Double Bond Isomerization Research Articles

Gold(I)-catalyzed 1,2-acyloxy migration/[3+2] cycloaddition of 1,6-diynes with an ynamide propargyl ester moiety: highly efficient synthesis of functionalized cyclopenta[b]indoles.

A gold-catalyzed cycloisomerization of 1,6-diynes containing an ynamide propargyl ester or carbonate moiety has been developed that provides an attractive route to a diverse-substituted 3-acyloxy-1,4-dihydrocyclopenta[b]indoles. Mechanistic studies indicate that the reaction likely proceeds through a competitive 1,2-OAc migration followed by [3+2] cycloaddition of the vinyl gold-carbenoid intermediate with the pendant triple bond. The synthetic utility of the obtained cyclopenta[b]indole products was demonstrated by their efficient transformations by deprotection or double-bond isomerization reactions.

Solid base catalysts: fundamentals and their applications in organic reactions

Solid base catalysis studied over the last a half of century is reviewed briefly including mainly those performed in our laboratories. The review begins with advantages of solid base catalysts over homogeneous base catalyst in industrial use followed by definition of Brϕnsted base and Lewis base. The materials known as solid base catalysts are listed, and four reasons for which these materials are recognized as solid base catalyst are explained. For all solid base catalysts, variations in activity as a function of pretreatment temperature show a volcano shape; an incline with the temperature results from an appearance of basic sites by removal of water and carbon dioxide from the surface and a decline results from an elimination of basic sites by rearrangement of surface atoms. The reactions catalyzed by solid base catalysts can be classified into three types: double bond isomerization, addition of anion and proton to various double bonds, and alcohol decomposition. These are represented by 1-butene isomerization, hydrogenation of conjugated 1,3-butadiene and dehydration of 2-butanol. Their mechanisms are explained. In addition, bifunctional base-catalyzed reactions in which basic sites participate in one step of successive steps are exemplified for methyl isobutyl ketome synthesis, metathesis, Tishchenko reaction and side-chain alkylation of toluene. Some industrial processes and future perspectives are briefly described.

Metathesis reactions of rapeseed oil‐derived fatty acid methyl esters induced by monometallic and homobimetallic ruthenium complexes

In this study, homobimetallic ruthenium alkylidene complexes were used for the self‐metathesis and ethenolysis reactions of methyl oleate and rapeseed oil‐derived FAME mixtures. The activity and selectivity of homobimetallic ruthenium alkylidene complexes were also compared with their monometallic analogs. It has been determined that homobimetallic complexes bearing phosphine and N‐heterocyclic carbene ligands are more active and selective catalysts than their monometallic analogs for self‐metathesis and ethenolysis reactions of rapeseed FAME mixture. Homobimetallic ruthenium complexes showed superior selectivity at 25°C toward these reactions. Conversion values of 99% with 96% selectivity toward ethenolysis products were observed by using homobimetallic ruthenium complexes. In addition to these superiorities, relatively lower amounts of double bond isomerization side‐products were obtained by using homobimetallic complexes. This catalytic approach represents a unique example for metathesis transformation of FAME mixtures at relatively low temperature (25°C) and ethylene pressure (1 atm) with high selectivity using homobimetallic ruthenium alkylidene complexes.Practical applications: This study reports the selective transformation of rapeseed oil‐derived FAME by ethenolysis reactions catalyzed by homobimetallic ruthenium alkylidene complexes. Industrially important terminal olefins as well as new polymer precursors can be synthesized in a selective manner using these catalytic systems.Ethenolysis reactions of rapeseed oil‐derived fatty acid methyl ester mixture, catalyzed by homobimetallic ruthenium alkylidene complexes exhibit high selectivity at RT.

Nickel-Exchanged Zincosilicate Catalysts for the Oligomerization of Propylene

Two nickel-containing zincosilicates (Ni-CIT-6 and Ni–Zn-MCM-41) and two nickel-containing aluminosilicates (Ni-HiAl-BEA and Ni-USY) are synthesized and used as catalysts to oligomerize propylene into C3n (C6 and C9) products. Both Ni-CIT-6 and Ni-HiAl-BEA have the *BEA topology and are investigated to assess the effects of framework zinc versus aluminum because the former gives two framework charges per atom, whereas the latter, only one. Ni-CIT-6 and Ni–Zn-MCM-41 enable the comparison of a microporous to a mesoporous zincosilicate. Ni2+ ion-exchanged into zeolite Y has been previously reported to oligomerize propylene and is used here for comparison. Reaction data are obtained at 180 and 250 °C, atmospheric pressure, and WHSV = 1.0 h–1 in a feed stream of 85 mol % propylene (in inert). At these conditions, all catalysts are capable of oligomerizing propylene with steady-state conversions ranging from 3 to 16%. With the exception of Ni-HiAl-BEA, all catalysts have higher propylene conversions at 250 °C than at 180 °C. Both *BEA materials exhibit similar propylene conversions at each temperature, but Ni-HiAl-BEA is not as selective to C3n products as Ni-CIT-6. Zincosilicates demonstrate higher average selectivities to C3n products than the aluminosilicates at both reaction temperatures tested. Hexene products other than those expected by simple oligomerization are present, likely formed by double-bond isomerization catalyzed at acid sites. Additionally, both of the aluminosilicate materials catalyzed cracking reactions, forming non-C3n products. The reduced acidity of the zincosilicates relative to the aluminosilicates likely accounts for higher C3n product selectivity of the zincosilicates. Zincosilicates also exhibited higher linear-to-branched hexene isomer ratios (typically 1.0–1.5) when compared with the aluminosilicates, which had ratios on the order of 0.3. The mesoporous zincosilicate shows the best reaction behavior (including C3n product selectivity: ∼99% at both temperatures for Ni–Zn-MCM-41) of the catalytic materials tested here.

Transition-metal-free synthesis of imidazo[2,1-b]thiazoles and thiazolo[3,2-a]benzimidazoles via an S-propargylation/5-exo-dig cyclization/isomerization sequence using propargyl tosylates as substrates.

A transition-metal-free route for the synthesis of several N-fused heterocycles, including thiazolo[3,2-a]benzimidazoles and imidazo[2,1-b]thiazoles, is reported. The reaction between propargyl tosylates and 2-mercaptobenzimidazoles under basic conditions results in 3-substituted thiazolo[3,2-a]benzimidazoles, in yields up to 92% in a single synthesis step. With 2-mercaptoimidazoles as the substrate, the corresponding imidazo[2,1-b]thiazoles were exclusively obtained. The transformation is considered to proceed as an intermolecular S-propargylation that is followed by 5-exo-dig ring closure and double-bond isomerization.

Isomerization of 1-decene: Estimation of thermodynamic properties, equilibrium composition calculation and experimental validation using a Rh-BIPHEPHOS catalyst

The Rh-BIPHEPHOS catalyzed double bond isomerization of 1-decene as representative substrate for the hydroformylation of long-chain olefins was investigated. To obtain information about the thermodynamic equilibrium between the possible isomers of 1-decene, including all individual cis/trans isomers, calculations based on Gibbs energy minimization were performed and experimentally validated. The necessary thermodynamic properties of formation were calculated using Benson’s group increment theory (BGIT) method. Kinetic validation experiments were performed with 1-decene in two different solvents (DMF, toluene) to evaluate solvent polarity effects on the concentration courses. The experimentally determined equilibrium isomer composition was in very good agreement with the predictions. Thus, reaction isomerization equilibrium constants can be predicted reliably based on the applied method and can be used in subsequent kinetic investigations.

2,3-Dihalo-1-propenes as building blocks in Cu(I)-catalyzed domino reactions: efficient and selective synthesis of furans.

The Cu(I)-catalyzed reaction of 2,3-dibromo-1-propenes with β-ketoesters and 1,3-diketones, respectively, in DMF at 120 °C using Cs2CO3 as a base and hydroquinone as an additive exclusively delivers 2,3,5-trisubstituted furans and related compounds with yields up to 96%. The highly regioselective domino process is based on an intermolecular C-allylation followed by an intramolecular Ullmann type O-vinylation and a double bond isomerization.

Asymmetric Evans syn‐Aldol Reactions of Terpene‐Derived Enals: Scope and Limitations

AbstractThe (E)‐ and (Z)‐terpene‐based aldehydes 6b and 6c with a silyl ether function in the γ‐position were prepared and investigated in boron‐mediated asymmetric Evans aldol reactions. Screening experiments of chiral N‐acylated oxazolidinones 7, which are conveniently accessible from 5‐methyl‐5‐hexenoic acid and Evans oxazolidinone auxiliaries, with various boron triflates and terpenoid neral (Z)‐6a as aldehyde component, provided conditions in which highly selective formation of syn‐aldol adduct 5a occurred and competing C=C double bond isomerization to 10 was completely suppressed. Applying the optimized conditions to O‐silylated aldehydes 6b and 6c and N‐acyloxazolidinone derivative (R)‐7a confirmed the syn‐selectivity and gave the appropriate products syn‐5b,c and syn‐21b,c in good yields. In the case of neral‐derived syn adduct 5a, the configuration of the new stereogenic centers C‐2/C‐3 could be assigned as (2R,3S).

Synthesis of α-silylmethyl-α,β-unsaturated imines by the rhodium-catalyzed silylimination of primary-alkyl-substituted terminal alkynes.

In contrast to our previous report on the rhodium-catalyzed reaction of terminal alkynes with equimolar amounts of hydrosilanes and isocyanides leading to (E)- or (Z)-β-silyl-α,β-unsaturated imines A, the addition of an excess molar amount of hydrosilanes relative to isocyanides in the reaction of primary-alkyl-substituted terminal alkynes results in the production of α-silylmethyl-α,β-unsaturated imines B. Various isocyanides bearing tert-butyl and 1-adamantyl groups gave B with good product selectivity. Z isomers were formed stereoselectively in many cases. Regarding the mechanism for this reaction, when the hydrosilane was added to the reaction mixture in two portions, unsaturated imines A were initially formed, which then underwent double-bond isomerization, probably catalyzed by a Rh-H species, to give B.

Alkylation of toluene with 1-hexene over macroreticular ion-exchange resins

The macroreticular acidic ion-exchange resins Amberlyst 35, Amberlyst 46 and Purolite CT 275 were investigated as catalysts for the alkylation of toluene with 1-hexene and simultaneous dimerization and isomerization of the olefin at 373K. After six hours of reaction, 1-hexene conversion was complete. At low toluene concentration double-bound isomerization of 1-hexene was the main reaction. As toluene concentration increased, double-bond isomerization decreased and toluene alkylation and olefin dimerization reactions increased. By using Purolite CT 275 resin and for an almost equimolar toluene to 1-hexene ratio, the selectivity to dimers was 22%, that of mono- and di-alkylated compounds were 42% and 3.5%, respectively, while that of double-bound isomerization was 32.5%. These reactions catalyzed by macroreticular ion-exchange resins of high acid capacity and degree of crosslinking can be useful to boost naphtha streams in the refining industry by reducing volatile compounds and aromatics of low boiling point.

Heterologous expression of lysergic acid and novel ergot alkaloids in Aspergillus fumigatus.

Different lineages of fungi produce distinct classes of ergot alkaloids. Lysergic acid-derived ergot alkaloids produced by fungi in the Clavicipitaceae are particularly important in agriculture and medicine. The pathway to lysergic acid is partly elucidated, but the gene encoding the enzyme that oxidizes the intermediate agroclavine is unknown. We investigated two candidate agroclavine oxidase genes from the fungus Epichloë festucae var. lolii × Epichloë typhina isolate Lp1 (henceforth referred to as Epichloë sp. Lp1), which produces lysergic acid-derived ergot alkaloids. Candidate genes easH and cloA were expressed in a mutant strain of the mold Aspergillus fumigatus, which typically produces a subclass of ergot alkaloids not derived from agroclavine or lysergic acid. Candidate genes were coexpressed with the Epichloë sp. Lp1 allele of easA, which encodes an enzyme that catalyzed the synthesis of agroclavine from an A. fumigatus intermediate; the agroclavine then served as the substrate for the candidate agroclavine oxidases. Strains expressing easA and cloA from Epichloë sp. Lp1 produced lysergic acid from agroclavine, a process requiring a cumulative six-electron oxidation and a double-bond isomerization. Strains that accumulated excess agroclavine (as a result of Epichloë sp. Lp1 easA expression in the absence of cloA) metabolized it into two novel ergot alkaloids for which provisional structures were proposed on the basis of mass spectra and precursor feeding studies. Our data indicate that CloA catalyzes multiple reactions to produce lysergic acid from agroclavine and that combining genes from different ergot alkaloid pathways provides an effective strategy to engineer important pathway molecules and novel ergot alkaloids.

Double Bond Isomerisation and Migration—New Playgrounds for Transition Metal‐Catalysis

Double Bond Isomerisation and Migration—New Playgrounds for Transition Metal‐Catalysis

Fatty acid alterations in oils and fats during heating and frying*

Oils and fats degrade during the frying process and many reactions with numerous fatty acid alteration products have been examined. The geometrical isomerisation of double bonds leads to the formation of trans fatty acids. At frying temperatures also conjugated double bond systems are detected. The reaction of oxygen with unsaturated fatty acids results in hydroperoxides, which immediately degrade in further radical reactions at frying temperature. A set of oxygenated fatty acids has been detected including epoxy‐, keto‐ and hydroxyl fatty acids. Another route leads to β‐scission at the carbonyl‐ or the alkyl side of the oxygen bearing carbon atom in the fatty acid chain. In this case short chain fatty acids, aldehydic, keto, and hydroxyl acids appear together with volatile compounds. Also the formation of cyclic and furan fatty acids was detected. As a reaction between fatty acids also dimeric and polymerised fatty acids can be observed. Taking into account the different amounts of these fatty acid degradation products the physiological relevance has to be discussed. Due to high concentrations of dimeric and polymerised molecules these substances can lower significantly the digestibility of fried foods, while oxidised fatty acid monomers are readily absorbed and raise concern about their effect on lipid metabolism. These two different effects of altered TAGs and fatty acids have to be considered separately.

Solid-state NMR monitoring of a double bond isomerization in propene on ZnO

Monitoring of the 13C-label scrambling from the position 3 to the position 1 in the 13C-labeled propene adsorbed on zinc oxide has been performed with 1H and 13C solid state NMR in situ. This allowed us to characterize the dynamics of a double bond shift reaction in adsorbed propene, and derive the kinetic parameters of this reaction, which were not earlier available without using solid state NMR and 13C-labeling of the olefin.

A six-coordinated cationic ruthenium carbyne complex with liable pyridine ligands: synthesis, structure, catalytic investigation, and DFT study on initiation mechanism

A novel six-coordinated high-valence cationic ruthenium carbyne complex bearing two liable pyridine ligands was prepared in high yield by the reaction of the ruthenium-based complex (IMesH2)(Cl)2(C5H5N)2RuCHPh [IMesH2=1,3-dimesityl-4,5-dihydroimida-zol-2-ylidene] with excess iodine as an oxidant in CH2Cl2 at 25 °C under N2. The new ruthenium carbyne-based complex shows moderate to good catalytic activity for ring-closing metathesis reactions. Importantly, no double bond isomerization by-product was produced at elevated reaction temperatures (100 °C–137 °C) in the reaction catalyzed by the synthesized ruthenium carbyne complex. A mechanism involving the in situ conversion of the ruthenium carbyne through the addition of an iodide to the carbyne carbon was also proposed, and DFT calculations were performed to explain the initiating mechanism.

ChemInform Abstract: Intramolecular Fischer Indole Synthesis in Combination with Alkyne Hydroarylation: Synthesis of Tetracyclic Chromeno‐Indoles.

Aryl hydrazides bearing a carbonyl function connected through an alkyne tether underwent an intramolecular Fischer indolization and alkyne hydroarylation in a tandem fashion to afford novel tetracyclic chromeno-indoles. The accompanying isomerization of the 2H-chromene double bond can be avoided by stopping the tandem process at the indolophane stage and conducting the alkyne-hydroarylation reaction separately in the absence of a proton source.

ChemInform Abstract: Model Studies for a Ring‐Closing Metathesis Approach to the Bafilomycin Macrolactone Core from a 2,2‐Dimethoxy Tetraenic Ester Precursor.

A ring-closing metathesis strategy is reported for the construction of the 16-membered macrolactone core of the bafilomycins. One decisive key feature is the presence of a 2,2-dimethoxyketal functionality at C-2 that provides the required flexibility to the tetraenic ester precursor, allowing the ring-closing metathesis reaction to take place. Three different model esters of increasing complexity were successfully subjected to the 1,3-diene-ene ring-closing metathesis reaction. The best promoter for the simplest esters was the Grubbs first-generation precatalyst. A Hoveyda–Grubbs-type trifluoromethylamido-containing precatalyst developed by Mauduit's group gave satisfactory results for the most complex ester. In all experiments, the 12-Z-configured isomer was obtained as the major product. Subsequent microwave-promoted methanol elimination was achieved on the simplest model compound using camphorsulfonic acid (CSA) as a catalyst. Under these conditions, a E to Z isomerization of the double bond at C-4, as well as ca. 50 % isomerization of the 12-Z double bond into the corresponding 12-E isomer, were observed.

Isomerization of Δ5-androstene-3,17-dione into Δ4-androstene-3,17-dione catalyzed by human glutathione transferase A3-3: a computational study identifies a dual role for glutathione.

Glutathione transferases (GSTs) are important enzymes in the metabolism of electrophilic xenobiotic and endobiotic toxic compounds. In addition, human GST A3-3 also catalyzes the double bond isomerization of Δ5-androstene-3,17-dione (Δ(5)-AD) and Δ(5)-pregnene-3,20-dione (Δ(5)-PD), which are the immediate precursors of testosterone and progesterone. In fact, GST A3-3 is the most efficient human enzyme known to exist in the catalysis of these reactions. In this work, we have used density functional theory (DFT) calculations to propose a refined mechanism for the isomerization of Δ(5)-AD catalyzed by GST A3-3. In this mechanism the glutathione (GSH) thiol and Tyr9 catalyze the proton transfer from the Δ(5)-AD C4 atom to the Δ(5)-AD C6 atom, with a rate limiting activation energy of 15.8 kcal · mol(-1). GSH has a dual function, because it is also responsible for stabilizing the negative charge that is formed in the O3 atom of the enolate intermediate. The catalytic role of Tyr9 depends on significant conformational rearrangements of its side chain. Neither of these contributions to catalysis has been observed before. Residues Phe10, Leu111, Ala 208, and Ala 216 complete the list of the important catalytic residues. The mechanism detailed here is based on the GST A3-3:GSH:Δ(4)-AD crystal structure and is consistent with all available experimental data.

Kinetics of pi-complex isomerization during AlCl3 -catalyzed Friedel-Crafts reactions between linear olefins and p-xylene

Rapid isomerization of pi-complex intermediates results in the formation of multiple isomers of alkyl aromatics during AlCl3-catalyzed reactions between linear olefins and aromatic rings. The authors present results of a kinetic study of reactions between p-xylene, 1-dodecene, and linear tetradecenes. Product distributions are well predicted based on a model of reversible pi-complex isomerization. Surprisingly, no double bond isomerization was observed in the linear olefins: All isomerization occurred in the pi-complexes. Copyright © 2014 John Wiley & Sons, Ltd.

ChemInform Abstract: Sequential One‐Pot Method for Oxy‐Michael Addition, Heck Coupling, and Degradation Followed by Condensation: Facile Synthesis of 2‐Benzoxepin‐3(1H)‐ones.

Abstract A sequential one-pot intermolecular oxy-Michael addition, intermolecular Heck coupling, and intramolecular degradation (retro-oxy-Michael addition) followed by condensation method has been developed for the synthesis of interesting 2-benzoxepin-3(1H)-ones. Significantly, the 2-benzoxepin-3(1H)-ones form the core quantum of biologically vital natural products. The initial oxy-Michael addition and Heck coupling steps involve a straight forward construction of C–O and C–C bonds, whereas, the final condensation step follows a novel mechanistic path via intramolecular degradation, double bond isomerization, and intramolecular condensation. Notably, a remarkable solvent effect has been observed in-order to promote the final intramolecular condensation.