Showing papers on "Alkene published in 1998"
TL;DR: The catalytic production of organic molecules is one of the most important applications of organometallic chemistry and enantioselective syntheses of molecules bearing an amine functionality use classical stoichiometric reactions with chiral auxiliaries or utilize enantiomerically pure starting material.
Abstract: The catalytic production of organic molecules is one of the most important applications of organometallic chemistry. For this purpose the distinct reaction chemistry of organic ligands covalently bound to transition metals is exploited. Most organometallic chemistry has focused on the formation of carboncarbon or carbon-hydrogen bonds. The platinum group metals, in particular Pd and Rh, have been the most commonly used elements insfrequently commercializedscatalytic processes that include hydrogenation, hydroformylation and others. On the other hand, carbon-oxygen and carbon-nitrogen bonds are found in the majority of organic molecules and are of particular importance in physiologically active substances. However, catalytic organometallic reactions that lead to the formation of carbonheteroatom bonds are less common.1,2 The catalytic construction of carbon-nitrogen bonds in amines is particularly rare.3-10 Clearly, efficient catalytic routes to nitrogen based molecules are of great interest.11 Especially useful are catalytic hydroaminations of olefins and alkynes which avoid production of byproducts, like salts, generally observed in metal-catalyzed aminations of C-X derivatives (X ) e.g., halogen). However, known aminations of olefins often require stoichiometric use of transition metals and general methods for carrying out aminations catalytically are not yet available.12,13 Most of the present enantioselective syntheses of molecules bearing an amine functionality use classical stoichiometric reactions with chiral auxiliaries or utilize enantiomerically pure starting material.14-16 Hydroamination of alkenes and alkynes, which constitutes the formal addition of a N-H bond across a carbon-carbon multiple bond (Scheme 1), is a transformation of seemingly fundamental simplicity and would appear to offer the most attractive route to numerous classes of organo-nitrogen molecules such as alkylated amines, enamines or imines. Organic chemists have developed various synthetic approaches for the amination of olefins.17-19 Direct addition of nucleophiles H-NR2 to activated alkenes is of general importance for the synthesis of compounds with nitrogen atoms â to groups such as keto, ester, nitrile, sulfoxide, or nitro.13,20-23 These additions usually lead to the anti-Markovnikov products. On the other hand aliphatic olefins as well as most aromatic olefins are often aminated to give the Markovnikov product. One possibility to reverse the reactivity of aliphatic olefins is the use of electrophilic nitrogen radicals which have been used to obtain anti-Markovnikov products.24 In the past much work has been done on the activation of alkenes with stoichiometric amounts of metal.24 Reactions are mostly promoted by complexes of titanium,25 iron,26 zirconium,27 palladium28-31 and mercury.32,33 However, catalytic additions of amines H-NR2 to nonactivated double or triple bonds are still rare. Two basic approaches have been employed to catalytically effect aminations and involve either alkene/alkyne or amine activation routes (Scheme 2).34,140 Alkene activation is generally accomplished with late-transition-metal catalysts, which render coordinated olefins more susceptible to attack by † Dedicated to Dipl. Chem. Martin Eichberger (deceased 11/20/ 1997). 675 Chem. Rev. 1998, 98, 675−703
1,268 citations
TL;DR: In this paper, formal total synthesis of metacycloprodigiosin (2) and streptorubin B (3) is described, where the key step en route to their meta-bridged pyrrole core structures consists of a metathesis reaction of electron-deficient enynes catalyzed by either platinum halides, hard Lewis acids, or HBF4.
Abstract: Formal total syntheses of the antibiotics metacycloprodigiosin (2) and streptorubin B (3) are described, which are known to exhibit promising immunomodulating properties. The key step en route to their meta-bridged pyrrole core structures 5 and 7, respectively, consists of a metathesis reaction of electron-deficient enynes catalyzed by either platinum halides, hard Lewis acids, or HBF4. This transformation expands the pre-existing cycloalkene of the substrates by two C atoms, forges the bicyclic pyrrolophane structure of the targets, and simultaneously forms a bridgehead alkene function. The products of this skeletal rearrangement are converted into the targets by a sequence comprising (i) a stepwise reduction of their enone entity to the corresponding saturated alcohols and (ii) an aromatization of the N-tosylated dihydropyrroles 20 and 34 thus obtained via elimination of potassium sulfinate on exposure to KAPA (potassium 3-aminopropylamide). A careful analysis of the minor byproducts formed in the enyne...
332 citations
TL;DR: In this paper, various titanium complexes of the type Cp‘Ti(OAr)Cl2 (Cp = cyclopentadienyl; OAr = aryloxy) could be prepared in high yields from CpTiCl3.
217 citations
TL;DR: Alkene metathesis in organic synthesis is a well-established research area in organometallic chemistry that involves the rearrangement of carbon atoms in alkenes.
Abstract: Organometallic chemistry is a well established research area at the interface of organic and inorganic chemistry. In recent years this field has undergone a ren aissance as our understanding of organo
175 citations
TL;DR: In this paper, the properties of Cp2Zr(n-Bu)2, CpZrEt2, and Cp 2Zr (t-Bu)(i-Bu), as well as their structures are reviewed.
Abstract: Dialkylzirconocenes in situ generated such as Cp2Zr(n-Bu)2, Cp2ZrEt2, and Cp2Zr(t-Bu)(i-Bu) are thermolyzed to afford zirconocene-alkene complexes. In the cases of Cp2Zr(n-Bu)2 and Cp2Zr(t-Bu)(i-Bu), Cp2Zr-alkene complexes generated from them tend to act as a “Cp2Zr” equivalent, since the initially generated alkene is often replaced by another π-bond containing compound. In the presence of alkynes, for example, alkyne complexes may be generated. On the other hand, Cp2Zr(ethylene) tends to serve as an intermediate since the ethylene moiety is often incorporated in the final organic products. Ring expansion and contraction, ligand substitution, transmetallation, migratory insertion, stereoisomerization, regioisomerization, oxidative addition involving these Cp2Zr-alkene and Cp2Zr-alkyne complexes as well as their structures are reviewed.
165 citations
TL;DR: The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide as mentioned in this paper.
Abstract: The catalytic potential of aluminum-free zeolite titanium beta (Ti-beta) is demonstrated by its facile catalysis of the epoxidation of alkenes with aqueous hydrogen peroxide. The Ti-beta catalyst is compared with TS-1, Ti,Al-beta and Ti-MCM-41 in the epoxidation of 1-octene and norbornene. The advantage of the larger pore size of Ti-beta is illustrated by the facile epoxidation of norbornene in which TS-1 displayed no activity. Rate differences in the epoxidation of terminal or internal alkenes are very small for Ti-beta, indicating that the Ti-site is rather spacious. The catalytic properties of Ti-beta were further investigated in the epoxidation of bulky alkenes such as cyclohexenes, cyclic terpenes and allylic alcohols. Ti-beta was found to catalyze the epoxidation of a wide variety of alkenes with aqueous hydrogen peroxide. In the epoxidation of linear alkenes two trends were observed. The lower alkenes were epoxidized fastest and the internal alkenes were slightly faster than the alkenes with a terminal double bond. The reactivity of methylenecyclohexane is about twice that of 1-methylcyclohexene. Based on electronic effects of substituents the reverse order would be expected, which suggests that here steric effects at the titanium site can play a dominant role in determining reactivity. Pronounced electronic effects were observed to be more important in the epoxidation of allylic alcohols: more highly substituted allylic alcohols are more reactive, whereas the reactivity of the substrates bearing a terminal, unsubstituted double bound is over an order of lower magnitude.
138 citations
TL;DR: The Ru/M-41(m) catalyst can be used repeatedly, and 67% of its initial activity is retained after 11 691 turnovers (three runs), the loss of activity is attributed to catalyst leaching and/or deactivation.
Abstract: A ruthenium complex of meso-tetrakis(2,6-dichlorophenyl)porphyrin, [RuII(TDCPP)(CO)(EtOH)], is immobilized into mesoporous MCM-41 molecular sieves; the supported Ru catalyst can effect highly selective heterogeneous alkene epoxidations using 2,6-dichloropyridine N-oxide as terminal oxidant. Aromatic and aliphatic alkenes can be efficiently converted to their epoxides in good yields and selectivities, and cis-alkenes such as cis-stilbene, cis-β-methylstyrene, and cis-β-deuteriostyrene are epoxidized stereospecifically. Oxidation of cycloalkenes, e.g., norbornene and cyclooctene, can be carried out effectively using the heterogeneous Ru-catalyzed reaction while these alkenes are unreactive in the zeolite-based titanium silicate (TS-1)-catalyzed conditions (Murugavel, R.; Roesky, H. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 477). On the other hand, the Ru/M-41(m) catalyst displays size selectivity in the (+)-limonene oxidation where the terminal CC bond (vs internal trisubstituted CC bond) becomes more readi...
130 citations
TL;DR: In this paper, the ozone reaction with isoprene, α-pinene, and methyl vinyl ketone was measured using the recently developed small-ratio relative-rate technique, which uses small amounts of fast-reacting aromatics and aliphatic ethers to trace OH formation.
Abstract: OH radical formation from the ozone reaction with isoprene, α-pinene, and methyl vinyl ketone were measured using the recently developed small-ratio relative-rate technique. This method uses small amounts of fast-reacting aromatics and aliphatic ethers to trace OH formation. Measured OH yields were 0.25±0.06, 0.70±0.17, and 0.16±0.05 for isoprene, α-pinene, and methyl vinyl ketone, respectively. The levels of biogenic alkenes necessary to contribute a non-negligible fraction of new OH, HO2, and RO2 radicals are briefly discussed.
109 citations
TL;DR: The reaction of [L2Rh(acac)] (L = alkene or phosphine) with B2cat3 yield the zwitterionic complexes [L 2Rh(η6-catBcat)] and [(acac)Bcat] cleanly; [(dppm)Rh(πm)BCat)], the X-ray structure of which is reported, is an excellent catalyst for the diboration of vinylarenes and unstrained internal alkenes cis-and trans-stilbene and trans-β-
105 citations
TL;DR: In this article, a water-soluble diphosphine based on a xanthene-type backbone was used for two-phase alkene hydroformylation, which led to the selective formation of linear aldehydes, hex-1-ene and 4-styrenesulfonate.
Abstract: The concept of a large `natural' bite angle in chelating diphosphines has been extended to two-phase alkene hydroformylation by the use of a water-soluble diphosphine based on a xanthene-type backbone. The recently developed diphosphine Xantphos was modified with water-soluble groups by controlled sulfonation in fuming sulfuric acid to form 2,7-bis(SO 3 Na)-4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (2,7-bis(SO 3 Na)-Xantphos) exclusively. The application of this ligand in the two-phase rhodium-catalyzed hydroformylation of alkenes led to the selective formation of linear aldehydes. Some data are reported on the hydroformylation of propene, hex-1-ene and 4-styrenesulfonate. Recycling experiments showed the catalyst to be active up to five cycles. For comparison, the two-phase catalytic results are also given with TPPTS as the ligand. Furthermore, the coordination behaviour of the in situ formed catalytic species HRh(2,7-bis(SO 3 Na)-Xantphos)(CO) 2 was studied by high-pressure NMR spectroscopy which indeed showed the desired bis-equatorial coordination of the ligand to the rhodium center.
103 citations
TL;DR: The use of soluble polymeric ligands for homogeneous catalysts separation is reviewed with emphasis on work from the author's laboratory in this paper, where the utility of these systems is also discussed in the broader context of polymer-supported catalysis.
Patent•
6 Nov 1998TL;DR: In this article, a process for the production of C 8 alkene isomers by the oligomerization of light olefins to heavier olefs is improved by the addition of heavy paraffins to the oligomers.
Abstract: A process for the production of C 8 alkene isomers by the oligomerization of light olefins to heavier olefins is improved by the addition of heavy paraffins to the oligomerization zone. The recycle of the heavy paraffins improves the selectivity of the oligomerization for C 8 olefin isomers that have a high octane number when saturated and reduces catalyst fouling. The saturated octane number of the resulting C 8 isomers is particularly improved when the oligomerization zone is operated at reduced temperature conditions.
TL;DR: In this paper, the isomerization of n-hexane over Pt-loaded H-β zeolites was investigated, and it was shown that 1-hexene produced by the dehydrogenation of hexane at the metal component is not directly involved in the reaction.
TL;DR: In this paper, the yields of hydroxy nitrates from the reaction of selected C2−C6 alkenes with OH in the presence of NO were measured at 296 ± 3 K in a 9600 L photochemical smog chamber.
Abstract: The yields of hydroxy nitrates from the reaction of selected C2−C6 alkenes with OH in the presence of NO were measured at 296 ± 3 K in a 9600 L photochemical smog chamber. Hydroxyl radicals were produced from the photolysis of isopropyl nitrite in the presence of NO. The loss of the alkene was followed using gas chromatography. The hydroxy nitrate products were determined using a combination of capillary chromatography and an organic nitrate specific chemiluminescence detector. The yield of hydroxy nitrates was observed to increase with the size of the precursor alkene as follows: ethene (0.86%), propene (1.5%), 1-butene (2.5%), cis-2-butene (3.4%), and 1-hexene (5.5%). Previous studies involving the production of alkyl nitrates from alkanes show a similar trend, but the yields reported here are a factor of 2−3 lower than for the corresponding simple alkylperoxy radical. The impact of a β-hydroxy group on the nitrate yield is examined using an ab initio molecular orbital study. It indicates that a hydrog...
TL;DR: In this paper, the information is classified in terms of type of catalysis and each type is subdivided according to the metal used, so that a reactivity pattern might emerge to guide future developments.
TL;DR: The reactions of hydroxyl radical with ethene, fluoroethene, and chloroethene have been studied by quantum chemical methods as mentioned in this paper, and the convergence of barrier heights and reaction enthalpies has been systematically investigated with respect to the size and quality of basis set and the treatment of correlation energy.
Abstract: The reactions of hydroxyl radical with ethene, fluoroethene, and chloroethene have been studied by quantum chemical methods Reactants, prereaction complexes, transition-state structures, and products were optimized and vibrational frequencies were calculated at the UMP2/6-311+G(2d,p) level Transition-state structures are significantly different from the prereaction complexes formed on the reactant side of the MEP The convergence of barrier heights and reaction enthalpies has been systematically investigated with respect to the size and quality of basis set and the treatment of correlation energy The best agreement with experimental results is found at the MP2/aug-cc-pVTZ level of theory Regioselectivity is discussed in terms of two properties of the radical and the investigated alkenes The first factor is the relative spin density in the 3ππ* state of the alkene The second factor is the relative strengths of the product C−O bond, ie, relative stability of the corresponding radical product In the
TL;DR: In this paper, a cis/trans mixture of isomers is obtained when the pure compounds are treated with iodine and the polymeric trans form of 1 transforms into the dimeric cis form when irradiated with UV light.
Abstract: Cis/trans isomerization of the alkene in these pyridine-functionalized porphyrins results in a reorganization of the molecular architecture: the polymeric trans form of 1 transforms into the dimeric cis form when irradiated with UV light. A cis/trans mixture of isomers is obtained when the pure compounds are treated with iodine.
TL;DR: In this article, the production mechanism of light alkenes, alkanes, and isoprene was investigated in laboratory experiments by measuring their concentrations in natural seawater as a function of spectral range, exposure time and origin, and concentration of dissolved organic carbon (DOC).
Abstract: The production mechanism of light alkenes, alkanes, and isoprene was investigated in laboratory experiments by measuring their concentrations in natural seawater as a function of spectral range, exposure time and origin, and concentration of dissolved organic carbon (DOC). The production mechanism of alkanes and of isoprene could not be clarified. Ethene and propene are produced photochemically from DOC. The relevant spectral range is UV and short-wavelength visible light. Initial production rates (up to day 10 of exposure) were in the range of several pmol L−1 h−1 (mg DOC)−1; the corresponding mean quantum yields for the spectral range of 300–420 nm were about 10−8. Generally, the production rates and the quantum yields for ethene were about 2 times that of propene. The key factors in the total column integrated oceanic alkene production are the solar photon flux at sea surface, the penetration depth of the light into the ocean (especially the relation between different light absorbers, i.e., the extinction due to absorption of DOC), and the wavelength- and DOC-dependent quantum yields. As a result of the high variability of these parameters, actual local alkene production rates for a specific oceanic region may differ considerably from the globally averaged oceanic alkene production rates. The latter were estimated to be at most 5 Mt yr−1.
TL;DR: In this paper, a series of zeolite, amorphous silica-alumina (ASA) and ordered mesoporous aluminium-containing micelle templated silica (MTS) catalysts were investigated for butene oligomerization.
Abstract: The oligomerization of butene at 423 K and 1.5–2 MPa has been investigated over a series of zeolite, amorphous silica–alumina (ASA) and ordered mesoporous aluminium-containing micelle templated silica (MTS) catalysts. While olefin oligomerization into strongly adsorbed residue and fast deactivation prevailed on microporous catalysts and ASA, mesoporous aluminosilicates with uniform pore openings near 3 nm in size exhibited high selectivity and good stability with time for the production of branched dimers. The characterization of the surface properties of the solids, the nature of the adsorbed residue on the spent catalysts, and the identification of reaction intermediates by in situ infrared spectroscopy of co-adsorbed acetonitrile and butene, suggest that the unique catalytic behaviour of MTS-type catalysts is related to the moderate strength and the high dispersion of the acid sites in the mesoporous structure.
TL;DR: In this article, a preparative TMAH thermochemolysis of humin and humic acids yields various hydrocarbons (alkene/alkane doublets, sterenes, hopenes and hopanes), methyl esters of linear and branched fatty acids, linear dicarboxylic acids, ω-methoxy fatty acids and 1-mETHoxyalkanes).
TL;DR: In this paper, the regioselectivity of monosubstituted alkene hydrosilylation catalyzed by organolanthanide and group 3 organometallic complexes has been studied as a function of catalyst structure.
TL;DR: Biphase systems were generated by combining toluene solutions of alkenes (2-cyclohexen-1-one, 1-dodecene, cyclododecenes, 4-bromostyrene) and CF 3 C 6 F 11 solutions of the pre-catalyst ClRh[P(CH 2 CH 2 (CF 2 ) 5 CF 3 ) 3 ] 3 (( 1 ); 1.1-0.8") and placed under 1m of H 2.
TL;DR: In this article, the Schrock and Grubbs Cl2(Cy3P)2RuCHPh (2) carbenes gave diverse monocyclic and bicyclic β-lactam dienes including derivatives of 1-azabicyclo[4.2.0]octan-8-one, 1-aza-1-cyclo[5.2]nonan-9-one and its 6-thia, 6-aza, and 6-oxa analogues.
Abstract: 4-Acetoxy-2-azetidinone and (3R,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethylsilyl)-oxyethyl]-2-azetidinone were converted into 4-alkenyloxy-, 4-(N-allyltoluene-4-sulfonamido)-, 4-(allylthio)-, and 4-alkenyl-2-azetidinone systems. In addition, 4-acetoxy-2-azetidinone and (3R,4R)-4-acetoxy-3-[(1R)-1-(tert-butyldimethylsilyl)-oxyethyl]-2-azetidinone were converted into β-lactam dienes via sequential C-4 substitution using unsaturated alcohols, allyl mercaptan, N-allyltoluene-4-sulfonamide, and allyl(chloro)dimethylsilane followed by N-allylation. Crossed metathesis of β-lactam alkenes with styrene partners and ring closing metathesis of β-lactam dienes using the Schrock [(CF3)2MeCO]2Mo(CHCMe2Ph)(NC6H3-2,6-iso-Pr2) (1) or Grubbs Cl2(Cy3P)2RuCHPh (2) carbenes gave diverse monocyclic and bicyclic β-lactam systems including derivatives of 1-azabicyclo[4.2.0]octan-8-one, 1-azabicyclo[5.2.0]nonan-9-one and its 6-thia, 6-aza, and 6-oxa analogues, 7-oxa-1-azabicyclo[6.2.0]octan-10-one, 8-oxa-1-azabicyclo[7.2.0]octan-...
TL;DR: The results indicate that methallyl alkenes and styrenes can function as good substrates and many of the epoxide products derived from chloroperoxidase catalysis can serve as chiral synthons for drug and natural product synthesis.
Abstract: Recent experiments from several laboratories have shown that chloroperoxidase is able to catalyze a broad spectrum of stereoselective hydroxylation, sulfoxidation and epoxidation reactions. Our laboratory has investigated the substrate specificity of chloroperoxidase for chiral epoxidation of mono- and disubstituted alkenes. Chloroperoxidase is able to efficiently utilize alkenes having chain lengths of nine or fewer carbon atoms except for monosubstituted olefins which often function as reversible suicide inhibitors of the enzyme. Excellent substrates are created by cis-1-methyl and 2-methyl substitutions on the olefinic double bond. Kinetic, enantioselectivity and epoxide yield data have been obtained on a series of brominated and unbrominated methallyl alkenes and substituted styrenes. The results indicate that methallyl alkenes and styrenes can function as good substrates. Km values for the methallyl substrates are in the millimolar range and the Vmax's reach turnovers of 200 per min. Hammett plot data are consistent with the formation of a radical as opposed to a carbocation intermediate in the rate determining step in the epoxidation of substituted styrenes. Many of the epoxide products derived from chloroperoxidase catalysis can serve as chiral synthons for drug and natural product synthesis.
TL;DR: Treatment of PdCl2(MeCN)2 and CuCl with N,N-dimethylformamide (DMF) under O2 gives polymeric complex [(PdCl 2)2CuCl2 (DMFs)4]n (1) and Pd-Cu heterometallic complex 2 containing O atom derived from molecular oxygen.
TL;DR: Palladium nanoclusters were synthesized within microphase-separated diblock copolymer films of [MTD] 113 [Pd(Cp N )PA] 50 (MTD=methyltetracyclododecene, Cp N = endo -2-(cyclopentadienylmethyl)norborn-5-ene, PA= η 3 -1-phenylallyl) as discussed by the authors.
TL;DR: In this article, an unsymmetrical transition structure for 1,3-butadiene with an order of magnitude difference in the carbon−oxygen bond distances of 0.305 A at the QCISD/6-31G* level was found.
Abstract: The epoxidations of propene and isobutene with peroxyformic acid proceed by a concerted pathway via slightly unsymmetrical transition structures where the differences in the bond distances between the double-bond carbons and the spiro oxygen are only 0.021 and 0.044 A at the QCISD/6-31G* level. In contrast, the more polarizable nature of the carbon−carbon double bond of α,β-unsaturated systems results in an unsymmetrical transition structure for the epoxidation of 1,3-butadiene with an order of magnitude difference in the carbon−oxygen bond distances of 0.305 A at the QCISD/6-31G* level. A highly unsymmetrical transition structure has been also found at this level for the epoxidation of acrylonitrile. Notwithstanding the difference in the extent of asymmetry of the transition structures, both epoxidations of methyl-substituted alkenes and such α,β-unsaturated systems as 1,3-butadiene and acrylonitrile with peroxyformic acid follow a concerted asynchronous pathway. An unsymmetrical transition structure for...
TL;DR: This article showed that Cs2.5H0.5PW12O40 is an efficient water-tolerant solid acid, which can be reused five times for the hydrolysis of ethyl acetate repeatedly.
TL;DR: In this paper, the same cation has been fully characterised by 1H, 13C NMR and 1H DNMR spectroscopy using 1H-DNMR spectrograms.
TL;DR: In this article, the influence of acid sites for isobutane/n-butene alkylation on zeolite BEA with varying degrees of Na+ ion exchange is reported.