- Electro-mediated PhotoRedox Catalysis for Selective C(sp3)–O Cleavages of Phosphinated Alcohols to Carbanions
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We report a novel example of electro-mediated photoredox catalysis (e-PRC) in the reductive cleavage of C(sp3)?O bonds of phosphinated alcohols to alkyl carbanions. As well as deoxygenations, olefinations are reported which are E-selective and can be made Z-selective in a tandem reduction/photosensitization process where both steps are photoelectrochemically promoted. Spectroscopy, computation, and catalyst structural variations reveal that our new naphthalene monoimide-type catalyst allows for an intimate dispersive precomplexation of its radical anion form with the phosphinate substrate, facilitating a reactivity-determining C(sp3)?O cleavage. Surprisingly and in contrast to previously reported photoexcited radical anion chemistries, our conditions tolerate aryl chlorides/bromides and do not give rise to Birch-type reductions.
- Barham, Joshua P.,K?nig, Burkhard,Karl, Tobias A.,Reiter, Sebastian,Tian, Xianhai,Yakubov, Shahboz,de Vivie-Riedle, Regina
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supporting information
p. 20817 - 20825
(2021/08/18)
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- A donor-acceptor complex enables the synthesis of: E -olefins from alcohols, amines and carboxylic acids
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Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor-acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.
- Chen, Kun-Quan,Shen, Jie,Wang, Zhi-Xiang,Chen, Xiang-Yu
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p. 6684 - 6690
(2021/05/31)
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- Switchable Synthetic Strategy toward Trisubstituted and Tetrasubstituted Exocyclic Alkenes
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An efficient and facile method for the construction of tri- or tetrasubstituted exocyclic alkenes is achieved via a Cu(I)-catalytic system. This protocol exhibits mild conditions, low-cost catalyst, good functional group tolerance, and good yields. The selectivity toward tri- or tetrasubstituted alkenes can be delicately controlled by adjustment of base and solvent. A preliminary mechanism study manifested that the reaction undergoes a radical process, where B2pin2 plays an indispensable role.
- Zhou, Sen,Yuan, Fangyuan,Guo, Minjie,Wang, Guangwei,Tang, Xiangyang,Zhao, Wentao
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supporting information
p. 6710 - 6714
(2018/11/21)
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- Synthesis of α-Arylated Cycloalkanones from Congested Trisubstituted Spiro-epoxides: Application of the House-Meinwald Rearrangement for Ring Expansion
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A three-step sequence for the synthesis of α-arylated cyclohexanones and the most challenging cycloheptanones is reported. First, an efficient one-pot synthesis of β,β'-disubstituted benzylidene cycloalkanes (styrenes) using the palladium-catalyzed Barluenga reaction from readily available feedstock chemicals is described. Furthermore, an epoxidation followed by the House-Meinwald rearrangement (HMR) of spiro-epoxides is reported to produce a number of α-arylated cycloalkanones upon ring expansion. Reactions catalyzed by bismuth triflate underwent quasi-exclusively ring expansion for all substrates (electronically poor and rich), with yields ranging from 15% to 95%, thus demonstrating the difficulty of achieving ring enlargement for electron-deficient spiro-epoxides. On the other hand, by means of catalysis with aluminum trichloride, the rearrangement of spiro-epoxides proceeded typically in high yields and with remarkable regioselectivity on a broader substrate scope. In this case, a switch of regioselectivity was achieved for spiro-epoxides with electron-withdrawing substituents which enable the method to be successfully extended to some chemospecific arene shifts and the synthesis of aldehydes bearing a α-quaternary carbon. While the HMR has been extensively studied for smaller ring enlargement, we are pleased to report herein that larger cyclohexanones and cycloheptanones can be obtained efficiently from more sterically demanding trisubstituted spiro-epoxides bearing electron-releasing and electron-neutral arene substituents.
- Jeedimalla, Nagalakshmi,Jacquet, Camille,Bahneva, Diana,Youte Tendoung, Jean-Jacques,Roche, Stéphane P.
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p. 12357 - 12373
(2018/09/06)
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- Consecutive visible-light photoredox decarboxylative couplings of adipic acid active esters with alkynyl sulfones leading to cyclic compounds
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Novel and efficient consecutive photoredox decarboxylative couplings of adipic acid active esters (bis(1,3-dioxoisoindolin-2-yl)-substituted hexanedioates) with substituted 1-(2-arylethynylsulfonyl)benzenes have been developed under visible-light photocatalysis. The successive photoredox decarboxylative C-C bond formation at room temperature afforded the corresponding cyclic compounds in good yields with tolerance of some functional groups.
- Li, Jingjing,Tian, Hua,Jiang, Min,Yang, Haijun,Zhao, Yufen,Fu, Hua
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p. 8862 - 8864
(2016/07/22)
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- Aryltriolborates as air- and water-stable bases for wittig olefination
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Tetrabutylammonium aryltriolborates have been synthesized in 37-66% yield by a one-pot procedure from arylboronic acids, 1,1,1-tris(hydroxymethyl)ethane, and aqueous tetrabutylammonium hydroxide. The aryltriolborates can be used as bases in Wittig reactions of aromatic aldehydes with all three types of phosphorus ylides: stabilized and semistabilized ylides can be generated at room temperature, and nonstabilized ylides at 120 °C (bath temperature).
- Huang, Wenhua,Zhao, Shuang-Hong,Xu, Ning
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p. 359 - 366
(2015/02/19)
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- Rh-catalyzed C-C bond cleavage by transfer hydroformylation
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The dehydroformylation of aldehydes to generate olefins occurs during the biosynthesis of various sterols, including cholesterol in humans. Here, we implement a synthetic version that features the transfer of a formyl group and hydride from an aldehyde substrate to a strained olefin acceptor. A Rhodium(Xantphos)(benzoate) catalyst activates aldehyde carbon-hydrogen (C-H) bonds with high chemoselectivity to trigger carbon-carbon (C-C) bond cleavage and generate olefins at low loadings (0.3 to 2 mole percent) and temperatures (22° to 80°C). This mild protocol can be applied to various natural products and was used to achieve a three-step synthesis of (+)-yohimbenone. A study of the mechanism reveals that the benzoate counterion acts as a proton shuttle to enable transfer hydroformylation.
- Murphy, Stephen K.,Park, Jung-Woo,Cruz, Faben A.,Dong, Vy M.
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- Cyclization of gold acetylides: Synthesis of vinyl sulfonates via gold vinylidene complexes
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Differently substituted terminal alkynes that bear sulfonate leaving groups at an appropriate distance were converted in the presence of a propynyl gold(I) precatalyst. After initial formation of a gold acetylide, a cyclization takes place at the β-carbon atom of this species. Mechanistic studies support a mechanism that is related to that of dual gold-catalyzed reactions, but for the new substrates, only one gold atom is needed for substrate activation. After formation of a gold vinylidene complex, which forms a tight contact ion pair with the sulfonate leaving group, recombination of the two parts delivers vinyl sulfonates, which are valuable targets that can serve as precursors for cross-coupling reactions, for example. Gold vinylidene intermediates are generated by the cyclization of gold acetylides that carry a sulfonate leaving group. This result demonstrates for the first time that the formation of these species is not restricted to a dual activation mode. The cyclization products obtained herein contain a vinyl sulfonate moiety, which makes them useful building blocks for cross-coupling reactions.
- Bucher, Janina,Wurm, Thomas,Nalivela, Kumara Swamy,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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supporting information
p. 3854 - 3858
(2014/05/06)
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- Non-cross-linked polystyrene-supported triphenylarsonium halides and their use in the arsa-Wittig reaction
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Non-cross-linked polystyrene-supported (carbomethoxymethyl) triphenylarsonium bromide (1) and benzyltriphenylarsonium iodide (2) were synthesized. They showed similar reactivities compared with the free arsonium salts in the arsa-Wittig reaction. The use of the polymer-supported reagents facilitated product purification and rendered the organoarsenic reagents easily separable and recyclable.
- Lau, Kelvin C.Y.,Chiu, Pauline
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experimental part
p. 8769 - 8774
(2011/12/02)
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- Silver-catalyzed regioselective carbomagnesiation of alkynes with alkyl halides and Grignard reagents
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A silver-catalyzed carbomagnesiation of alkynes with alkyl halides and Grignard reagents afforded alkenyl Grignard reagents regioselectively, where the alkyl group of the alkyl halide, but not that of the Grignard reagent, was introduced into the alkyne.
- Kambe, Nobuaki,Moriwaki, Yuusuke,Fujii, Yuuki,Iwasaki, Takanori,Terao, Jun
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scheme or table
p. 4656 - 4659
(2011/10/18)
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- Titanocene(III) mediated reduction of organic halides under photoirradiation conditions
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Photoirradiation with a xenon lamp promotes the Cp2TiCl mediated reduction of some unsaturated alkyl halides. Photoirradiation of reaction mixtures, with a xenon lamp in the UV-vis domain, facilitates the titanocene(III) mediated reduction of some organic halides. The substrates studied include ω-halo-α,β-unsaturated esters and a 6-iodohexose derivative.
- Hersant, Grégory,Sadok Ferjani, Mounira Bent,Bennett, Sharon M.
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p. 8123 - 8126
(2007/10/03)
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- A facile method for the construction of highly substituted acetonitriles and olefins. Malononitriles as acetonitrile carbanion and alkylidene dianion equivalents
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The use of malononitrile to facilitate the preparation of highly substituted nitriles, via reductive alkylation/addition, and olefins, via a combination of reductive addition and reductive elimination, is described.
- Tsai, Ting-Yueh,Shia, Kak-Shan,Liu, Hsing-Jang
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- Stereoselective synthesis of δ-lactones from 5-oxoalkanals via one-pot sequential acetalization, tishchenko reaction, and lactonization by cooperative catalysis of samarium ion and mercaptan
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By the synergistic catalysis of samarium ion and mercaptan, a series of 5-oxoalkanals was converted to (substituted) δ-lactones in efficient and stereoselective manners. This one-pot procedure comprises a sequence of acetalization, Tishchenko reaction and lactonization. The deliberative use of mercaptan, by comparison with alcohol, is advantageous to facilitate the catalytic cycle. The reaction mechanism and stereochemistry are proposed and supported by some experimental evidence. Such samarium ion/mercaptan cocatalyzed reactions show the feature of remote control, which is applicable to the asymmetric synthesis of optically active δ-lactones. This study also demonstrates the synthesis of two insect pheromones, (2S,5R)-2-methylhexanolide and (R)-hexadecanolide, as examples of a new protocol for asymmetric reduction of long-chain aliphatic ketones.
- Hsu,Fang
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p. 8573 - 8584
(2007/10/03)
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- Cyclizations during the Grignard Reactions of ω-Bromoalkynes
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The Grignard reactions of a number of ω-bromoalkynes have been shown to undergo regioselective cyclizations in certain instances to give the smaller possible carbocycle. These cyclizations are shown to result from two competing processes, whose relative efficiencies depend upon the chain length and the remote substitutent on the acetylene. These are interpreted as a radical cyclization which occurs only during the time the Grignard is being formed from the bromide and an organometallic reaction which slowly transforms the Grignard reagent into its cyclic isomer. The mechanistic details of these transformations are discussed.
- Crandall, Jack K.,Michaely, William J.,Collonges, Francois,Nelson, Deanna J.,Ayers, Timothy A.,Gajewski, Joseph J.
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p. 1473 - 1490
(2007/10/03)
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- Radical reactions in organoboron chemistry II - Inter- and intramolecular addition of carbon centered radicals to alkenylboranes
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The intermolecular addition of carbon centered radicals to alkenylboranes has been studied. The influence of the olefin and boron substituents on the reactivity and the regioselectivity was determined. Competitive experiments were carried out to estimate the relative reactivity of a series of vinylboranes and other electron deficient alkenes. Intramolecular versions of these additions were also described as well as some further transformations of selected adducts.
- Guennouni,Lhermitte,Cochard,Carboni
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p. 6999 - 7018
(2007/10/02)
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- Reactions of some alkynyl halides with samarium(II) iodide
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Certain alkynyl halides (6-halo-1-ynes) react with samarium(II) iodide (SmI2) to give cyclized products (methylenecyclopentanes) in good yield. We have found some interesting evidence for the presence of radical and unstable organosamarium intermediates in these reductive cyclizations. Methyl 7-halohept-2-ynoates are not, however, good substrates for this cyclization methodology.
- Zhou, Zhihong,Larouche, Denis,Bennett, Sharon M.
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p. 11623 - 11644
(2007/10/02)
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- Stereochemistry of direct olefin formation from carbonyl compounds and lithiated heterocyclic sulfones
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The conditions for the title reaction were studied for the 2-benzothiazole and 2-pyridine series and for some examples in the 2-pyrimidine series.The olefin preparations were generally observed to be more efficient for 2-BT-sulfone systems.From the data of the hundred cases studied, it can be concluded that (E)-olefins are obtained: (i) from saturated BT-sulfones and aromatic aldehydes; and (ii) from benzylic BT-sulfones and branched saturated aldehydes (isobutyraldehyde, pivalaldehyde) or α,β-ethylenic or aromatic aldehydes. (Z)-olefins arise: (i) fom propargylic BT-sulfones and saturated or aromatic aldehydes; and (ii) from allylic or benzylic Pyr-sulfones and saturated aldehydes.Possible mechanisms for this new olefination procedure were examined. - heteroaromatic sulfones, organolithium derivatives, intramolecular ipso reactions, stereochemistry, elimination, olefination.
- Baudin, J. B.,Hareau, G.,Julia, S. A.,Lorne, R.,Ruel, O.
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p. 856 - 878
(2007/10/02)
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- EFFICIENT OLEFINATION WITH α-ALKYL CYCLIC PHOSPHONAMIDES
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A variety of acyclic and cyclic aldehydes and ketones can be converted into the corresponding alkylidene, benzylidene and methoxycarbonyl alkylidene derivatives by treatment with 1,3,2-diazaphospholidine-2-alkyl-1,3-dimethyl 2-oxides (α-alkyl cyclic phosphonamides) under mild conditions.This olefination method is particularly useful in the case of enolizable carbonyl compounds.
- Hanessian, Stephen,Bennani, Youssef L.,Leblanc, Yves
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p. 1411 - 1424
(2007/10/02)
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- Electrochemical Reduction and Intramolecular Cyclization of 6-Iodo-1-phenyl-1-hexyne at Vitreous Carbon Cathodes in Dimethylformamide
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In dimethylformamide containing a tetraalkylammonium perchlorate, a cyclic voltammogram for reduction of 6-iodo-1-phenyl-1-hexyne at a glassy carbon electrode exhibits three prominent waves corresponding to cleavage of the carbon-iodine bond and to subsequent reductions of 1-phenyl-1-hexyne and benzylidenecyclopentane.At potentials for which only reduction of the carbn-iodine bond occurs, large-scale electrolytes of 6-iodo-1-phenyl-1-hexyne afford benzylidenecyclopentanone and 1-phenyl-1-hexyne; the yield of the carbocycle, averaging 36percent, is insensitive to potential, but the quantity of 1-phenyl-1-hexyne varies from 28 to 48percent as the potential is chosen to be more negative.In the presence of diethyl malonate as a proton donor, the quantity of benzylidenecyclopentane changes little, the yield of 1-phenyl-1-hexyne decreases, and substantial (>33percent) diethyl (1-phenyl-1-hexyn-6-yl)malonate is obtained.With 1,1,1,3,3,3-hexafluoroisopropyl alcohol as proton source, the yield of benzylidenecyclopentane increases to approximately 60percent, whereas the quantity of 1-phenyl-1-hexyne decreases somewhat.It appears that each of the major hydrocarbon products is formed via a combination of one- and two-electron processes.
- Mubarak, Mohammad S.,Nguyen, Dung D.,Peters, Dennis G.
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p. 2648 - 2652
(2007/10/02)
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- The Reactivity of the Highly Functionalized Copper, Zinc Reagents RCu(CN)ZnI Toward 1-Haloalkynes and Acetylenic Esters
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The highly functionalized organometallics RCu(CN)ZnI 1 react efficiently with 1-haloalkynes providing polyfunctionalized alkynes in high yields.This method has been used to prepare a pheromone of the Amathes c-nigrum in 3 steps and 64percent overall yield.The reagents 1 also add in the presence of an excess of Me3SiCl to acetylenic esters to afford polyfunctionalized C-silylated ethylenic esters.In the case of ethyl propiolate, the reaction is highly stereoselective and affords 97percent pure (E)-2-trimethylsilyl ethylenic esters.
- Yeh, Ming Chang P.,Knochel, Paul
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p. 4799 - 4802
(2007/10/02)
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- OLIGOMETHYLENATION OF PHENYLALLENE WITH DIAZOMETHANE IN THE PRESENCE OF PALLADIUM DIACETATE
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In the reaction of phenylallene with diazomethane in the presence of palladium(II) acetate oligomethylenation takes place in addition to cyclopropanation.It leads to the inclusion of three and four equivalences of methylene in the allene molecule.
- Lukin, K. A.,Zefirov, N. S.
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- OLEFIN SYNTHESIS VIA THE LITHIUM DERIVATIVE OF THE N,N,N',N'-TETRAMETHYLDIAMIDES OF ARYLMETHANEPHOSPHONIC ACIDS. 3. SYNTHESYS OF SOME β-DISUBSTITUTED STYRENES
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The reaction of Li-derivatives of N,N,N',N'-tetramethyldiamides of arylmethanephosphonic acids (1-Li) with alkanones, cycloalkanones, alkylaryl- and diarylketones 2a-h is studied.It is found that in THF at -70 deg C adducts 3-Li and 4-Li are formed, the corresponding hydroxyl compounds 3 and 4 being isolated in 36-81percent yields, while by elevated temperatures the reaction is completely shifted to the starting 1-Li and 2.By thermolysis of 3 and 4 in neutral medium olefins 5 and 6 are obtained even from readily enolysable ketones.The stereochemistry of the addition reaction with nonsymmetrical ketones as well as the influence of the substituents at the carbonyl groups on the conformation and adsorption properties of the adducts are discussed.
- Momchilova, Snejana,Petrova, Jordanka,Kirilov, Marko
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p. 319 - 328
(2007/10/02)
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- Tungsten Wittig Reagents: an Efficient Synthesis of α-Functionalised Tri- and Tetra-substituted Alkenes
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The reaction of tungsten alkylidene complexes of the type W(=CR1R2)X2Y2 with organic carbonyl groups is shown to enable a variety of di-, tri-, and tetra-substituted alkenes to be synthesised directly, including enol ethers and enamines.
- Aguero, A.,Kress, J.,Osborn, J. A.
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p. 531 - 533
(2007/10/02)
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- Cyclizations of ω-Alkynyl Halides by Cr(II) Reduction
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Reduction of halides of the types RCC(CH2)nX with Cr(II) in aqueous DMF containing ethylenediamine proceeds by way of the intermediate radicals which cyclize regioselectively in the n=4 and n=5 cases to give substituted methylenecycloalkanes.Experimental conditions which favor longer lifetimes for the intermediate radicals (low concentrations, slow addition times, and an inverse-addition mode) result in increased cyclization.The iodides curiously give more cyclic product than the corresponding bromides.These results are discussed.
- Crandall, Jack. K.,Michaely, W. J.
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p. 4244 - 4248
(2007/10/02)
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- Synthesis and Addition Reactions of 2-Phenyl-1-cyclopropene-1-carboxylates
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From the olefins 1, 2, and 4 - 7 the 1-chloro-1-cyclopropanecarboxylic acids 15 - 20 are prepareded via the dichlorocyclopropanes 8, 9, and 11 - 14.The trans-isomers 15a - 20a were readily separated.Spiropentane 10 undergoes anionic ring cleavage with BuLi to give finally the ester 33.The tert-butyl esters 21 - 26 yield with KOtBu the cyclopropene esters 27 - 32.The trans-esters 21a - 26a react much faster than the cis-esters b.At C-3 unsubstituted chlorocyclopropane esters, e.g. 34, do not give stable cyclopropene esters even with lithium dialkylamides.Diazomethane adds to the esters 27 - 32 to give the pyrazolines 38 - 43, their isomers a and b being separable.With traces of base the bicyclic pyrazolines are cleaved to 1,4-dihydropyridazines 44 - 46.Cyclopropenes 27 - 30 react with thiophenolate to form the isomeric products 47 - 50; malonate adds to 28 and 31 to give 51, 52.With malononitrile via subsequent reactions the cyclopentadienes 55 - 57 are obtained.
- Norden, Wolfgang,Sander, Volker,Weyerstahl, Peter
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p. 3097 - 3111
(2007/10/02)
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