- Preparation method of 2-methyl-1,3-pentadiene
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The invention relates to a preparation method of 2-methyl-1,3-pentadiene. The preparation method comprises the following steps: in the presence of a supported metal catalyst and a catalyst assistant,carrying out a dehydration reaction on 2-methyl-2,4-pentanediol to obtain 2-methyl-1,3-pentadiene. According to the method, strong acid is not used as a catalyst, so the selectivity of a product is effectively improved, higher yield can be obtained, the problem of equipment corrosion is avoided, the service life of equipment is prolonged, environmental protection benefits are remarkable, and the method is environment-friendly. The 2-methyl-1,3-pentadiene prepared by the method is high in selectivity and high in yield, the generation of a byproduct, namely 4-methyl-1,3-pentadiene is effectivelyreduced, the cyclic application of the catalyst is realized, and the industrial large-scale production of ligustral is facilitated.
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Paragraph 0041-0043; 0049-0051
(2020/11/26)
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- Direct Olefination of Alcohols with Sulfones by Using Heterogeneous Platinum Catalysts
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Carbon-supported Pt nanoparticles (Pt/C) were found to be effective heterogeneous catalysts for the direct Julia olefination of alcohols in the presence of sulfones and KOtBu under oxidant-free conditions. Primary alcohols, including aryl, aliphatic, allyl, and heterocyclic alcohols, underwent olefination with dimethyl sulfone and aryl alkyl sulfones to give terminal and internal olefins, respectively. Secondary alcohols underwent methylenation with dimethyl sulfone. Under 2.5 bar H2, the same reaction system was effective for the transformation of alcohol OH groups to alkyl groups. Structural and mechanistic studies of the terminal olefination system suggested that Pt0 sites on the Pt metal particles are responsible for the rate-limiting dehydrogenation of alcohols and that KOtBu may deprotonate the sulfone reagent. The Pt/C catalyst was reusable after the olefination, and this method showed a higher turnover number (TON) and a wider substrate scope than previously reported methods, which demonstrates the high catalytic efficiency of the present method. Olefination of alcohols: The first heterogeneous catalytic terminal and internal olefination of primary alcohols and methylenation of secondary alcohols with sulfones, a reusable carbon-supported Pt catalyst, and KOtBu is reported (see scheme).
- Hakim Siddiki,Touchy, Abeda Sultana,Kon, Kenichi,Shimizu, Ken-Ichi
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p. 6111 - 6119
(2016/04/26)
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- Z-selective metathesis homocoupling of 1,3-dienes by molybdenum and tungsten monoaryloxide pyrrolide (MAP) complexes
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Molybdenum or tungsten monoaryloxide pyrrolide (MAP) complexes that contain OHIPT as the aryloxide (hexaisopropylterphenoxide) are effective catalysts for homocoupling of simple (E)-1,3-dienes to give (E,Z,E)-trienes in high yield and with high Z selectivities. A vinylalkylidene MAP species was shown to have the expected syn structure in an X-ray study. MAP catalysts that contain OHMT (hexamethylterphenoxide) are relatively inefficient.
- Townsend, Erik M.,Schrock, Richard R.,Hoveyda, Amir H.
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supporting information; experimental part
p. 11334 - 11337
(2012/09/05)
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- Process for dehydrating 2-methylpentane-2,4-diol
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A process for dehydrating 2-methylpentanediol-2,4 to a mixture of 2-methyl-1,3-pentadiene and 4-methyl-1,3-pentadiene at elevated temperature in the presence of an acid catalyst using a polyglycol ether as a heat carrier, wherein a polyglycol ether containing from 80 to 100% by weight of a polyethylene glycol dimethyl ether of the formula CH3(OCH2CH2)nOCH3 where n=2-8 and from 0 to 20% by weight of a polyethylene glycol monomethyl ether of the formula CH3(OCH2CH2)nOH where n=2-8 based in each case on the total mass of polyglycol ether, is used.
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Page/Page column 2-3
(2008/06/13)
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- Gas-phase kinetic and mechanistic studies of some interconverting alkylcyclopropene pairs: Involvement of dialkylvinylidene intermediates and their quantitative behaviour
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The pyrolyses of two isomeric pairs of alkylcyclopropenes, namely 1,3-dimethyl- (15) and 1-ethyl-cyclopropene (16), and 1,3,3-trimethyl- (5) and 1-isopropyl-cyclopropene (17), have been studied in the gas phase. Complete product analyses at various conversions up to 95% were obtained for the decomposition of each compound at five temperatures over a 40°C range. The time-evolution data showed that the isomerisation reactions 15?16 and 5?17 were occurring. Kinetic modelling of each system allowed the determination of rate constants for these and all other decomposition processes. Tests confirmed that all reactions were unimolecular and homogeneous. Arrhenius parameters are reported for overall reactions and individual product pathways. Further kinetic analysis allowed us to extract the propensities (at 500 K) for 1,3-C-H insertion of the dialkylvinylidene intermediates involved in the rearrangements as follows: kprim:ksec: ktert = 1:16.5:46.4. Additional experiments with 13C-labelled cyclopropenes yielded alkyl group migration aptitudes for the dialkylvinylidenes (from the pattern of 13C in the alkyne products) as follows: Me:Et:iPr=1:3.1:1.5. Explanations for these trends are given. Another important finding is that of the dramatic rate enhancements for 1,3-diene product formation from the 1-alkylcyclopropenes; this can be explained by either hyperconjugative stabilisation of the vinylcarbene intermediates involved in this pathway, or their differing propensities to 1,2 H-shift. The observed large variations in product distribution amongst these four cyclopropenes is interpreted in terms of these specific effects on individual pathways.
- Graf Von Der Schulenburg, Wilhelm,Hopf, Henning,Walsh, Robin
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p. 1963 - 1979
(2007/10/03)
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- Catalytic hydromagnesation of di- and polymethyl-substituted 1,3-butadienes
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Hydromagnesation of di- and polymethyl-substituted 1,3-butadienes with alkylmagnesium halides in the presence of Ni(PPh3)2Cl2 and NiPy4Cl2 was studied.
- Viktorov,Zubritskii
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p. 1755 - 1765
(2007/10/03)
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- (E)- And (Z)-1-(Phenylsulfonyl)-4-(trimethylsilyl)-2-butenes: Synthetic Equivalents for the 1-(1,3-Butadienyl) Anion and the 1,1-(1,3-Butadienyl) Dianion
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(E)- and (Z)-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (7 and 8) are converted by n-BuLi to (E)- and (Z)-1-lithio-1-(phenylsulfonyl)-4-(trimethylsilyl)-2-butenes (15 and 16) with retention of initial stereochemistries. Reactions of 15 and 16 with electrophiles (protio and deuterio acids, primary, secondary, and benzyl halides, chloroformates, chlorothioformates, acid chlorides, epoxides, trialkylsilyl chlorides, and triethylgermanyl chloride) in THF or THF/HMPA give the corresponding (E)- and (Z)-1-(phenylsulfonyl)-1-substituted-4-(trimethylsilyl)-2-butenes (32) with stereochemical retention. That β,γ-unsaturated silyl sulfones 32 are formed instead of their α,β-unsaturated (conjugated) isomers are attributed to stabilizing multiple anionic and cationic hyperconjugation and to steric effects as in 29-31. Of importance in synthesis is that 32 are eliminated by TBAF at -20 to 0°C, thermally, or by column chromatography to (E)- (100 to > 93%) rather than (Z)-1-substituted-1,3-butadienes (38). Further, 32 undergo conversions by n-BuLi and various alkylating agents to (unconjugated) 1-(phenylsulfonyl)-1,1-disubstituted-4-(trimethylsilyl)-2-butenes (46) with retention of stereochemistry. Eliminations of 46 by fluoride ion, acid catalysis, or heat yield 1,1-disubstituted-1,3-butadienes (53). Silyl sulfones 7 and 8 are thus synthetic equivalents for the (E)-1-(1,3-butadienyl) anion (44) and the 1,1-(1,3-butadienyl) dianion (57). Silyl sulfones 7 and 8 also undergo efficient stereospecific intramolecular conversions by n-BuLi and α,ω-dihalides to 1,1-cycloalka-1-(phenylsulfonyl)-4-(trimethysilyl)-2-butenes (62 and 71) that are eliminated by fluoride ion, heat, or adsorption chromatography to 1,1-cycloalka-1,3-butadienes (72).
- Meagher, Timothy P.,Yet, Larry,Hsiao, Chi-Nung,Shechter, Harold
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p. 4181 - 4192
(2007/10/03)
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- Gas-phase pyrolysis of several aliphatic 1,3-diols. The kinetic and mechanism of 2,4-dimethyl-2,4-pentanediol
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Satisfactory kinetic determinations of several aliphatic 1,3-diols were difficult to obtain. Moreover the product distributions from each of these substrates suggest complex parallel mechanisms. However, the elimination kinetic of 2,4-dimethyl-2,4-pentanediol has been measured over the temperature range of 419.7-459.9 °C and pressure range of 47-115 torr. The reaction carried out by employing a static system, in seasoned vessel, and in the presence of the free-radical inhibitor propene, proved to be homogeneous, unimolecular, and follows a first-order rate law. The products are acetone, isobutene, and H2O. The rate coefficient is expressed by the following Arrhenius equation: log k1(s-1) = (12.53±0.58)-(217.3±8.0) kJ mol-1 (2.303 RT)-1. The pyrolytic elimination of this substrate is believed to proceed through a concerted six-membered cyclic transition-state type of mechanism.
- Chuchani,Dominguez,Rotinov,Martin
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p. 851 - 854
(2007/10/03)
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- On the regiochemistry of cyclialkylation of regiodefined 4-halo-1-alkenylmetals producing cyclobutenes
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A combination of recently developed anti-carbometallation of homopropargyl alcohols and cyclialkylation of 4-halo-1-alkenyllithiums of appropriate stereochemistry and regiochemistry provides, for the first time, a regiospecific procedure for the synthesis of regiodefined cyclobutenes presumably via σ-type cyclialkylation, whereas carboalumination of 4-halo-1-alkynylmetals containing Si or Al leads to regioconvergent cyclobutene formation.
- Liu, Fang,Negishi, Ei-ichi
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p. 1149 - 1152
(2007/10/03)
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- Polylithiumorganic compounds - 23. 1: 3,4-dilithio-1,2-butadienes by addition of lithium metal to 1,4-unsymmetrically substituted butatrienes
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The synthesis of the highly reactive 1,4-unsymmetrically substituted butatrienes 12a-c is described. When employing a strict synthetic protocol, these alkatrienes react with lithium metal to 3,4-dilithio-1,2-butadienes 20a-c as stable intermediates. The structure of 20 is supported by IR and NMR spectroscopic evidence. The same dianionic intermediate can be prepared in one case by double deprotonation of the 1,2-butadiene 19. Upon derivatization, either 3,4-disubstituted 1,2-butadienes 24, 2,3-disubstituted 1,3-butadienes 25, or 1,4-disubstituted 2-butynes 26 are formed, depending on the nature of the electrophile employed. Copyright
- Maercker, Adalbert,Wunderlich, Hans,Girreser, Ulrich
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p. 6149 - 6172
(2007/10/03)
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- The Kinetics of Pyrolysis of 1,3,3-Trimethylcyclopropene. Evidence for the Involvement of Alkylidene Carbenes in the Thermal Isomerisation of Cyclopropenes
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A low yield of 4-methylpent-2-yne in the gas-phase isomerisation of 1,3,3-trimethylcyclopropene is shown to be more consistent with an alkylidene carbene transient than with a 1,3-biradical intermediate.
- Walsh, Robin,Wolf, Christian,Untiedt, Sven,Meijere, Armin de
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p. 421 - 422
(2007/10/02)
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- Decomposition of 4,4-Dimethylpent-1-ene in the Presence of Oxygen between 400 and 500 deg C: Oxidation Chemistry of Allyl Radicals
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The decomposition of 4,4-dimethylpent-1-ene (DMP) in the presence of O2 has been used as a source of allyl radicals over the temperature range 400-500 deg C.The reaction has been studied in both KCl-coated (peroxy species destroyed at the surface) and aged boric-acid-coated vessels (peroxy species preserved), and the basic mechanism shown to be: (1) (2).Previous studies have shown that 99percent of the t-butyl radicals undergo reaction (2), so that the system is an excellent source of allyl and HO2 radicals.A full product analysis has carried out over a wide range of mixture composition and associated mechanistic aspects discussed.It is shown that allyl radicals are unreactive towards both DMP and O2 and that they react mainly in radical-radical processes. (3) (8) (18).Values of k8/k18 = 0.37, 0.38 and 0.42 are obtained at 400, 440 and 480 deg C, respectively.From a reasonably reliable estimate of and , values of k8 = (3.3 +/- 0.9) * 1E9 and k18 = (7.4 +/- 2.4) * 1E9 dm3 mol-1 s-1 are obtained at 480 deg C.No previous estimates of these rate constants are available in the literature.Values of k4 have been determined and when combined with independent data at higher temperatures give log(A4/s-1) = 14.19 +/- 0.25 and E4 = 255.5 +/- 5.3 kJ mol-1 over the range 400-1025 deg C.DMP -> (CH3)2C=CH2 + CH3CH=CH2 (4).A value of K11 = (2.5 +/- 1) * 1E2 dm3 mol-1 s-1 has been obtained at 480 deg C and shown to be consistent with the reaction's high endothermicity. (11)
- Lodhi, Zulfiqar H.,Walker, Raymond W.
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p. 681 - 689
(2007/10/02)
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- The far-ultraviolet photochemistry of alkylcyclopropenes in solution
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The photochemistry of 1,3,3-trimethylcyclopropene and 1-tert-butyl-3,3-dimethylcyclopropene has been investigated in hydrocarbon, methanol, and 1-hexene solution with far-ultraviolet (185-228 nm) light.Direct photolysis of the two compounds affords allene, alkyne, and 1,3-diene derivatives, formally as a result of initial bond cleavage to yield vinylcarbene intermediates.Products derived from cleavage of the most substituted (C1-C3) cyclopropene bond account for 60-80percent of the observed mixture in each case.Results from the photolysis of 1,3,3-trimethylcyclopropene-1-13C suggest a second pathway for formation of alkyne products in cyclopropene photochemistry, which occurs in competition with (or by exclusion of) the vinylcarbene -hydrogen migration pathway.The data are consistent with the intermediacy of a vinylidene species, formed by -hydrogen migration/ring opening, although attempts to chemically trap this intermediate with methanol or alkene were unsuccessful.Key words: cyclopropene, photolysis, vinylmethylene, propenylidene, far-UV.
- Fahie, Brian J.,Leigh, William J.
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p. 1859 - 1867
(2007/10/02)
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- 1-ISOPROPYLALLYLOXYCARBONYL (IPAoc) AS A PROTECTIVE GROUP OF AMINES AND ITS DEPROTECTION CATALYSED BY PALLADIUM-PHOSPHINE COMPLEX
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As a new protective group of amines, 1-isopropylallyloxycarbonyl (IPAoc) group was developed.IPAoc group can be removed by treatment with a palladium-phosphine catalyst forming carbon dioxide and 4-methyl-1,3-pentadiene by the decarboxylation and β-hydrogen elimination of (?-1-isopropylallyl)-palladium intermediate under neutral condititons.The present protection-deprotection was applied to a one-pot peptide synthesis.
- Minami, Ichiro,Yuhara, Masami,Tsuji, Jiro
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p. 2737 - 2740
(2007/10/02)
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- AlPO4-Al2O3 PROMOTED CYCLODEHYDRATION OF DIOLS
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A convenient method for the preparation of cyclic ethers by distillation of diols over solid AlPO4-Al2O3 is presented.
- Costa, A.,Riego, J. M.
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p. 1373 - 1376
(2007/10/02)
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- Isomerisation des radicaux insatures. III. Radicaux α,α,β-, α,β,γ- et α,α,γ-trimethallyles
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α,α,β-, α,β,γ-, and α,α,γ-trimethallyl radicals have been generated in the 147.0-nm gas phase photolysis of 2,3,3-trimethyl-1-butene, 3,4-dimethyl-2-pentene, and 2,4-dimethyl-2-pentene, respectively.Under these conditions, the majority of allyl radicals have an internal energy sufficient for further decomposition: they give rise to the formation of various 1,3-dienes and small amounts of either 1,2- or 2,3-dienes.An internal sigmatropic 1,2-hydrogen atom transfer process is part of the proposed mechanism to explain such products.Moreover, the fragmentation of the trimethyl substituted allyl radicals involves the split of one β(C-C) bond, then one β(C-H), and, to a lesser extent, one central C-CH3 bond.
- Deslauriers, Helene,Collin, Guy J.
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p. 3168 - 3173
(2007/10/02)
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- Gas-Phase Pyrolysis Kinetics of 5-Acetoxy-2-methylpent-2-ene
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The kinetics of the gas-phase pyrolysis of 5-acetoxy-2-methylpent-2-ene has been measured over the temperature range 330-380 deg C and pressure range 53-210 torr.The reaction, in a static system seasoned with allyl bromide, and in the presence of propene inhibitor, is homogeneous, obeys a first-order law, and is unimolecular.The rate constants are given by the Arrhenius equation log k(s-1) = (13.21+/-0.14)-(199.6+/-1.7)kJ mol-1(2.303RT)-1.The presence of the (CH3)2C=CH group at the β-carbon atom of ethyl acetate does not provide anchimeric assistence in the elimination of this ester.A simultaneous effect of both steric acceleration and the allylic weakening of the β hydrogen appears to cause a slight rate enhancement of the Z=(CH3)2C=CH group relative to Z=CH2=CH group in the pyrolysis of ZCH2CH2OAc.
- Chuchani, Gabriel,Martin, Ignacio,Alonso, Miguel E.
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p. 1241 - 1243
(2007/10/02)
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- Etude des transformations catalytiques sur alumine de β-tetrahydrofurylmethanols
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The products obtained by treatment of β-tetrahydrofurylmethanols at 310-330 deg C, using alumina as catalyst are studied.The nature of the products-furans, tetrahydrofurans, aliphatic and cyclic dienes-shows that beside the simple dehydration side reactions take place leading, as the case may be, to dehydrogenation, raduction, ring opening and fragmentation.
- Infarnet, Yves,Accary, Armand,Huet, Jean
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p. 261 - 266
(2007/10/02)
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- Mechanistic Aspects of Gas-Phase Photodecarbonylation Reactions of Bicyclohexanones
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The gas-phase photodecarbonylation and photofragmentation reactions of substituted bicyclohexan-3-ones have been studied in detail.Photolysis of these ketones yields 1,3-dienes, vinylcyclopropanes, and 1,4-dienes as detectable products.The possible mechanisms for these reactions are discussed in light of the regiochemical and stereochemical results obtained.In addition, methyl substitution at C-6 and C-2 of these ketones has been shown to have a pronounced effect on both product ratios and overall reaction efficiency.These effects are discussed in terms of stereoelectronic and electronic controls of rates of cyclopropane ring opening of intermediate acylcyclopropylcarbinyl diradicals.
- Mariano, Patrick S.,Bay, Elliott,Watson, Darrell G.,Rose, Timothy,Bracken, Christopher
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p. 1753 - 1762
(2007/10/02)
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