Double Bond Isomerization Research Articles

Suppression of Undesirable Isomerization and Intermolecular Reactions of Double Bonds by a Linked Rotaxane Structure.

For luminescent materials, the isomerization and intermolecular reactions of their double bonds are often undesirable because they cause a reduction in the luminescence properties of the π-system. Herein, we report a new methodology to simultaneously prevent isomerization and intermolecular reactions by utilizing the steric effect of a linked rotaxane structure. The ring units are covalently linked in order to prevent any undesired shuttling effect from occurring during isomerization. In addition, the insulated structure provides robust optical properties by prevention of intermolecular reactions. Bulky linked rotaxane structures on both sides of the N=N and C=C double bonds suppress E/Z isomerization; photoluminescence quantum yield (PLQY) measurements reveal that this results in suppression of PLQY reduction caused by isomerization. Moreover, an improvement in the stability under light irradiation and air atmosphere is demonstrated.

Tandem Catalysts for Polyethylene Upcycling: A Simple Kinetic Model.

Of all plastics, the most abundantly produced is polyethylene, most of which is destined for landfills, shipping ports, and natural environments. The limited degradability and recyclability of this synthetic polymer motivates the development of chemical recycling methods. One possible approach consists of selective depolymerization to propylene with tandem olefin metathesis and double bond isomerization catalysts. In this paper, we transform thousands of coupled rate equations, pseudo-steady-state approximations, and local density approximations into one simple and analytically solvable Fokker-Planck type equation. The Fokker-Planck equation gives concise expressions for the rate of propylene production and polymer molecular weight evolution as functions of catalyst concentrations, rate constants, and ethylene concentrations.

A New Family of Rigid Dienone Musks Challenges the Perceptive Range of the Human Olfactory Receptor OR5AN1

A new family of dienone musks was discovered by alkylation of different aldehydes with but-3-en-1-yn-1-yllithium and subsequent domino reaction of a Saucy–Marbet transfer vinylation–Claisen rearrangement with an intramolecular Diels–Alder reaction, and concluding Lewis acid catalyzed double-bond isomerization. The newly synthesized dienone structures possess pleasant musk odors displaying fatty, slightly fruity and green facets. Although the dienone musks were predicted in silico to bind to the OR5AN1 receptor based on QM/MM calculations, they were found to be inactive in the in vitro assay. The latter results suggest that the OR5AN1 receptor is not the prime musk receptor but primarily responsible for the animalic character of certain macrocyclic ketones and nitro musks.

Antioxidant and anti-isomerization effects of sesamol and resveratrol on high oleic acid peanut oil

In the present study, the protective effects of sesamol and resveratrol on high oleic acid peanut oil were investigated. Different amounts of sesamol, resveratrol, and their combinations were added to the high oleic acid peanut oil to investigate the antioxidant effect and anti-isomerization effect to prevent cis to trans isomerization of double bonds. Rancimat results showed that the oil had the longest oxidation inducing time after adding 0.08% sesamol or 0.06% resveratrol (v/v). Thermogravimetric analysis suggested that when sesamol and resveratrol were added at 0.08% and 0.04% (v/v), the oxidation decomposition temperature was the highest. Schaal oven experiments indicated that the addition of sesamol and resveratrol could significantly reduce the peroxide content of high oleic acid peanut oil. The total fatty acid content in the oil samples increased significantly after high temperature treatment at 180 °C or 240 °C, and three new thermal isomerization trans products were measured (C18:1-9t, C18:2-9c,12t, C18:2-9t,12c). Meanwhile, the addition of sesamol (0.08%, v/v) or resveratrol (0.06%, v/v) significantly reduced the content of unsaturated fatty acid. For high oleic acid peanut oil heated to 180 °C, sesamol and resveratrol showed a better inhibitory effect on the production of trans-oleic acid than when heating at 240 °C.

Visible Light-Catalyzed Cascade Radical Cyclization of N-Propargylindoles with Acyl Chlorides for the Synthesis of 2-Acyl-9H-pyrrolo[1,2-a]indoles.

A novel and convenient visible light-catalyzed tandem radical cyclization of N-propargylindoles with acyl chlorides for accessing 2-acyl-9H-pyrrolo[1,2-a]indoles is established. This transformation involves sequential addition of the acyl radical to the carbon-carbon triple bond, intramolecular cyclization with the 2-position of indole, and isomerization of the carbon-carbon double bond. The experimental results show that this reaction contains a radical pathway and a radical chain process is not the major pathway for the formation of products.

Solid-State Molecular Organometallic Catalysis in Gas/Solid Flow (Flow-SMOM) as Demonstrated by Efficient Room Temperature and Pressure 1-Butene Isomerization.

The use of solid–state molecular organometallic chemistry (SMOM–chem) to promote the efficient double bond isomerization of 1-butene to 2-butenes under flow–reactor conditions is reported. Single crystalline catalysts based upon the σ-alkane complexes [Rh(R2PCH2CH2PR2)(η2η2-NBA)][BArF4] (R = Cy, tBu; NBA = norbornane; ArF = 3,5-(CF3)2C6H3) are prepared by hydrogenation of a norbornadiene precursor. For the tBu-substituted system this results in the loss of long-range order, which can be re-established by addition of 1-butene to the material to form a mixture of [Rh(tBu2PCH2CH2PtBu2)(cis-2-butene)][BArF4] and [Rh(tBu2PCH2CH2PtBu2)(1-butene)][BArF4], in an order/disorder/order phase change. Deployment under flow-reactor conditions results in very different on-stream stabilities. With R = Cy rapid deactivation (3 h) to the butadiene complex occurs, [Rh(Cy2PCH2CH2PCy2)(butadiene)][BArF4], which can be reactivated by simple addition of H2. While the equivalent butadiene complex does not form with R = tBu at 298 K and on-stream conversion is retained up to 90 h, deactivation is suggested to occur via loss of crystallinity of the SMOM catalyst. Both systems operate under the industrially relevant conditions of an isobutene co-feed. cis:trans selectivites for 2-butene are biased in favor of cis for the tBu system and are more leveled for Cy.

Synthetic feasibility of oxygen-driven photoisomerizations of alkenes and polyenes.

This review describes O2-dependent photoreactions for possible routes to double-bond isomerizations. E,Z-isomerizations triggered by O2 and visible light are a new area of potential synthetic interest. The reaction involves the reversible addition of O2 to form a peroxy intermediate with oxygen evolution and partial regeneration of the compound as its isomer. Targeting of O2-dependent photoisomerizations also relates to a practical use of visible light, for example the improved light penetration depth for visible as opposed to UV photons in batch sensitized reactions. This review is intended to draw a link between visible-light formation of a peroxy intermediate and its dark degradation with O2 release for unsaturated compound isomerization. This review should be of interest both to photochemists and synthetic organic chemists, as it ties together mechanistic and synthetic work, drawing attention to an overlooked subject.

Four resonance structures elucidate double-bond isomerisation of a biological chromophore.

Photoinduced double-bond isomerisation of the chromophore of photoactive yellow protein (PYP) is highly sensitive to chromophore-protein interactions. On the basis of high-level ab initio calculations, we scrutinise the effect of hydrogen bonds on the photophysical and photochemical properties of the chromophore. We identify four resonance structures - two closed-shell and two biradicaloid - that elucidate the electronic structure of the ground and first excited states involved in the isomerisation process. Changing the relative energies of the resonance structures by hydrogen-bonding interactions tunes all photochemical properties of the chromophore in an interdependent manner. Our study sheds new light on the role of the chromophore electronic structure in tuning in photosensors and fluorescent proteins.

Microbial transformation of diosgenin to diosgenone by Wickerhamomyces anomalus JQ-1 obtained from Naxi traditional Jiu Qu

Diosgenone [(20S,22R,25R)-spirost-4-en-3-one, C27H40O3] has been considered as a potential therapeutic alternative remedy for malaria. An efficient and economical approach of microbial transformation with diosgenin to diosgenone by the yeast strain Wickerhamomyces anomalus JQ-1 from Naxi traditional Jiu Qu was developed in this study. Chromatographic analysis confirmed that 85% of 0.1 mM diosgenin was transformed to diosgenone within 72 h. This research demonstrates that diosgenin could be converted to diosgenone through two-step pathway including 3β-hydroxyl oxidation and double bond isomerization rather than through one-step pathway, which prompted a further inference that the oxidation activity in W. anomalus JQ-1 has the same function with the Oppenauer-type oxidation which can convert diosgenin into diosgenone. Gaining specific functional strains from traditional fermented products will be a potential direction and ethnobotanical researches could provide helps with discovery and utilization of microbial resources.

Practical synthesis of 3-(2-arylethylidene)isoindolin-1-ones (analogues of AKS-182) and 3-(2-arylethylidene)isobenzofuran-1(3H)-ones

A simple and practical method is reported for the synthesis of 3-(2-arylethylidene)isoindolin-1-ones and 3-(2-arylethylidene)isobenzofuran-1(3H)-ones, proceeding with good to excellent yields and (E:Z) selectivity. This methodology involves the sequential reduction-dehydration reaction of readily obtained 3-(2-oxo-2-arylethyl)isoindolin-1-ones and 3-(2-oxo-2-arylethyl)isobenzofuran-1(3H)-ones followed by a base-catalyzed double bond isomerization with K2CO3 in acetonitrile. The development of a concise synthesis of AKS-182 has been achieved using this methodology.

Reaction of Pentenes, Hexenes, and Heptenes with Phosphoric Acid

A temperature swing absorption process using phosphoric acid was proposed for the removal of olefins from cracked naphtha. Evaluation of this required information on the reaction of naphtha range olefins with phosphoric acid. Reactive absorption of olefins at 50 °C in 85% phosphoric acid (H3PO4) was studied. The olefins evaluated were 1-pentene, 2-methyl-1-butene, 2-methyl-2-butene, cyclopentene, 1-hexene, 2-methyl-1-pentene, cyclohexene, 1-heptene, 2-methyl-1-hexene, and 4-methylcyclohexene. All of the olefins formed alkyl phosphoric acid esters, with Cn olefins forming Cn-, C2n-, and sometimes C3n-alkyl phosphoric acid esters. Branching in the olefin affected alkyl phosphoric acid ester stability; ester bonds to the α-carbon were more stable. The acyclic C5-alkyl phosphoric acid esters were more water soluble than oil soluble, and as the chain length of the alkyl group increased, oil solubility increased. Cyclohexyl and methyl cyclohexyl phosphoric acid esters formed stable water–oil emulsions. Reaction rates were low, but double bond isomerization took place and proceeded stepwise, with alkyl phosphoric acid esters being intermediate products rather than reaction intermediates. Although it was found that temperature swing absorption using phosphoric acid would not result in a viable process, the study provided several insights about the intermediate products and phase behavior of phosphoric acid catalyzed olefin conversion.

Green light powered molecular state motor enabling eight-shaped unidirectional rotation

Molecular motors convert external energy into directional motions at the nano-scales. To date unidirectional circular rotations and linear motions have been realized but more complex directional trajectories remain unexplored on the molecular level. In this work we present a molecular motor powered by green light allowing to produce an eight-shaped geometry change during its unidirectional rotation around the central molecular axis. Motor motion proceeds in four different steps, which alternate between light powered double bond isomerizations and thermal hula-twist isomerizations. The result is a fixed sequence of populating four different isomers in a fully unidirectional trajectory possessing one crossing point. This motor system opens up unexplored avenues for the construction and mechanisms of molecular machines and will therefore not only significantly expand the toolbox of responsive molecular devices but also enable very different applications in the field of miniaturized technology than currently possible.

Construction of All-cis-substituted Cyclopropane and Total Synthesis of Avenaol

The first total synthesis of avenaol was achieved using a new robust strategy involving all-cis-substituted cyclopropane formation via an alkylidene cyclopropane. The keys to success for the total synthesis were (i) Rh-catalyzed intramolecular cyclopropanation of an allene; (ii) Ir-catalyzed stereoselective double-bond isomerization to form an all-cis cyclopropane; and (iii) differentiation of two hydroxymethyl groups via regioselective cyclization and oxidation of tetrahydropyran based on the reactivity of cyclopropyl group. This strategy effectively avoids cyclopropane ring opening and undesired formation of a cage structure. Additionally, the proposed structure of avenaol, especially unique all-cis-substituted cyclopropane was confirmed correct by this total synthesis.

Brønsted Base Catalyzed One‐Pot Synthesis of Stereodefined Six‐Member Carbocycles Featuring Transient Trienolates and a Key Intramolecular 1,6‐Addition

AbstractA catalyst‐driven one‐pot reaction sequence is developed for the enantio‐ and diastereoselective synthesis of tetrasubstituted cyclohexenes from simple unsaturated ketones or thioesters. The method involves a tertiary amine/squaramide‐catalyzed α‐selective addition of transiently generated trienolates to nitroolefins, subsequent base‐catalyzed double bond isomerization, and an intramolecular (vinylogous) 1,6‐addition reaction, a rare key carbocyclization step that proceeded with essentially perfect stereocontrol.

Brønsted Base Catalyzed One-Pot Synthesis of Stereodefined Six-Member Carbocycles Featuring Transient Trienolates and a Key Intramolecular 1,6-Addition.

A catalyst-driven one-pot reaction sequence is developed for the enantio- and diastereoselective synthesis of tetrasubstituted cyclohexenes from simple unsaturated ketones or thioesters. The method involves a tertiary amine/squaramide-catalyzed α-selective addition of transiently generated trienolates to nitroolefins, subsequent base-catalyzed double bond isomerization, and an intramolecular (vinylogous) 1,6-addition reaction, a rare key carbocyclization step that proceeded with essentially perfect stereocontrol.

Rationalizing chain microstructure in the polyα-olefins synthesized by cationic AlCl3/H2O catalytic system

In this study, three middle range α-olefin monomers including 1-hexene, 1-octene, and 1-decene were oligomerized using conventional AlCl3/H2O catalytic system. Molecular weight and microstructure of the oligomers were analyzed by GPC and 1HNMR, respectively. By 1HNMR spectra, both internal (CHR=CHR′ and CHR=CR′R′′) and external (CH2=CR′R′′) olefins containing di and tri-substituted C=C bonds were detected. After successful oligomerization, synthesized polyα-olefins underwent hydrogenation process using Pd(0)-Hal catalyst to yield synthetic oils of PHex, POct, and PDec, respectively and then completion of the hydrogenation was confirmed by 1HNMR spectroscopy. The microstructure of the synthesized oligomers was rationalized using the ratio under the peak of CH + CH2/CH3 hydrogens (S1/S2) in 1HNMR spectra and the degree of oligomerization obtained from Mn. According to the results, the best match between theoretical and real S1/S2 is obtained when considering double bond isomerization in the synthesized PAOs. By knowing PAO molecular weight, a relationship between monomer type and S1/S2 in the PAO homopolymers was detected. Our suggested methodology can be generalized to the unknown PAO homopolymers to unravel their monomer type by simple 1HNMR and GPC analyses.

Potential‐Energy Surface and Dynamics Simulation of THBDBA: An Annulated Tetraphenylethene Derivative Combining Aggregation‐Induced Emission and Switch Behavior

AbstractElectronic structure calculations and nonadiabatic dynamics simulations were carried out on the excited state decay mechanism of a typical aggregation‐induced emission (AIE)‐active molecule, 10,10′,11,11′‐tetrahydro‐5,5′‐bidibenzo[a,d][7]annulenylidene (THBDBA), which was experimentally found to be almost non‐emissive in THF solution but highly luminescent as an aggregate. At the MS‐CASPT2//CASSCF level, the decay path from S1 leads to a conical intersection (CI) seam with the ground state (S0) via a cyclization process of two neighboring phenyl groups. Nonadiabatic dynamics simulations of 367 surface hopping trajectories show that all the structures of hopping points resemble those of the S1/S0 CI seam with cyclized geometry. The final structures of trajectories hopping to S0 belong to either Franck‐Condon (FC) like structures (66.8 %) or cyclized conformers (33.2 %), which agrees well with the experimental result of 23 % cyclization product (Y. Cai et al. Chem. Sci., 2011, 2, 2029–2034). Our results also indicate that long‐time irradiation leads to a photostationary state where the open and cyclized forms interconvert photochemically. The preference for photocyclization over double bond isomerization is due to the rigidity of the dihydrofulvene rings. From the point of view of AIE, the calculations suggest that THBDBA follows our restricted access to a CI (RACI) model because the photocyclization requires large displacements of the phenyl rings. These displacements must be blocked in the aggregate phase, inhibiting the decay and leading to luminescence. Our study contributes to understand the AIE and switch behavior of THBDBA and will be useful to support the design of new molecules with these features.

Oleate hydratase from Staphylococcus aureus protects against palmitoleic acid, the major antimicrobial fatty acid produced by mammalian skin

Oleate hydratases (OhyAs) belong to a large family of bacterial proteins catalyzing the hydration or isomerization of double bonds in unsaturated fatty acids. A Staphylococcus aureus gene (Sa0102) is predicted to encode an OhyA. Here, we recombinantly expressed and purified SaOhyA and found that it forms a homodimer that requires FAD for activity. SaOhyA hydrates only unsaturated fatty acids containing cis-9 double bonds, but not fatty acids with trans-9 double bonds or cis double bonds at other positions. SaOhyA products were not detected in S. aureus phospholipids and were released into the growth medium. S. aureus does not synthesize unsaturated fatty acids, and the SaOhyA substrates are derived from infection sites. Palmitoleate (16:1(9Z)) is a major mammalian skin-produced antimicrobial fatty acid that protects against S. aureus infection, and we observed that it is an SaOhyA substrate and that its hydroxylated derivative is not antimicrobial. Treatment of S. aureus with 24 μm 16:1(9Z) immediately arrested growth, followed by growth resumption after a lag period of 2 h. The ΔohyA mutant strain did not recover from the 16:1(9Z) challenge, and increasing SaOhyA expression using a plasmid system prevented the initial growth arrest. Challenging S. aureus with sapienic acid (16:1(6Z)), an antimicrobial fatty acid produced only by human skin, arrested growth without recovery in WT, ΔohyA, and SaOhyA-overexpressing strains. We conclude that SaOhyA protects S. aureus from palmitoleic acid, the antimicrobial unsaturated fatty acid produced by most mammals, and that sapienic acid, uniquely produced by humans, counters the OhyA-dependent bacterial defense mechanism.

Additive-Free Isomerization of Allylic Alcohols to Ketones with a Cobalt PNP Pincer Catalyst.

Catalytic isomerization of allylic alcohols in ethanol as a green solvent was achieved by using air and moisture stable cobalt (II) complexes in the absence of any additives. Under mild conditions, the cobalt PNP pincer complex substituted with phenyl groups on the phosphorus atoms appeared to be the most active. High rates were obtained at 120 °C, even though the addition of one equivalent of base increases the speed of the reaction drastically. Although some evidence was obtained supporting a dehydrogenation-hydrogenation mechanism, it was proven that this is not the major mechanism. Instead, the cobalt hydride complex formed by dehydrogenation of ethanol is capable of double-bond isomerization through alkene insertion-elimination.

On the role of co-cations in nickel exchanged LTA zeolite for butene dimerization

Abstract Partially Ni2+ exchanged Li+, Mg2+, Ca2+ and Na+ LTA zeolites were investigated for 1-butene dimerization, all showing selectivities higher than 90% into n-octenes and methylheptene isomers. The presence of the co-cations influences the rate of 1-butene double bond isomerization, while the Ni concentration determines the rates of dimerization. With higher electronegativity of the co-cation, the relative rate of isomerization increased, increasing so the selectivity to branched dimers. The higher Sanderson electronegativity of Li+ and Mg2+, with respect to Na+, is hypothesized to better stabilize the π-allyl Ni-complex-intermediate during butene isomerization. In consequence, the selectivity of alkene dimerization on Ni-exchanged zeolites can be tailored by acid-base properties of the alkali and alkali-earth cations.