of mixtures of lithium sand, benzylic chlorides, and arenecarbaldehydes or aryl methyl ketones.The mass spectra of the alcohols contained dominant peaks for species formed by dehydration, α-cleavage processes and rearrangement involving hydrogen transfer.Acid-catalyzed dehydration of the alcohols gave the corresponding stilbenes in quantitative yields.
- Burkow, Ivan C.,Sydnes, Leiv K.,Ubeda, Danielle C. N.
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p. 235 - 244
(2007/10/02)
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- ZEOLITE-CuNaY CATALYZED DECOMPOSITION OF ARYLDIAZOMETHANE
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Decomposition of aryldiazomethanes is catalyzed by copper ion-exchanged Y-type zeolite to afford cis-1,2-diarylethylenes in high selectivity.The catalytic activity and selectivity are found to be affected by the exchange level of copper ions in zeolite and the solvent used.
- Onaka, Makoto,Kita, Hiroshi,Izumi, Yusuke
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p. 1895 - 1898
(2007/10/02)
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- sym-1,2-Diarylethylenes from α-Lithiated Benzylic Sulfones. Catalysis by Elemental Tellurium
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The stability of α-lithiated alkyl, allyl, and benzyl phenyl sulfones was studied. α-Lithiated benzyl phenyl sulfones were found to give sym-1,2-diarylethylenes slowly when kept in tetrahydrofuran at ambient temperature for several days.The reaction time was significantly reduced if a catalytic amount (18-24percent) of elemental tellurium was present in the reaction.Other chalcogenides were less effective in this respect.The uncatalyzed reaction produced essentially pure trans olefins whereas the tellurium-catalyzed process afforded substantial amounts of cis isomer(usually 15-35percent).Tellurium tetrachloride in chloroform at ambient to reflux temperature was found to be highly effective in promoting cis/trans isomerization of 1,2-diarylethylenes.The involvement of a carbene mechanism or an intermolecular reaction of α-lithiated benzyl phenyl sulfones is considered in a mechanistic discussion.
- Engman, Lars
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p. 3559 - 3563
(2007/10/02)
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- NEW SIMPLE METHOD FOR THE SYNTHESIS OF CIS-STILBENES
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A new method involving catalytic acetylenic condensation as the key stage was developed for the synthesis of cis-stilbenes.Subsequent selective hydrogenation of the synthesized alkyltolanes over Pd-CaCO3 gave a series of alkyl-substituted stilbenes. 1,8-Dimethylphenanthrene was obtained from o-iodotoluene.
- Merkushev, E. B.,Skorokhodova, T. S.
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p. 308 - 311
(2007/10/02)
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