Olefinic Double Bond Research Articles

Mechanistic Insights into Carbonyl-Directed Rhodium-Catalyzed Hydroboration: ab Initio Study of a Cyclic γ,δ-Unsaturated Amide.

A two-point binding mechanism for the cationic rhodium(I)-catalyzed carbonyl-directed catalytic asymmetric hydroboration of a cyclic γ,δ-unsaturated amide is investigated using density functional theory. Geometry optimizations and harmonic frequency calculations for the model reaction are carried out using the basis set 6-31+G** for C, O, P, B, N, and H and LANL2DZ for Rh atoms. The Gibbs free energy of each species in THF solvent is obtained based on the single-point energy computed using the PCM model at the ECP28MWB/6-311+G(d,p) level plus the thermal correction to Gibbs free energy by deducting translational entropy contribution. The Rh-catalyzed reaction cycle involves the following sequence of events: (1) chelation of the cyclic γ,δ-unsaturated amide via alkene and carbonyl complexation in a model active catalytic species, [Rh(L2)2S2]+, (2) oxidative addition of pinacol borane (pinBH), (3) migratory insertion of the alkene double bond into Rh–H (preferred pathway) or Rh–B bond, (4) isomerization of the resulting intermediate, and finally, (5) reductive elimination to form the B–C or H–C bond with regeneration of the catalyst. Free energy profiles for potential pathways leading to the major γ-borylated product are computed and discussed in detail. The potential pathways considered include (1) pathways proceeding via migratory insertion into the Rh–H bond (pathways I, I-1, and I-2), (2) a potential pathway proceeding via migratory insertion into the Rh–B bond (pathway II), and two potential competing routes to a β-borylated byproduct (pathway III). The results find that the Rh–H migratory insertion pathway I-2, followed in sequence by an unanticipated isomerization via amide rotation and reductive elimination, is the most favorable reaction pathway. A secondary consequence of amide rotation is access to a competing β-hydride elimination pathway. The pathways computed in this study are supported by and help explain related experimental results.

Kinetic investigation of the effect of H2S in the hydrodesulfurization of FCC gasoline

The reactivity of different groups of olefins and S-compounds, as well as the inhibition effect of H2S on the reactivities of these groups were evaluated with a FCC gasoline over a CoMoS/γ-Al2O3 catalyst. The results demonstrated that the various degrees of steric hindrance around the double bond (CC) and of the thiophene molecules suppressed the hydrogenation (HYD) of olefins and hydrodesulfurization (HDS) of S-compounds, respectively. The inhibition effect of H2S caused by the easy adsorption of H2S on the catalyst sites was more severe on the HDS reactivity than that on the olefins HYD reactivity, thus leading to the decreased catalyst selectivity. The inhibition effect of H2S increased with the number of substituents to the olefin double bond and to the number of substituents to the thiophene molecules, which was inversely proportional to the adsorption constants of the olefin and thiophene molecules. Meanwhile, a modification of the HDS reaction pathway of thiophenes induced by H2S was also observed, and the HYD pathway was more depressed. The characterization by Fourier transformed infrared spectroscopy showed that the relative variations of the number of Lewis and Brønsted acid sites induced by the adsorbed H2S could explain the H2S effect.

Ph‐tetraMe‐Bithienine, the First Member of the Class of Chiral Heterophosphepines: Synthesis, Electronic and Steric Properties, Metal Complexes and Catalytic Activity

AbstractUnknown 1H‐2,7‐dihydro‐1‐phenylphosphepine, containing a 2,2′,5,5′‐tetramethyl‐3,3′‐bithiophene atropisomeric scaffold (Ph‐tetraMe‐Bithienine), and its oxide have been synthesized and structurally characterized by single‐crystal X‐ray diffraction analysis. The most evident structural feature is the very small dihedral angle. The electronic properties of the phosphane were quantitatively evaluated by cyclic voltammetry and compared with three other 2,7‐dihydro‐1‐phenylphosphepines differing in the nature of the biaromatic scaffold (biphenyl, 1,1′‐binaphthyl and 2,2′‐dimethoxybiphenyl). The racemate of the phosphane oxide was resolved into antipodes, which were reduced to the enantiopure phosphanes and employed as ligands in Rh and Pt complexes in homogeneous stereoselective catalytic reactions. The enantioselective ability and catalytic activity of the new mediators were found to be quite modest in the hydrogenation reactions of olefinic double bonds, whereas good performances were achieved in specific C–C bond‐forming reactions. The results are interpreted on the basis of the steric and electronic properties of the ligand.

Univalent Gallium Salts of Weakly Coordinating Anions: Effective Initiators/Catalysts for the Synthesis of Highly Reactive Polyisobutylene

The scope of the univalent gallium salts [Ga(C6H5F)2]+[Al(ORF)4]− and the new completely characterized [Ga(1,3,5-Me3C6H3)2]+[Al(ORF)4]− (RF = C(CF3)3) was investigated in terms of initiating or catalyzing the synthesis of highly reactive poly(2-methylpropylene)—highly reactive polyisobutylene (HR-PIB)—in several solvents. A series of polymerization reactions proved the high efficiency and quality of the univalent gallium salts for the polymerization of isobutylene. The best results were obtained using very low concentrations of [Ga(C6H5F)2]+[Al(ORF)4]− (down to 0.007 mol%) while working at reaction temperatures of up to ±0 °C and in the noncarcinogenic and non-water hazardous solvent toluene. Under these conditions, HR-PIB with an α-content of terminal olefinic double bonds up to 91 mol% and a molecular weight of 1000–2000 was obtained in good yields. Upon changing [Ga(C6H5F)2]+[Al(ORF)4]− for the electron richer [Ga(1,3,5-Me3C6H3)2]+[Al(ORF)4]−, polymerization temperatures could be increased to +10 °C. The reactivity of the gallium(I) cations therefore seems to be tunable through ligand exchange reactions. Experimental results, density functional theory calculations, and mass spectrometric investigations point toward a coordinative polymerization mechanism.

Photocatalytic oxidation of carbamazepine in triclinic-WO3 suspension: Role of alcohol and sulfate radicals in the degradation pathway

The photocatalytic oxidation of carbamazepine (CBZ, an antiepileptic drug frequently detected in surface water and WWTP effluent) in WO3 suspension under the irradiation of 420nm lamps has been investigated. The addition of S2O82− to this process can significantly accelerate the CBZ degradation. It was interesting to observe that conventional radical quenchers like methanol and ethanol promoted the photocatalytic oxidation of CBZ at low concentration (<100mM), while the tert-butanol inhibits or accelerates the CBZ degradation depending on its concentration. To explore this, the decomposition of CBZ with and without the presence of methanol was investigated in details through the comparison of evolution of intermediates/products, and the comparison of generated radicals by ESR spectroscopy in the process. Sulfate radicals are believed to play a major role during CBZ decay with the presence of methanol in this process. It was found the rate enhancement of methanol is likely due to the competition between quenching effect and cleaning effect on the catalyst surface. In addition, the reaction mechanism reveals that CBZ degradation is mainly dominant by the electrophilic attack of radicals at olefinic double bond in the central heterocyclic ring, leading to ring-opening and formation of various intermediates.

A single amino acid determines the catalytic efficiency of two alkenal double bond reductases produced by the liverwort Plagiochasma appendiculatum

Alkenal double bond reductases (DBRs) catalyze the NADPH-dependent reduction of the α,β-unsaturated double bond of many secondary metabolites. Two alkenal double bond reductase genes PaDBR1 and PaDBR2 were isolated from the liverwort species Plagiochasma appendiculatum. Recombinant PaDBR2 protein had a higher catalytic activity than PaDBR1 with respect to the reduction of the double bond present in hydroxycinnamyl aldehydes. The residue at position 56 appeared to be responsible for this difference in enzyme activity. The functionality of a C56 to Y56 mutation in PaDBR1 was similar to that of PaDBR2. Further site-directed mutagenesis and structural modeling suggested that the phenol ring stacking between this residue and the substrate was an important determinant of catalytic efficiency.

Effect of Br gassing after Ar plasma treatment of polyolefins

For simulation and acceleration of artificial polymer ageing, polyolefin foils were exposed to low-pressure Ar plasma. Plasma particle bombardment and irradiation induce C–C and C–H bond scissions by σ → σ ∗ excitations on the surface and in near-surface layers. Consequently, radicals are generated. They react by recombination, cross-linking, metastable trapping of the radical site or formation of olefinic double bonds. The long-living and metastable trapped C-radicals as well as double bonds in polyolefins were immediately exposed to bromine vapour without breaking the vacuum after switching-off the plasma. These reactive sites rapidly react with the molecular bromine under formation of C–Br bonds. For 5 min of argon plasma exposure, the elemental concentration of bromine was 13% for polyethylene and 22% Br/C for polypropylene as analysed by X-ray photoelectron spectroscopy. Nevertheless, not all C radical sites have reacted with bromine. Later on, when the polyolefins brought in contact with ambient air, an additional post-plasma reaction of the remaining trapped radicals with oxygen was observed. The oxygen concentrations were lower after bromine gassing, thus repressing partially the post-plasma oxidation in the analysed layer (ca. 6 nm) by radical quenching. Such bromination took place either at the surface or in near-surface layers because the Attenuated Total Reflectance (ATR)-FTIR spectra (sampling depth ca. 2500 nm) did not show significant changes for argon plasma-treated PE foils with and without bromine vapour exposure. Further addition of bromine may also occur on C=C double bonds.

Transformations of monoterpenoid ketones in supercritical isopropanol/CO2 in a continuous flow reactor in the presence of alumina. Competitive reduction of olefinic double bond and carbonyl group

Reactivity of monoterpenoid α,β-unsaturated ketones (carvone, verbenone and pinocarvone) in binary supercritical solvent isopropanol/CO2 in a flow reactor in the presence of granular Al2O3 was studied. Competitive reduction of olefinic double bond and carbonyl group was observed at the first reaction step. Subsequent transformation of intermediate products – alcohols – enables single step production of polyunsaturated monoterpenes 1,5,8-p-mentatriene and verbenene from carvone and verbenone, respectively, at contact times of several minutes.

ChemInform Abstract: Stereochemistry of the Olefinic Double Bond in 13‐Membered Heterocyclic Rings Accessible by Ring‐Closing Metathesis Reaction.

AbstractIn the presence of Grubbs I catalyst, the heterocyclic rings are either obtained as exclusive (E)‐isomers or as inseparable E/Z‐mixtures.

Biochemical characterization of an S-adenosyl-l-methionine-dependent methyltransferase (Rv0469) of Mycobacterium tuberculosis

Tuberculostearic acid (l0-methylstearic acid, TSA) is a major constituent of mycobacterial membrane phospholipids, and its biosynthesis involves the direct methylation of oleic acid esterified as a component of phospholipids. The methyltransferases of mycobacteria were long proposed to be involved in the synthesis of methyl-branched short-chain fatty acids, but direct experimental evidence is still lacking. In this study, we identified the methyltransferase encoded by umaA in Mycobacterium tuberculosis H37Rv as a novel S-adenosyl-l-methionine (SAM)-dependent methyltransferase capable of catalyzing the conversion of olefinic double bond of phospholipid-linked oleic acid to biologically essential TSA. Therefore, UmaA, catalyzing such modifications, offer a viable target for chemotherapeutic intervention.

Novel Synthetic Strategy for the Sulfonation of Polybutadiene and Styrene–Butadiene Copolymers

The selective and quantitative sulfonation of polybutadiene (PB) and triblock copolymers polystyrene-b-polybutadiene-b-polystyrene (SBS) has been successfully obtained through a novel procedure consisting of two reaction steps carried out in a single batch: free radical addition of thiolacetic acid to olefinic double bonds followed by autocatalytic oxidation of the thioacetylated polymer with in situ generated organic peracids. The polymers resulting from the two reactions were fully characterized by NMR, FTIR, and elemental analysis; the ion exchange capacity (IEC) of the sulfonated polymers was assessed by elemental analysis and titration with NaOH. Critical desulfonation temperatures of the poly(alkylsulfonate)s were observed in the range 160–270 °C, whereas the thermal decomposition starts at about 380 °C. The TUNA-AFM analysis of a sample of SBS containing 79 mol % of alkylsulfonic groups showed a phase-separated morphology consisting of polystyrene domains of about 28 nm embedded in the sulfonated p...

A phthalate family oxygenase reductase supports terpene alcohol oxidation by CYP238A1 from Pseudomonas putida KT2440

CYP238A1, one of the two P450 enzymes in the genome of Pseudomonas putida KT2440, has been produced heterologously in Escherichia coli, purified, and found to bind acyclic and cyclic terpene alcohols such as farnesol, nerolidol, linalool, and terpineol. The other P450 enzyme in this organism (gene locus: PP1950) was also produced in E. coli but no substrate has been identified from a limited screen. A phthalate family oxygenase reductase (PFOR) encoded by the PP1957 gene, just downstream of the PP1955 gene for CYP238A1, accepts electrons from the reduced form of both nicotinamide adenine dinucleotide (NADH) and nicotinamide adenine dinucleotide phosphate and is able to support monooxygenase activity of CYP238A1, both in vitro and in E. coli, in which both enzymes are produced. CYP238A1 oxidizes cis- and trans-nerolidol to the 9-hydroxy product, with no evidence of attack at the olefinic double bonds. The NADH turnover rate of 170 nmol(nmol-P450)⁻¹ Min⁻¹ for CYP238A1 with cis-nerolidol as substrate at a PP1957:CYP238A1 concentration ratio of 8:1 suggests that this PFOR could function as the physiological redox partner for CYP238A1. The physiological role of CYP238A1 may be related to the PP1955 gene being part of an island/cluster of inducible genes associated with energy metabolism and response to xenobiotics.

Structural understanding of solid-state photodimerization reactions of cinnamic amide derivatives in terms of reaction cavities – color developer for thermosensitive paper

The crystal structures of novel cinnamic amide derivatives, which are candidates for new color developers for thermosensitive paper, were investigated to reveal reactivity differences in solid-state photodimerization, in which one derivative was reactive, whereas the other was not. Unexpectedly, the traditional Schmidt's rule was not sufficient to explain the photoreactivity differences, and it was found that the partial reaction cavities around a specific region, and overlap of olefinic double bonds, were important factors in understanding the photoreactivity differences.

Synthesis of cis-Cinnamic Acid from trans-Cinnamaldehyde over Ag+-Exchanged Beta-Zeolite in Toluene

With a view to promoting green chemistry, cis-cinnamic acid (cis-CA) has been synthesized by using Ag-exchanged zeolites (AGZ). cis-CA [(Z)-3-phenyl-2-propenoic acid] and derivatives are physiologically active substances having plant growth regulatory activity, and have recently been isolated from plants[1,2]. Methods of synthesizing cis-CA reported up to now include photoisomerization of trans-cinnamic acid [the (E)-form, trans-CA], the method of reacting (Z)-2-bromostyrene with carbon monoxide in the presence of a palladium triphenylphosphine phasetransfer catalyst[3], and the method of electrolytic carboxylation of 2-bromostyrene using a nickel catalyst[4]. On the other hand, silver ion (Ag) -exchanged zeolite, silver ion supported on porous material[5] and complex membranes made up of amino acids and silver polymers[6] and the like have been utilized as olefin separation agents. In the present study, cis-CA was prepared in one pot synthesis using AGZ in toluene by novel methods of isomerization and oxidation of trans-cinnamaldehyde (TCA) to cis-CA exploiting the fact that Ag soft Lewis acid on AGZ forms a π -complex with the olefin double bond of TCA and reacts as the oxidant. (Scheme 1)

Computational study on mechanism of Rh(iii)-catalyzed oxidative Heck coupling of phenol carbamates with alkenes

A systematic theoretical study on the Rh-catalyzed oxidative Heck-coupling of phenol carbamates with alkenes is carried out. Two possible mechanisms (i.e. arene activation-first and alkene activation-first mechanisms) are examined. As to the C-H activation step, four mechanisms including oxidative addition, electrophilic substitution, concerted metallation-deprotonation (CMD), and σ-bond metathesis are evaluated. The calculation results indicate that the arene activation-first mechanism is more favorable for the overall catalytic cycle. This mechanism involves three steps: arene C-H activation at the position ortho to the carbamate directing group affording a six-membered rhodiacycle intermediate, insertion of the alkene double bond into the Rh(III)-aryl bond, and a final β-H elimination step to release the product and re-generate the catalyst. The rate determining step of the overall catalytic cycle is the arene C-H activation step, which is found to proceed through the acetate-assisted CMD mechanism.

Enantioselective Heck Arylations of Acyclic Alkenyl Alcohols Using a Redox-Relay Strategy

Progress in the development of asymmetric Heck couplings of arenes and acyclic olefins has been limited by a tenuous understanding of the factors that dictate selectivity in migratory insertion and β-hydride elimination. On the basis of key mechanistic insight recently garnered in the exploration of selective Heck reactions, we report here an enantioselective variant that delivers β-, γ-, or δ-aryl carbonyl products from acyclic alkenol substrates. The catalyst system imparts notable regioselectivity during migratory insertion and promotes the migration of the alkene's unsaturation toward the alcohol to ultimately form the ketone product. The reaction uses aryldiazonium salts as the arene source, yields enantiomeric products from opposite starting alkene configurations, and uses a readily accessible ligand. The racemic nature of the alkenol substrate does not bias the enantioselection.

Dibenzo[b,f]phosphepines: Novel Phosphane–Olefin Ligands for Transition Metals

New, stable heterobidentate phosphane–olefin ligands based on the dibenzo[b,f]phosphepine backbone are reported together with their redox properties and coordination chemistry to rhodium(I). The X-ray crystal structures and DFT calculations show different conformations for the P-phenyl (6a) and P-mesityl (6b) derivatives. Cyclic voltammetry (vs Fc/Fc+) of 6a supported by UV–vis spectroelectrochemistry showed two cathodic waves, a reversible one at E1/2 = −2.62 V (If/Ib = 1.0) and a quasi-reversible (If/Ib ≈ 1.2) one at E1/2 = −3.03 V. Reduction with sodium afforded a mixture of the radical anion [6a•]−, characterized by EPR spectroscopy, and dianion [6a]2–, for which an X-ray crystal structure was obtained. Both 6a and 6b bind to RhI centers, giving rise to 3:1 (8a) and 2:1 (8b) ligand:Rh complexes, respectively. Two dibenzo[b,f]phosphepines in 8a and 8b act as heterobidentate ligands in which both the phosphorus atom and the olefinic double bond coordinate to rhodium, but the third ligand in 8a binds as a monodentate P-donor. The cyclic voltammogram of 8b showed two close-lying waves, a one-electron reversible wave at −1.45 V and a two-electron quasi-reversible wave at −1.80 V (If/Ib ≈ 1.3). 8a showed a reversible wave at −1.71 V and irreversible waves at lower potentials.

5-[(Z)-2,3-Dimethoxybenzylidene]-1,2,4-triazolo[3,2-b][1,3]thiazol-6(5H)-one

The title compound, C13H11N3O3S, was synthesized from 1H-1,2,4-triazole-5-thiol in a one pot reaction. The fused thia­zolo[3,2-b][1,2,4]triazole system is essentially coplanar with the benzene ring: they enclose an inter­planar angle of 1.37 (13)°. The olefinic double bond is in a Z conformation. In the crystal, C—H⋯N hydrogen bonds link the mol­ecules into double layers parallel to the ab plane.

(2E)-3-(Dimethylamino)-1-(4-fluorophenyl)prop-2-en-1-one

In the title compound, C11H12FNO, the dihedral angle between the prop-2-en-1-one group and the benzene ring is 19.33 (6)°. The configuration of the keto group with respect to the olefinic double bond is s-cis. In the crystal, the mol­ecules form dimers through aromatic π–π stacking inter­actions [centroid–centroid distance = 3.667 (1) Å] and are linked via C—H⋯O inter­actions into chains along the b axis.

Ethyl 7-methyl-2-((1-methyl-1H-pyrrol-2-yl)methylene)-3-oxo-5-phenyl-3,5-dihydro-2H-thiazolo[3,2-a]pyrimidine-6-carboxylate

In the structure of the title compound, C22H21N3O3S, the thia­zole ring forms dihedral angles of 88.83 (7) and 9.39 (9)°, respectively, with the benzene and pyrrole rings. The dihydro­pyrimidine ring adopts a flattened boat conformation. The olefinic double bond is in a Z conformation.