Olefinic Double Bond Research Articles

Ru(II) Catalysts Supported by Hydridotris(pyrazolyl)borate for the Hydroarylation of Olefins: Reaction Scope, Mechanistic Studies, and Guides for the Development of Improved Catalysts

Carbon-carbon bond formation is the central method by which synthetic chemists add complexity, which often represents value, to molecules. Uniting a carbon chain with an aromatic substrate to yield an alkyl arene product is thus a molecular means of creating value-added materials. A traditional method for generating alkyl arenes is Friedel-Crafts catalysis, in which an alkyl halide or olefin is activated to react with an aromatic substrate. Unfortunately, despite the development of new generations of solid-state catalysts, the reaction often requires relatively harsh conditions and frequently gives poor to moderate selectivity. Conversely, a halide can first be incorporated into the aromatic ring, and the aryl halide can subsequently be joined by a variety of catalytic coupling techniques. But generating the aryl halide itself can be problematic, and such methods typically are not atom-economical. The addition of aromatic C-H bonds across the C-C double bonds of olefins (olefin hydroarylation) is therefore an attractive alternative in the preparation of alkyl arenes. Despite the dominance and practical advantages of heterogeneous catalysts in industrial synthesis, homogeneous systems can offer an enhanced ability to fine-tune catalyst activity. As such, well-defined homogeneous catalysts for the hydroarylation of olefins provide a potentially promising avenue to address issues of selectivity, including the production of monoalkylated arene products and the control of linear-to-branched ratios for synthesis of long-chain alkyl arenes, and provide access to more ambient reaction conditions. However, examples of homogeneous catalysts that are active for the conversion of unactivated aromatic and olefin substrates to alkyl arene products that function via metal-mediated C-H activation pathways are limited. In this Account, we present results from research aimed at the development of Ru(II) catalysts supported by the hydridotris(pyrazolyl)borate (Tp) ligand for the addition of aromatic C-H bonds across olefins. On the basis of detailed mechanistic studies with TpRu(L)(NCMe)R catalysts, in which the neutral ancillary ligand L is varied, we have arrived at guidelines for the development of improved catalysts that are based on the octahedral-d6 motif.

Efficient Synthesis and Subsequent Transformations of Phenylsulfanylbicyclo[2.2.2]octenones and Phenylselenylbicyclo[2.2.2]octenones

Inverse-electron-demand Diels-Alder reactions of masked o-benzoquinones 2 with phenyl vinyl sulfide and phenyl vinyl selenide furnished highly functionalized bicyclo[2.2.2]octenone derivatives 3 and 4, respectively, in excellent regio- and stereoselectivities and yields up to 90%. The bicyclo[2.2.2]octenone derivatives 3 with the sulfur functionality were subjected to an oxidation-elimination process to furnish bicyclo[2.2.2]octadienone systems 7 in good yields. During the reduction process, the Diels-Alder adducts 3e and 4e led to 8, whereas the carbon-centered radicals generated from the other adducts 3a-d and 4a-d provided various rearranged products 9-13 depending on the substitution pattern and reagents utilized (Raney-Ni or n-Bu(3)SnH). Surprisingly these radicals showed preference for the carbonyl functionality to the olefinic double bond, leading to interesting rearrangement reactions of mechanistic importance and possible synthetic utility. Interestingly the alcohols obtained from the reduction of Diels-Alder adducts 3a-d underwent desulfurization smoothly to give desulfurized products in high yields; thus a detoured method of "reduction-desulfurization-oxidation" provides an entry to desulfurized bicyclo[2.2.2]octenones without rearrangement.

C═C Bond Cleavage on Neutral VO3(V2O5)n Clusters

The reactions of neutral vanadium oxide clusters with alkenes (ethylene, propylene, 1-butene, and 1,3-butadiene) are investigated by experiments and density function theory (DFT) calculations. Single photon ionization through extreme ultraviolet radiation (EUV, 46.9 nm, 26.5 eV) is used to detect neutral cluster distributions and reaction products. In the experiments, we observe products (V(2)O(5))(n)VO(2)CH(2), (V(2)O(5))(n)VO(2)C(2)H(4), (V(2)O(5))(n)VO(2)C(3)H(4), and (V(2)O(5))(n)VO(2)C(3)H(6), for neural V(m)O(n) clusters in reactions with C(2)H(4), C(3)H(6), C(4)H(6), and C(4)H(8), respectively. The observation of these products indicates that the C=C bonds of alkenes can be broken on neutral oxygen rich vanadium oxide clusters with the general structure VO(3)(V(2)O(5))(n=0,1,2...). DFT calculations demonstrate that the reaction VO(3) + C(3)H(6) --> VO(2)C(2)H(4) + H(2)CO is thermodynamically favorable and overall barrierless at room temperature. They also provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes is broken on VO(3)(V(2)O(5))(n=0,1,2...) clusters. A catalytic cycle for alkene oxidation on vanadium oxide is suggested based on our experimental and theoretical investigations. The reactions of V(m)O(n) with C(6)H(6) and C(2)F(4) are also investigated by experiments. The products VO(2)(V(2)O(5))(n)C(6)H(4) are observed for dehydration reactions between V(m)O(n) clusters and C(6)H(6). No product is detected for V(m)O(n) clusters reacting with C(2)F(4). The mechanisms of the reactions between VO(3) and C(2)F(4)/C(6)H(6) are also investigated by calculations at the B3LYP/TZVP level.

Synthesis and characterization of novel cardanol based fulleropyrrolidines

Cardanol oil, a renewable raw material well known by product of the cashew industry, has been used as the starting material for the synthesis of novel fulleropyrrolidines cardanol based. In this work, cardanol has been used as building block for the preparation of target cardanol based precursors obtained by the way of the convenient transformation of the functional groups (aromatic ring, -OH group or the double bonds of the side chain) of the cardanolic structure. Pure 3-n-pentadecylphenol and its derivatives having homogeneous chemical composition, used as the precursor of any fulleropyrrolidines, have been prepared by hydrogenation of the un-saturated side chain and subsequent alkylation of the aromatic ring of cardanol. The reactivity of olefinic double bond present in the side-chain which can undergo easy transformation i.e. oxirane formation as well as metathesis reactions affording various interesting fulleropyrrolidines is also described.

Computational Studies of the Reactions of B10H13− with Alkynes and Olefins: Pathways for Dehydrogenative Alkyne-Insertion and Olefin-Hydroboration Reactions

Quantum mechanical computational studies of possible mechanistic pathways for B10H13(-) dehydrogenative alkyne-insertion and olefin-hydroboration reactions demonstrate that, depending on the reactant and reaction conditions, B10H13(-) can function as either an electrophile or nucleophile. For reactions with nucleophilic alkynes, such as propyne, the calculations indicate that at the temperatures (approximately 110-120 degrees C) required for these reactions, the ground-state B10H13(-) (1) structure can rearrange to an electrophilic-type cage structure 3 having a LUMO orbital strongly localized on the B6 cage-boron. Alkyne binding at this site followed by subsequent steps involving the formation of additional boron-carbon bonds, hydrogen elimination, protonation, and further hydrogen elimination then lead in a straightforward manner to the experimentally observed ortho-carborane products resulting from alkyne insertion into the decaborane framework. A similar mechanistic sequence was identified for the reaction of propyne with 6-R-B10H12(-) leading to the formation of 1-Me-3-R-1,2-C2B10H11 carboranes. On the other hand, both B10H13(-) and 4,6-C2B7H12(-) have previously been shown to react at much lower temperatures with strongly polarized alkynes, and the DFT and IRC calculations support an alternative mechanism involving initial nucleophilic attack by these polyborane anions at the positive terminal acetylenic carbon to produce terminally substituted olefinic anions. In the case of the B10H13(-) reaction, subsequent cyclization steps were identified that provide a pathway to the experimentally observed arachno-8-(NC)-7,8-C2B10H14(-) carborane. The computational study of B10H13(-) propylene hydroboration also supports a mechanistic pathway involving a cage rearrangement to the electrophilic 3 structure. Olefin-binding at the LUMO orbital localized on the B6 cage-boron, followed by addition of the B6-H group across the olefinic double bond and protonation, then leads to the experimentally observed 6-R-B10H13 products.

Structures of Three Chalcones Derived from 6-Methoxy-2-naphthaldehyde

AbstractIn the molecular structures of three new structurally related chalcone derivatives, namely (2E)-1-(2-hydroxyphenyl)-3-(6-methoxy-2-naphthyl)prop-2-en-1-one, C 20 H 16 O 3 , I, (2E)-1-(2-chloropyridin-4-yl)-3-(6-methoxy-2-naphthyl)prop-2-en-1-one, C 19 H 14 ClNO 2 , II, and (2E)-3-(6-methoxy-2-naphthyl)-1-pyridin-4-ylprop-2-en-1-one, III, C 19 H 15 NO 2 , the configuration of the keto group is syn with respect to the olefinic double bond. In all three structures the molecules pack with weak intermolecular C-H···O interactions utilizing both the methoxy and keto oxygen’s in I, the methoxy oxygen in II and the keto oxygen in III. These interactions link the molecules into chains diagonally along the (011) plane of the unit cell in I and III and along the (010) plane in II. The dihedral angle between the phenyl and 2-napthyl rings in I is 31.7(3)°. In II and III the dihedral angle between the pyridyl and 2-naphthyl rings is 14.4(9)° and 1.8(9)°, respectively. C-H···O hydrogen bonding interactions influence these twist angles of these rings in I-III while weak π-π stacking interactions between naphthyl rings in I and III and also between pyridyl and naphthyl rings in II help stabilize crystal packing. [I: P2 1 /c, a = 7.6635(4) A, b = 11.8047(6) A, c = 16.7584(7) A, β = 99.271(5)°, V = 1496.25(13) A 3 ; II: Pbca, a = 14.1424(4) A, b = 6.0957(2) A, c = 33.1458(11) A, V = 2857.43(16) A 3 ; III: P2 1 /c, a = 11.5155(4) A, b = 6.0020(2) A, c = 22.4645(8) A, β = 103.002(4)°, V = 1512.85(9) A 3 ].Index AbstractCrystal structures from three Chalcones derived from 6-methoxy-2-naphthaldehyde are reported and their geometric and packing parameters described.[IMAGE]

Homogeneous Charge Compression Ignition: Formulation Effect of a Diesel Fuel on the Initiation and the Combustion - Potential of Olefin Impact in a Diesel Base Fuel

In this work, attention is paid on initiation and HCCI combustion control through fuel formulation. This article shows the effect of olefin addition (and in particular 1-octene and octa-1,7-diene addition) in a Diesel base fuel. Tests are made with a jet-stirred reactor and an engine bench. The current Diesel fuel cetane numbers are not really adapted for a perfect control of HCCI combustion. In HCCI conditions, the autoignition of a Diesel fuel occurs too early in the cycle. This study shows that, with the jet-stirred reactor, 1-octene addition allows decreasing the advancement of the cool flame reaction of n-octane. Engine bench experiments show that, at 1500 rpm, 1-octene and octa-1,7-diene addition decrease the physical delay and increase the chemical auto-ignition delay of the Diesel base fuel. These results can be explained by olefin chemistry: olefin double bonds imply reactions (with radicals) that are in competition with the cool flame reactions. There is also the fact that the intermediate species are stabilised by mesomery. About pollutants, olefin addition decreases HC emissions of the Diesel base fuel. Adding light olefins in a Diesel base fuel could improving the HCCI combustion.

Mechanistic Study on the Base-Promoted Reaction of Allylphenylsilanes to Alkenylsilanols

Abstract On treatment of allylphenylsilanes with t-BuOK and 18-crown-6 in DMSO, isomerization of the olefinic double bond and subsequent substitution of the phenyl group with a hydroxy group took place smoothly to afford alkenylsilanol derivatives in good yields. The reaction mechanism was investigated using 18O-labeled sulfoxide. We found that a (methylsulfinyl)methyl anion generated from DMSO participated in this reaction.

High throughput experiment approach to the oxidation of propene-to-propene oxide with transition-metal oxides as O-donors

The oxidation of propene-to-propene oxide (PO) has been achieved via oxygen-transfer from transition-metal oxides to the olefin. Under the operative conditions, the cleavage of the olefinic double bond is not observed. The only co-products are acetone (AC) and propinoaldehyde (PA), that can be considered as isomerisation products of propene oxide. The “ parameter space” of the reaction has been investigated using a High Throughput Experiment (HTE) approach. However, it has been shown that the reaction yield and selectivity are sensitive to: temperature, time of the reaction, nature of the metal and its oxidation state and redox potential, lattice energy of the oxide, shape of the oxide (massive or supported), nature of the support, presence of the solvent, and the presence of CO 2. Several metal oxides have been investigated. In this paper, we report the general trend for the tested oxides and discuss in detail the behaviour of PdO x and V 2O 5, either in the massive form or as supported oxides (on alumina or silica). The oxides have been monitored using UV–vis and XPS and the organic products have been identified and determined by GC–MS.

Concerted attack of frustrated Lewis acid–base pairs on olefinic double bonds: a theoretical study

A computational approach reveals cooperative action of the preorganized acidic and basic centers of the frustrated P(t-Bu)(3)/B(C(6)F(5))(3) Lewis pair on olefinic bonds as the key to the observed regioselective addition reaction.

Unusual radical 6-endo cyclization to carbocyclic-ENA and elucidation of its solution conformation by 600 MHz NMR and ab initio calculations

In our previous paper (J. Am. Chem. Soc., 2007, 129, 8362), we reported the synthesis of 7-Me-Carba-LNA and 8-Me-Carba-ENA thymidine through 5-hexenyl or 6-heptenyl radical cyclization. Both 5-hexenyl and 6-heptenyl radical cyclized exclusively in the exo form, giving unwanted exocyclic C7-methyl group. In the present study, we showed that the regioselectivity of the 5-hexenyl radical cyclization could be favorably tuned by introduction of a hydroxyl group to the olefinic double bond, yielding about 9% of the 6-endo cyclization product. Possible pathways to give 6-endo cyclization product 9 compared to the intermediates responsible to give the 5-exo cyclization product 5 has been discussed. Based on this unique 6-endo cyclization strategy, a carbocyclic ENA modified thymidine (carba-ENA) has been successfully synthesized, which also enabled us to perform its full solution conformation analysis by using NMR (1H at 600 MHz) observables for the first time.

糖質の脂質変敗抑制作用メカニズムに関する研究

The mechanism of the suppression of lipid peroxidation by saccharides was investigated. Trehalose effectively inhibited the heat- or radical-induced peroxidation of unsaturated fatty acid (UFA). Several other saccharides, such as sucrose, maltose and neotrehalose, showed negligible effect on the peroxidation, but maltitol's effectiveness was second to that of trehalose. Maltitol inhibited the peroxidation of UFA by its radical-scavenging effect. Thus, among the sugars studied so far, trehalose is a unique antioxidant whose reaction mechanism has not been clarified. We started this study with the hypothesis that trehalose interacts directly with oxidation-sensitive parts of UFA and consequently protects it from the autoxidation. NMR experiments performed, including 1H-1H NOESY measurements, indicated that trehalose selectively interacts with the cis-olefine proton pair in the above UFA with 1 : 1 stoichiometry, and the C-3 (C-3´) and C-6´ (C-6) sites of the sugar are responsible for the interaction. Similar interactions were not observed for the mixtures of the UFA and other saccharides. Quantum chemical study indicates that the OH-3 and OH-6 groups of trehalose bind to the olefin double bonds through OH…π and CH…O types of hydrogen bonds, respectively. Furthermore, the activation energies were calculated for the hydrogen abstraction reactions from the activated methylene group of heptadiene by a methyl radical. The activation energy drastically increased to ca. 30 kcal mol-1 on the complexation with trehalose. These results strongly support the antioxidant mechanism deduced in the previous study and indicate that the formation of unique multiple hydrogen bonds between trehalose and cis-olefin bonds is a rather general event, not confined to the case of UFA. This is the first study to elucidate the antioxidant function of trehalose and maltitol.

2-[(E)-2-(4-Ethoxyphenyl)ethenyl]-1-methylpyridinium iodide monohydrate

In the title compound, C16H18NO+·I−·H2O, the cation is essentially planar, with a dihedral angle of 3.13 (16)° between the pyridinium and benzene rings. The mol­ecule adopts an E configuration with respect to the alkene double bond. In the crystal structure, the cations are packed in an anti-­parallel manner through π–π inter­actions between adjacent pyridinium and benzene rings along the a axis, with centroid-to-centroid distances of 3.615 (2) and 3.630 (2) Å. Water mol­ecules bind the iodide ions through O—H⋯I hydrogen bonds into layers. These layers link with the cations through weak C—H⋯O and C—H⋯I inter­actions.

Solvent-free esterification of poly(vinyl alcohol) and maleic anhydride through mechanochemical reaction

A solid-state mechanochemical processing, that is, pan-milling, was used to conduct the esterification of poly(vinyl alcohol) (PVA) with maleic anhydride (MA) through stress-induced reaction. FTIR spectrum study indicated the presence of ester linkages and olefinic double bonds in maleic anhydride cross-linked PVA. Thermal properties of the cross-linked product were characterized by DSC. The results showed its glass transition temperature was 20 °C higher than the original linear PVA and the thermal stability was also improved.

Facile, Efficient Functionalization of Polyolefins via Controlled Incorporation of Terminal Olefins by Repeated 1,7-Octadiene Insertion

Exclusive repeated insertion of 1,7-octadiene (OD) has been achieved in OD polymerization using (C5Me5)TiCl2(O-2,6-iPr2C6H3)−MAO catalyst to afford polymers containing terminal olefinic double bonds in the side chain. Copolymerization of OD with 1-octene using the same catalyst afforded high molecular weight copolymers containing terminal olefins, and quantitative introduction of hydroxyl group could be achieved upon treatment of the copolymer with 9-BBN/NaOH−H2O2 (aq); ring-opening polymerization of ε-caprolactone could be initiated in a controlled manner from the hydroxyl group after treatment with AlEt3.

Dirhenium carbonyl complexes bearing 2-vinylpyridine, morpholine and 1-methylimidazole ligands

Treatment of the labile compound [Re 2(CO) 8(MeCN) 2] with 2-vinylpyridine in refluxing benzene affords exclusively the new compound [Re 2(CO) 8(μ-η 1:η 2-NC 5H 4CH CH 2)] ( 1) in 39% yield in which the μ-η 1:η 2-vinylpyridine ligand is coordinated to one Re atom through the nitrogen and to the other Re atom via the olefinic double bond. Reaction of [Re 2(CO) 8(MeCN) 2] with morpholine in refluxing benzene furnishes two compounds, [Re 2(CO) 9(η 1-NC 4H 9O)] ( 2) and [Re 2(CO) 8(η 1-NC 4H 9O) 2] ( 3) in 5% and 29% yields, respectively. Reaction of [Re 2(CO) 8(MeCN) 2] with 1-methylimidazole gives [Re 2(CO) 8{η 1-NC 3H 3N(CH 3)} 2] ( 4) and the mononuclear compound fac-[ReCl(CO) 3{η 1-NC 3H 3N(CH 3)} 2] ( 5) in 18% and 26% yields, respectively. In the disubstituted compounds 2 and 4, the heterocyclic ligands occupy equatorial coordination sites. The mononuclear compound 5 consists of three CO groups, two N coordinated η 1-1-methylimidazole ligands and a terminal Cl ligand. The XRD structures of complexes 1, 3 and 5 are reported.

Side-Chain Truncation of Apicularen A by Olefin Cross-Metathesis with Ethylene

The three olefinic double bonds of natural apicularen A (1a) were cleaved by olefin cross-metathesis in the presence of ethylene and Hoveyda-Grubbs catalyst with concomitant E/Z isomerization of Delta(17,18). On extended conversion, 18,19-seco-apicularen A (3) was accumulated and isolated in pure state in 25% yield. In total synthesis, 3 is a valuable late-stage intermediate for side-chain-modified apicularens.

Extensive Isomerization of Alkenes Using a Bifunctional Catalyst: An Alkene Zipper

Catalyzed movement of alkene double bonds up to 30 positions has been accomplished using a catalyst featuring a cationic CpRu fragment and bifunctional imidazolylphosphine. The basic nitrogen of the latter is thought to deprotonate coordinated alkene intermediates reversibly, facilitating isomerization between terminal and (E)-alkenes and accelerating conversions by factors of up to 1 × 104.

New synthesis of aryl β-bromoalkyl sulfones from arenesulfonyl chlorides via cross halogenation

A new procedure has been proposed for the synthesis of aryl β-bromoalkyl sulfones by radical addition of arenesulfonyl chlorides at the double bond of alkenes in the presence of copper(I) halides, sodium bromide, and phase-transfer catalyst. The key stage of the process is bromide ion insertion into intermediate copper(II) derivative formed in the initiation stage. The subsequent bromine atom transfer from copper to alkyl radical yields the addition product.

Reaction between Hydroxycinnamic Acids and Anthocyanin−Pyruvic Acid Adducts Yielding New Portisins

Three new anthocyanin-derived pigments were found to occur in a 2-year-old Port red wine. Their structures were elucidated through LC/DAD-MS and NMR analysis and were found to correspond to a pyranoanthocyanin moiety linked to substituted cinnamyl substituents. The structures of these compounds are very similar to the one already reported for portisins, with a phenolic moiety replacing the catechin moiety. The newly formed anthocyanin-derived compounds display a bathochromic shift of the lambdamax ( approximately 540 nm) when compared with their anthocyanin-pyruvic acid adduct precursor (lambdamax = 511 nm), which may be due to the extended conjugation of the pi electrons in the structures of those pigments. Studies performed in model solutions helped to clarify the formation mechanism of these pigments that can result from the nucleophilic attack of the olefinic double bond of a hydroxycinnamic acid to the eletrophilic C-10 position of the anthocyanin-pyruvic acid adduct, followed by the loss of a formic acid molecule and decarboxylation. The chromatic characterization of these malvidin-3-glucoside-derived compounds revealed a higher resistance to discoloration against the nucleophilic attack by water and bisulfite when compared to malvidin-3-glucoside that is almost converted into its colorless hemiacetal form. However, the resistance to discoloration of these new pigments is not as high as the one reported for catechin-derived portisins. This could be explained by the presence of a smaller group (hydroxycinnamyl group), which does not protect so efficiently the chromophore against nucleophilic attack at the C-2 position. The occurrence of these pigments in red wine highlights new chemical pathways involving anthocyanin-pyruvic acid derivatives as precursors for the formation of new pigments in subsequent stages of wine aging that may contribute to its color evolution.