- CATALYZED HYDROSILYLATION OF 2-METHYL-1-BUTEN-3-YNE WITH METHYLDICHLOROSILANE; PROMOTIONAL EFFECT IMPARTED BY THE PRESENCE OF A DIFFERENT CHLOROSILANE
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Chloroplatinic acid catalyzed hydrosilylation of 2-Methyl-1-buten-3-yne with chlorosilanes is reinvestigated; the results can't be satisfactorily explained by Chalk and Harrod mechanism.
- Licchelli, Maurizio,Greco, Alberto
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Read Online
- A mild method for the replacement of a hydroxyl group by halogen: 3. the dichotomous behavior of α-haloenamines towards allylic and propargylic alcohols
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A study of the deoxyhalogenation of allylic and propargylic alcohols with tetramethyl-α-halo-enamines is reported. Primary allylic and primary and secondary propargylic alcohols gave the corresponding halides in high yields. Secondary allylic and propargylic alcohols yielded the corresponding secondary halides but the reaction also produced some rearranged primary halides (I > Br > Cl). The reactions with tertiary allylic and tertiary propargylic alcohols gave several products and was therefore of little synthetic value. However, the addition of triethylamine to the reaction mixture or the use of lithium alkoxide instead of alcohol brought about a major change of the course of the reaction which led to amides carrying an allyl or an allenyl group at C2. This was shown to result from a Claisen-Eschenmoser rearrangement of an intermediate α-allyloxy- or propargyloxy-enamine.
- Munyemana, Fran?ois,Patiny, Luc,Ghosez, Léon
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- Total Synthesis and Biological Investigation of (?)-Artemisinin: The Antimalarial Activity of Artemisinin Is not Stereospecific
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Here, we describe an efficient and diversity-oriented entry to both (?)-artemisinin (1) and its natural antipode (+)-artemisinin, starting from commercially and readily available S-(+)- and R-(?)-citronellene, respectively. Subsequently, we answered the still open question regarding the specificity of artemisinins action. By using a drug-sensitive Plasmodium falciparum NF54 strain, we showed that the antimalarial activity of artemisinin is not stereospecific. Our straightforward and biomimetic approach to this natural endoperoxide enables the synthesis of artemisinin derivatives that are not accessible through applying current methods and may help to address the problem of emerging resistance of Plasmodium falciparum towards artemisinin.
- Krieger, Johannes,Smeilus, Toni,Kaiser, Marcel,Seo, Ean-Jeong,Efferth, Thomas,Giannis, Athanassios
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supporting information
p. 8293 - 8296
(2018/06/29)
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- A new tactic for tocopherol synthesis using intramolecular benzyne trapping by an alcohol
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A formal total synthesis of (S)-α-Tocopherol, the major component of natural Vitamin E has been achieved using intramolecular benzyne trapping as a key step to form the chroman ring. The synthesis also features an efficient new method for benzotriazole N-Amination using an oxaziridine; chiral, nonracemic intermediates are generated using asymmetric dihydroxylation.
- Knight, David W.,Xu, Qing
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p. 647 - 672
(2017/04/10)
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- Aluminum oxide-induced gas-phase ring-opening in methyl substituted gem-difluorocyclopropanes, leading to 2-fluorobuta-1,3-dienes and vinylacetylenes
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A gas-phase pyrolysis of methyl-substituted gem-difluorocyclopropanes in a flow-tube reactor in the presence of Al2O3 at 185 - 250 °C gives 2-fluorobuta-1,3-dienes and vinylacetylenes.
- Volchkov,Lipkind,Novikov,Nefedov
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p. 658 - 663
(2015/11/27)
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- Reaction rate and isomer-specific product branching ratios of C 2H + C4H8: 1-butene, cis -2-butene, trans -2-butene, and isobutene at 79 K
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The reactions of C2H radicals with C4H8 isomers 1-butene, cis-2-butene, trans-2-butene, and isobutene are studied by laser photolysis-vacuum ultraviolet mass spectrometry in a Laval nozzle expansion at 79 K. Bimolecular-reaction rate constants are obtained by measuring the formation rate of the reaction product species as a function of the reactant density under pseudo-first-order conditions. The rate constants are (1.9 ± 0.5) × 10-10, (1.7 ± 0.5) × 10 -10, (2.1 ± 0.7) × 10-10, and (1.8 ± 0.9) × 10-10 cm3 s-1 for the reaction of C2H with 1-butene, cis-2-butene, trans-2-butene, and isobutene, respectively. Bimolecular rate constants for 1-butene and isobutene compare well to values measured previously at 103 K using C2H chemiluminescence. Photoionization spectra of the reaction products are measured and fitted to ionization spectra of the contributing isomers. In conjunction with absolute-ionization cross sections, these fits provide isomer-resolved product branching fractions. The reaction between C2H and 1-butene yields (65 ± 10)% C4H4 in the form of vinylacetylene and (35 ± 10)% C5H6 in the form of 4-penten-1-yne. The cis-2-butene and trans-2-butene reactions yield solely 3-penten-1-yne, and no discrimination is made between cis- and trans-3-penten-1-yne. Last, the isobutene reaction yields (26 ± 15)% 3-penten-1-yne, (35 ± 15)% 2-methyl-1-buten-3-yne, and (39 ± 15)% 4-methyl-3-penten-1-yne. The branching fractions reported for the C2H and butene reactions indicate that these reactions preferentially proceed via CH3 or C2H3 elimination rather than H-atom elimination. Within the experimental uncertainties, no evidence is found for the formation of cyclic species.
- Bouwman, Jordy,Fournier, Martin,Sims, Ian R.,Leone, Stephen R.,Wilson, Kevin R.
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p. 5093 - 5105
(2013/07/25)
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- Bimolecular rate constant and product branching ratio measurements for the reaction of C2H with ethene and propene at 79 K
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The reactions of the ethynyl radical (C2H) with ethene (C 2H4) and propene (C3H6) are studied under low temperature conditions (79 K) in a pulsed Laval nozzle apparatus. Ethynyl radicals are formed by 193 nm photolysis of acetylene (C 2H2) and the reactions are studied in nitrogen as a carrier gas. Reaction products are sampled and subsequently photoionized by the tunable vacuum ultraviolet radiation of the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. The product ions are detected mass selectively and time-resolved by a quadrupole mass spectrometer. Bimolecular rate coefficients are determined under pseudo-first-order conditions, yielding values in good agreement with previous measurements. Photoionization spectra are measured by scanning the ALS photon energy while detecting the ionized reaction products. Analysis of the photoionization spectra yields-for the first time-low temperature isomer resolved product branching ratios. The reaction between C2H and ethene is found to proceed by H-loss and yields 100% vinylacetylene. The reaction between C2H and propene results in (85 ± 10)% C4H4 (m/z = 52) via CH3-loss and (15 ± 10)% C5H6 (m/z = 66) by H-loss. The C 4H4 channel is found to consist of 100% vinylacetylene. For the C5H6 channel, analysis of the photoionization spectrum reveals that (62 ± 16)% is in the form of 4-penten-1-yne, (27 ± 8)% is in the form of cis-and trans-3-penten-1-yne and (11 ± 10)% is in the form of 2-methyl-1-buten-3-yne.
- Bouwman, Jordy,Goulay, Fabien,Leone, Stephen R.,Wilson, Kevin R.
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experimental part
p. 3907 - 3917
(2012/07/02)
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- A synthesis of α-tocopherol featuring benzyne trapping by an alcohol
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A formal total synthesis of α-tocopherol, the main component of Vitamin E, has been achieved in which a central step is the intramolecular trapping of a highly substituted benzyne by an alcohol group to establish the pyran ring.
- Knight, David W.,Qing, Xu
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scheme or table
p. 3534 - 3537
(2009/12/01)
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- Selective oxidation of light alkanes on transition metal promoted vanadyl pyrophosphate (VPO) catalysts
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Vanadyl diphosphate (= vanadyl pyrophosphate) promoted with Bi, Cs, Co and Te was studied as catalyst in the oxidation of propane, n-butane and n-pentane. The additives modified the surface P/V ratio as determined by XPS, and Brinsted and Lewis acidity, determined by TPD of ammonia and transformation of 2-methyl-3-butyn-2-ol. The specific rate of the oxidation of hydrocarbons correlated with the nucleophilicity of surface oxygen ions. With increase of Lewis acidity the selectivity to maleic anhydride in oxidation of n-butane increased, whereas in oxidation of n-pentane the selectivity to phthalic anhydride increased and that to maleic anhydride decreased. The mechanism is discussed.
- Haber,Stoch,Zazhigalov,Bacherikova,Cheburakova
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p. 1839 - 1852
(2008/12/23)
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- Synthesis and characterization of solid acid in system SnO 2/B2O3
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SnO2/B2O3 materials with Sn/B molar ratio 1:1; 1:2 and 1:3 were synthesized from SnCl4, H3BO 3 and (NH2)2CO. The samples contain SnO 2 with different cristallinity and an amorphous borate phase. Their thermal transformations were investigated by DTA method. The surface acidity was investigated by TPR method using conversion of 2-methyl-3-butyn-2-ol (MBOH). The temperature maximum of MBOH dehydration for SnO2/B 2O3 materials is close to that for ZrO2/ SiO2 catalyst. On the surface of SnO2/B2O 3 mainly strong acid sites were detected. In the case of B 2O3/SiO2 (aerosil), samples have mainly weak acid sites. The surface of pure SnO2 has amphoteric sites. IR spectroscopy and MAS NMR spectra of 11B showed that SnO 2/B2O3 materials had three-and four-coordinated B atoms.
- Viter,Nagorny
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experimental part
p. 2081 - 2087
(2009/04/11)
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- Isomerization of propargylic alcohols into α,β-unsaturated carbonyl compounds catalyzed by the sixteen-electron allyl-ruthenium(II) complex [Ru(η3-2-C3H4Me)(CO)(dppf)] [SbF 6]
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The 16-e- (η3-allyl)-ruthenium(II) complex [Ru(η3-2-C3H4Me)(CO)(dppf)][SbF 6] is an efficient catalyst for the regioselective isomerization of terminal propargylic alcohols HC≡CCR1R2(OH) into α,β-unsaturated aldehydes R1R2C=CHCHO or ketones R3R4C=C(R1)COMe (if R2 = CHR3R4) under mild conditions. This complex has been also used as catalyst for the preparation of conjugated 1,3-enynes via dehydration of propargylic alcohols.
- Cadierno, Victorio,Garcia-Garrido, Sergio E.,Gimeno, Jose
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p. 101 - 110
(2007/10/03)
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- Nanoporous metal-containing nickel phosphates: A class of shape-selective catalyst
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A substitute for zeolites: The nanoporous nickel phosphate VSB-1 exhibits zeolitic properties and very weak acidity and basicity (see picture). When VSB-1 is modified by metal-ion exchange or through metal incorporation into the framework, it offers promising catalytic properties, such as shape selectivity, and activity in both redox catalysis and photocatalysis.
- Chang, Jong-San,Hwang, Jin-Soo,Jhung, Sung Hwa,Park, Sang-Eon,Ferey, Gerard,Cheetham, Anthony K.
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p. 2819 - 2822
(2007/10/03)
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- Aldol condensation reactions of acetone and formaldehyde over vanadium phosphate catalysts: Comments on the acid-base properties
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The self-aldol condensation of acetone and the condensation of acetone with formaldehyde over vanadium phosphate catalysts was studied. Catalysts containing only acid sites, i.e., the V4+ phases (VO)2P2O7 and VOHPO4·0.5H2O were selective for the formation of isophorone from acetone alone and methyl vinyl ketone from the reaction of acetone and formaldehyde. Catalysts containing V5+ phases showed basic and acidic sites and were not selective to these products and only formed hydrocarbons. However, for the Aldol condensation of acetone and the decomposition of 2-methyl-3-butynol (MBOH), the catalyst activity was short lived and deactivation was observed due to coke formation on the catalyst surface. For the reaction of MBOH, the data gave a linear relationship for a Cremer-Constable plot due to the high heat of adsorption of MBOH dominating the energies of the overall catalyzed reaction.
- Hutchings,Kelly,Tanner,David Jackson,Gill,Wells,Bailie
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p. 688 - 695
(2007/10/03)
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- Characterization of CrAPO-5 materials in test reactions of conversion of 2-methyl-3-butyn-2-ol and isopropanol
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CrAPO-5 materials with various amounts of Cr(III) stably incorporated into the framework positions were tested in the reactions of conversion of 2-methyl-3-butyn-2-ol (MBOH) and isopropanol. The results were compared with those obtained over similar materials containing extraframework chromium species and over nonsubstituted AlPO4-5. The products of the reactions indicated an increased acidity of catalytic sites in CrAPO-5 compared to that in AlPO4-5. The yield of conversion depends mainly on the amount of chromium and its distribution. The multivalent extraframework Cr species yielded similar catalytic effects as framework Cr centers. However, their activity dropped very quickly due both to the hindrances to alcohol molecules in accessing the catalytic sites in the pores clogged by these species and to the faster coking.
- Zadrozna, Gabriela,Souvage, Emmanuelle,Kornatowski, Jan
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p. 270 - 275
(2007/10/03)
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- Nickel(II) phosphate VSB-5: A magnetic nanoporous hydrogenation catalyst with 24-ring tunnels
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Nanoporosity, good thermal stability, antiferromagnetic ordering, and hydrogenation with basic catalytic character are four important properties of the large-pore (24MR), zeolitic nickel(II) phosphate, VSB-5 (Ni20[(OH)12(H2O)6][(HPO 4)8- (PO4)4]·12H2O), which has been prepared under alkaline hydrothermal conditions. The structure of VSB-5 is depicted: NiO6 octahedra: green; PO4 tetrahedra: red.
- Guillou, Nathalie,Gao, Qiuming,Forster, Paul M.,Chang, Jong-San,Nogueands, Marc,Park, Sang-Eon,Feandrey, Geandrard,Cheetham, Anthony K.
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p. 2831 - 2834
(2007/10/03)
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- Silaheterocyclen XXXVII. Die Kombination Alkeninylhalogensilan/Lithium-tert-Butyl als Synthesebaustein zum Aufbau von Silaheterocyclen mit kumulierten CC-Doppelbindungen
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A series of differently substituted alkeneinylhalogensilanes R2Si(X)-C≡C-C(Me)=CH2 (X = Cl: R = Me (2), Cl (3), Ph (4); X = F: R = Me (5), Mes (6), Tip (7)) is reacted with t-BuLi in solvents of different polarity to give mainly E/Z-isomeric 2,4-bispentenylidene-1,3-disilacyclobutanes (11, 23 and 31) and E/Z-isomeric 2,4,6-trispentenylidene-1,3,5-trisilacyclohexanes (12 and 24) competitively. Obviously the four- and six-membered silacycles are formed stepwise by intermolecular coupling reactions of the lithiated precursors R2Si(X)C(Li)=C=C(Me)-t-Bu which preliminary result from the 1,4-addition of the lithium organyle to the alkeneinylhalogensilanes. Alternatively, silacumulene formation (R2Si=C=C=C(Me)CH2-t-Bu) might be discussed, but the isolation of Cl3Si-C(=C=C(Me)CH2-t-Bu)-C≡C-C(Me)=CH2 (22) as coupling product starting from trichlorosilane 3 and t-BuLi and high molecular multistep coupling products starting from the fluorinated precursors 5 and 7 strongly favour the the coupling reactions over silacumulene formation. Consequently, all attempts to isolate a stable silacumulene from the silicon sterically overcrowded starting compounds 6 and 7 failed.
- Auner, Norbert,Grasmann, Martin
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- Silacyclobutene compounds, methods of preparing same, and polymers formed therefrom
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A silacyclobutene compound having the formula: wherein R1 and R2 are independently chloro, triorganosiloxy, organooxy, triorganosilyl, or a monovalent hydrocarbon group; R3 is a monovalent hydrocarbon group free of conjugated aliphatic unsaturation or triorganosilyl; R5 is hydrogen or a monovalent hydrocarbon group free of conjugated aliphatic unsaturation; and R4 and R6 are independently hydrogen or a monovalent hydrocarbon group free of conjugated aliphatic unsaturation or together are an alkanediyl group, wherein the alkanediyl group and the carbon atoms to which it is attached form a carbocyclic ring having 4 to 7 carbon atoms; provided that R3 is not aryl. Methods of preparing the silacyclobutene compounds, silane polymers containing at least one silacyclobutene unit, and siloxane polymers containing at least one silacyclobutene unit.
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- Structure, texture, acidity and catalytic performance of AlPO4-caesium oxide catalysts in 2-methyl-3-butyn-2-ol conversion
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A series of aluminium orthophosphate-caesium oxide systems with various caesium oxide loadings (5-30 wt%) were prepared by impregnation of ALPO4 with a methanolic solution of caesium acetate and characterized by TG/DTA, XRD, DRIFT, Raman, SEM-EDX, XPS, 27Al and 31P MAS NMR and nitrogen adsorption. Aluminium orthophosphate remained amorphous with caesium oxide incorporation when calcined at 873 K for 3 h. After thermal treatment at 1423 K it crystallized in the tridymite form except for materials containing 30 wt% caesium oxide. DRIFT spectroscopy showed that the P-OH stretching vibration at 3670 cm-1 decreased in intensity with caesium oxide loading. Materials at 20-30 wt% caesium oxide did not exhibit any hydroxyl bands. Besides, Al and P atoms remained in tetrahedral coordination as in unmodified aluminium orthophosphate. Moreover, the incorporation of caesium oxide leads, simultaneously, to a progressive decrease in surface area and pore volume (larger at 30 wt% caesium oxide) as well as to an increase in the most frequently occurring pore radius. On the other hand, caesium oxide reduced both the number and strength of acid sites as the caesium content increased. Consequently, 2-methylbut-3-yn-2-ol (MBOH) underwent almost exclusively dehydration to 3-methyl-3-buten-1-yne (acid activity) on pure AlPO4, whereas its modification with increasing amounts of caesium oxide developed AlPO4- based materials with increased basic properties and hence high selectivities (99 mol%) to the base-catalysed cleavage of MBOH yielding acetone and acetylene.
- Bautista, Felipa M.,Campelo, Juan M.,Garcia, Angel,Leon, Raquel M.,Luna, Diego,Marinas, Jose M.,Romero, Antonio A.,Navio, Jose A.,Macias, Manuel
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p. 827 - 835
(2007/10/03)
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- Porous clay heterostructures (PCH) as acid catalysts
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Porous clay heterostructures formed by surfactant assembly of open framework silica in the galleries of a smectite clay represent a new family of solid acid catalysts, as evidenced by the selective dehydration of 2-methylbut-3-yn-2-ol to 2-methylbut-3-yn-1-ene.
- Galarneau, Anne,Barodawalla, Anis,Pinnavaia, Thomas J.
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p. 1661 - 1662
(2007/10/03)
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- Improved Synthesis of Aryl 1,1-Dimethylpropargyl Ethers
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An efficient, general, and practical synthesis of aryl 1,1-dimethylpropargyl ethers has been developed.
- Godfrey, Jollie D.,Mueller, Richard H.,Sedergran, Thomas C.,Soundarajan, Nachimuthu,Colandrea, Vincent J.
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p. 6405 - 6408
(2007/10/02)
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- The Synthesis of Natural Acetylenic Compounds from Eutypa lata (Pers:F.) TUL.
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The synthesis of a series of novel acetylenic compounds 1-7, isolated recently from the fungus Eutypa lata, is described.The crucial step is the coupling reaction between protected aryl halogenide and the acetylenic chain as a cuprous acetylide (Scheme I).A more efficient method using bis(triphenylphosphine)palladium dichloride () as catalyst was also carried out with success.
- Defranq, Eric,Zesiger, Thierry,Tabacchi, Raffaele
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p. 425 - 430
(2007/10/02)
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- LA PHOTOCHIMIE DE L'ISOPRENE GAZEUX DANS LA REGION DE L'ULTRAVIOLET TRES LOINTAIN
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Yields of various products have been measured in the photolysis of isopropene at 184.9, 213.8, and 228.8 nm and at pressures between 1 and 400 Torr.At each wavelength, the major process is the rupture of a C-CH3 bond, which leads to the formation of methyl and CH2=C=CHCH2.The quantum yield for this process is 0.83 +/- 0.08 at 213.8 nm.The lifetime of the intermediate involved in this process is 20 ns at 184.9 nm.Similar quantities of ethylene and C3H4 (φ >/= 0.050) and propene and acetylene (φ >/= 0.023) are measured.All the measured yields decrease with an increase in the pressure.In addition to these fragmentation processes, isomerization reactions are also observed, particularly at 228.8 nm.They lead to the formation of 1,3- and 1,4-pentadiene as well as 3-methyl-1,2-butadiene.The Stern-Volmer plot for each isomer different and each plot shows a strong negative curvature, indicating the coplexity of the reaction process.The lifetime of each intermediate is 2 ns or less.
- Deslauriers, Helene,Dufour, Sylvain,Collin, Guy J.
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p. 1513 - 1519
(2007/10/02)
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- The Preparation and Lithiation of 1-Halogenocyclopropenes
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Reaction of a range of 1,1,2-trihalogenocyclopropanes (halogen = bromine, chlorine) with methyl-lithium in ether at -90 - 20 deg C leads to 1,2-dehalogenation to the corresponding 1-halogenocyclopropene.The halogenocyclopropenes are readily lithiated by lithium-halogen exchange with a second equivalent of methyl-lithium to give 1-lithiocyclopropenes, which are in turn trapped by electrophiles; an exception to this is compound (21; X = Cl), which leads to 3-methylbuta-1,2-dienylidene (31) by initial lithium-hydrogen exchange and loss of lithium chloride.The cyclopropenes (5; R = Me, X = Br or Cl) and (21; X = Br or Cl) decompose even at temperatures around ambient, leading either to enynes (6; R = Me) or halogenoalkynes (18; X = Br or Cl).A 12C-labelling study indicates that C-1 of the cyclopropene (21; X = Cl) becomes C-2 of the alkyne (18; X = Cl) on rearrangement.
- Baird, Mark S.,Hussain, Helmi H.,Nethercott, William
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p. 1845 - 1854
(2007/10/02)
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- The gasphase photolysis of 2-methy-1,3-butadiene at 123.6 nm
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The gas-phase photolysis of 2-methyl-1,3-butadiene has been investigated using krypton (123.6 nm) resonance radiation.The observed neutral products of the primary decomposition were vinylacetilene, ethylene, acetylene, methylacetylene, propylene, allene, 2-methy-1-buten-3-yne, pentatriene/1-penten-3-yne, 1,3-butadiene, 2-butyne and butatriene, listed in decreasing order of concentration.There was also evidence of the presence of several radical fragments: CH2/CH3, C2H3, C3H3, and C4H5.Quantum yields for each of the products were determined in the photolysis of 2-methyl-1,3-butadiene, performed both in the presence and the absence of additives.Nitric oxide and oxygen were employed as radical scavengers, while hydrogen sulfide and hydrogen iodide were used as radical interceptors.Twelve primary, neutral molecule, reaction channels were proposed and the quantum efficiency assigned for each.The ionization efficiency of 2-methyl-1,3-butadiene was established as n = 0.55 at 10.03 eV.No products formed exclusively via an ion-molecule pathway were identified and therefore the fate of the C5H8+ ion was determined.
- Lang, Valerie I.,Doepker, Richard D.
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p. 1731 - 1735
(2007/10/02)
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- Reactions of 3-Chloro-3-methyl-1-butyne with Hydrogen Chloride: Evidence Against an Electrophilic Addition Reaction
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Reactions of 3-chloro-3-methyl-1-butyne (1) with an excess of anhydrous hydrogen chloride in the liquid phase afforded approx. 16 products.Major product was 1,1,3-trichloro-3-methylbutane (6).In addition, (E)-1,3-dichloro-3-methyl-1-butene (5) and (Z)- and (E)-1,3-dichloro-2-methyl-2-butene (11a, b) were formed in considerable amounts.The expected products of an electrophilic addition to the triple bond, however, were only found in very minute amounts.The formation of the products obtained was rationalized by heterolysis of the C-Cl bond in the substrate 1 and subsequent reactions of the ensuing intermediate mesomeric cation A.
- Stammann, Guenter,Rehman, Zillur,Griesbaum, Karl
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p. 3103 - 3111
(2007/10/02)
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