Olefinic Double Bond Research Articles

Methoxy-Substituted Stilbenes, Styrenes, and 1-Arylpropenes: Photophysical Properties and Photoadditions of Alcohols

The photochemistry of trans-stilbene and four methoxy-substituted stilbene derivatives has been investigated in a variety of solvents. The fluorescence of all five trans isomers was quenched by 2,2,2-trifluoroethanol (TFE). Upon irradiation of the five substrates in TFE, the products derived from photoaddition of the solvent were detected. Nuclear magnetic resonance spectroscopy of the products formed by irradiation in TFE-OD indicated that the proton and nucleophile are attached to two adjacent atoms of the original alkene double bond. Irradiation of the corresponding methoxy-substituted styrenes and trans-1-arylpropenes in TFE produced the analogous solvent adducts. The photoaddition of TFE proceeded with the general order of reactivity: styrenes > trans-1-arylpropenes > trans-stilbenes. Transient carbocation intermediates were observed following laser flash photolysis of the stilbenes in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The results are consistent with a mechanism that involves photoprotonation of the substrates by TFE or HFIP, followed by nucleophilic trapping of short-lived carbocation intermediates. Compared to the other stilbene derivatives, trans-3,5-dimethoxystilbene displayed a large quantum yield of fluorescence and a low quantum yield of trans-cis isomerization in polar organic solvents. The unique photophysical properties of trans-3,5-dimethoxystilbene are attributed to formation of a highly polarized charge-transfer excited state (mu(e) = 13.2 D).

Cycloadditions to Alkenyl[2.2]paracyclophanes

AbstractCycloadditions between the 4‐alkenyl[2.2]paracyclophanes 7, 16–21 and the dienophiles 10a–h have been studied. Whereas 10a, b, d, and g prefer Diels–Alder addition involving the olefinic double bond and one double bond of a cyclophane benzene ring, 10c, e, f, and h undergo other cycloadditions such as ene reaction (10c), [2+2] cycloaddition to the olefinic double bond (10e) and heterodiene addition to the vinyl substituent (10f, h). Several of the isolated cycloadducts (e.g. 24–26, 52) are valuable substrates for the preparation of annelated cyclophanes. The mechanisms of several of these cycloadditions are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Thiocarbonyl compounds as regulating reagent in the radical addition of tertiary amines with alkenes using photoelectron transfer conditions

The efficiency of the photoinduced radical addition of tertiary amines to olefinic double bonds is significantly enhanced and the stereoselectivity is influenced when thiocarbonyl compounds are added to the reaction mixture.

Rhodium catalyzed hydroformylation of β-isophorone: An unexpected result

The rhodium catalyzed hydroformylation of β-isophorone ( 1a) should afford, as only oxo-product, the aldehyde 4-formyl-3,5,5-trimethylcyclohexan-1-one ( 2a), an important intermediate for the preparation of δ-Damascone, a floral woody fragrance used for soaps, shampoos, foam baths, etc. Surprisingly, under the reaction conditions adopted by us, we obtained two isomeric aldehydes, namely the expected 2a, formed in a small amount, and the (3,3-dimethyl-5-oxo-cyclohexyl)acetaldehyde ( 5a), that resulted to be the preponderant oxo-product. The chemoselectivity of the reaction was strongly affected by the substrate isomerization to α-isophorone ( 3a) and by the extensive formation of the corresponding saturated ketone 4a, so lowering the efficiency of the whole process. However, by perfoming the hydroformylation on a β-isophorone derivative without the possibility of conjugation of the two double bonds, namely the ketal 7,9,9-trimethyl-1,4-dioxa-spiro[4.5]dec-7-ene ( 1b), the chemoselectivity of the reaction strongly increased and the amount of the hydrogenation product was rather low. In any case the predominant oxo-product was the acetaldehyde derivative 5b, while the aldehyde 2b, deriving from the attack of the formyl group on the less substituted carbon atom of the olefinic double bond, was produced in a very small amount.

Cleavage of alkenes by anodic oxidation

Oxidative cleavage of olefinic double bonds to carboxylic acids, aldehydes or ketones is one of the important reactions in organic synthesis. Ozonolysis is mostly applied for this purpose, however, high costs for safety precautions in technical scale conversions demand alternatives. For this purpose different electrochemical methods are investigated. In the direct oxidation of cyclohexene at a platinum or graphite anode no cleavage occurs, but substituted and rearranged products are obtained. At the boron doped diamond electrode (BDDE) aliphatic olefins with high oxidation potential are not converted. Electrochemical ozonolysis by oxidation of water to ozone at the lead dioxide electrode leads to carboxylic acids as cleavage products in high material yield but low current yield. Anodic bromo-formyloxylation followed by an anodic cleavage provides a two step conversion of cyclohexene to hexane-1,6-dial derivatives. Thereby anodic discharge of bromide in formic acid leads to (2-bromocyclohexyl)-formate, which is converted to cyclohexane-1,2-diol and the major part of potassium bromide is recovered for the next cycle. This electrochemical conversion appears to be an attractive alternative to chemical oxidations with oxygen and catalysts or with hydrogen peroxide. The diol is cleaved in high yield to hexane-1,6-dial or its acetal either directly or indirectly with periodate as mediator.

Selective hydrogen transfer reduction of ketones by recyclable ruthenium complex catalysts containing a ‘ROMP polymer-attached’ ligand

Various pyridine and 2,2′-bipyridyl ligands attached to the polymer chain end of ring-opened poly(norbornene) were prepared by living ring-opening metathesis polymerization (ROMP) using Mo(CHCMe 2Ph)( N-2,6- i Pr 2C 6H 3)(O t Bu) 2. The prepared pyridine and 2,2′-bipyridyl derivatives were examined for their use as ligands for catalytic hydrogen transfer reduction of cyclohexanone in the presence of Ru(acac) 3 (in toluene/ i PrOH in the presence of NaO i Pr, at 50 °C, acac: acetylacetonato). The catalytic activity increased upon addition of the above polymer as the ligand, and the prepared catalyst could be recovered by filtration as the precipitate, by pouring the reaction mixture into methanol. The recovered catalyst could be reused without decrease in the activity. Since the olefinic double bond in the ROMP polymer was not hydrogenated under these reaction conditions, exclusive reduction of carbonyl group in various ketones, such as acetophenone, 5-hexen-2-one, 2-allylhexanone could be achieved in this catalysis.

Cross-Metathesis: Efficient Preparation of Trialkyl-Substituted Isoprenoid Olefins as Key-Intermediates for Tocopherol Synthesis

A summary of the application of ruthenium catalyzed olefin cross-metathesis towards the synthesis of tocopherols (vitamin E) is given. This group of biologically important fat-soluble antioxidants is synthetically available by various routes, for which key-intermediates containing trialkyl-substituted olefinic double bonds can now be prepared efficiently. The results presented may be of interest for the area of syntheses of isoprenoid natural products in general.

Hydroformylation of long-chain alkenes with new supported aqueous phase catalysts

In this paper the development and investigation of a new type of immobilized catalyst for the hydroformylation of long-chain alkenes is presented. The catalyst system consisted of the well known metal complex carbonylhydrido-tris-( m-sulfo-triphenylphosphine)-rhodium which was immobilized on activated carbon treated at high temperature. As starting materials 1-hexene, 1-decene, 1-tetradecene, 2-hexene and 2,3-dimethyl-2-butene were used. For all linear α-olefins the same n/ iso ratio in the product of 2:1 was determined. The reaction rate decreased with increasing chain length and sterical hindrance of the alkene double bond. All hydroformylation experiments were performed in a stirred semi-batch reactor. Catalyst leaching turned out to be a function of solvent polarity. Using n-heptane as solvent the immobilized catalyst remained stable on the carrier. The activity of the immobilized catalyst decreased compared to the homogeneous catalyst system. Water content was identified to be one of the most significant parameters of the reaction rate. The simulation of experimental data was modelled by a semi-empirical rate law. Within the simulation the reaction scheme consisting of hydroformylation, isomerization and aldol reaction was simultaneously calculated. It was possible to determine the reaction orders of all components, rate constants and the activation energies of all reactions.

Studies On The Crosslinking Of Poly (Vinyl Alcohol)

This paper is concerned with the cross-linking of poly(vinyl alcohol) (PVA) using maleic acid as the cross-linker. The curative (maleic acid) dose and the curing temperature and time were varied between 2.5 and 60% (w/w), 120 and 160 °C and 30 and 120 min, respectively. From a thorough swelling study in both hot and cold water (percentage swelling, gel content, swelling ratio, etc-) the optimum curative dose and curing conditions have been evaluated. The molecular weight between the cross-links exhibited a sharp fall up to a maleic acid dose of 20% (w/w). A comparative evaluation of maleic acid cross-linked and heat-treated PVA films has been done. Better heat stability for maleic acid cross-linked PVA was observed from thermogravimetric analysis. A shift in glass transition temperature was observed for both heat-treated and maleic acid treated PVA compared with the virgin one. IR spectroscopic study indicated the presence of an ester linkage and an olefinic double bond in maleic acid treated and heat-treated PVA films, respectively. Maleic acid cross-linked PVA is quite stable in different polar and nonpolar solvents. A definite structural pattern has been observed in maleic acid cross-linked PVA films through scanning electron microscopy.

An investigation on changes in chemical properties of pure ethylene-propylene-diene rubber in aqueous acidic environments

The influence of two aqueous acidic environments on two types of pure ethylene-propylene-diene (EPDM) rubber (i.e., elastomer) thin films is studied. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results revealed the formation of several oxygenated species on the surface after exposure. Raman spectroscopy along with ATR-FTIR results confirmed the vulnerability of the olefinic double bonds (C C) of 5-ethylidene-2-norbornene (ENB) in acidic environments. In addition, the aggressive nature of 20% Cr(VI)/H 2SO 4 was also observed through an increase in oxygenated species formation on the surface of EPDM rubbers compared to 20% H 2SO 4 under identical conditions. Complex formation on the surface of EPDM samples exposed to 20% Cr(VI)/H 2SO 4 through reactions of carboxylic groups (generated due to EPDM degradation) with Cr(III) (formed due to reduction of Cr(VI)) was also evident in ATR-FTIR. Finally, all the oxygenated species combined to form crosslinking as observed by the increase in gel fraction with exposure time. Effect of molar mass on chemical changes was noticed as samples with higher molar masses were found to form relatively higher amount of gel upon exposure. However, no significant effect of long chain branching was noticed. On this basis, plausible surface degradation mechanisms are proposed.

Surface characterisation of ethylene–propylene–diene rubber upon exposure to aqueous acidic solution

Two types of pure ethylene propylene diene rubbers were exposed to two different acids for varying period of time. Surface characterisation was carried out using X-ray photoelectron spectroscopy (XPS). Two EPDM rubbers selected for this study were comparable in co-monomer compositions but significantly different with respect to molar mass and the presence of long chain branching. Both rubbers contained 5-ethylidene-2-norbornene (ENB) as diene. Solution cast films of pure EPDM samples were exposed in two different acidic solutions, viz. chromosulphuric (Cr (VI)/H 2SO 4) and sulphuric acid (H 2SO 4) (20%, v/v) at ambient temperature from 1 to 12 weeks. XPS analysis indicated that several oxygenated species were formed on the surface of both rubbers after exposure. It was postulated from the XPS analyses that both aqueous acidic solutions attacked the olefinic double bonds (C C) of ENB. Furthermore, 20% Cr (VI)/H 2SO 4 also attacked the allylic carbon–hydrogen (C H) bonds of ENB resulting in more oxygenated species on the surface compared to 20% H 2SO 4 under identical conditions. Cr (VI) in the 20% Cr (VI)/H 2SO 4 was found to play an important role in alteration of surface chemistry. Studies using a model system consisting of EPDM mixed with Cr (VI) and Cr (III) salts revealed that the change of oxidation state from Cr (VI) to Cr (III) as a consequence of direct involvement of Cr (VI) in the chemical alteration of EPDM surfaces. Interestingly, the presence of long chain branching and molar mass did not significantly influence the chemical processes owing to the acid treatment.

2′-Hydroxy-3′-(morpholin-4-yl-methyl)-4′,6′-dimethoxy-2-chloro-chalcone

In the title compound, C22H24ClNO5, the carbonyl group is in an s-cis configuration with respect to the olefinic double bond. In the crystal structure, there are weak π-stacking inter­actions but there are no significant inter­molecular hydrogen bonds.

One or More C:C Bond(s) by Elimination of S, Se, Te, N, P, As, Sb, Bi, Si, Ge, B, or Metal Functions

AbstractFor Abstract see ChemInform Abstract in Full Text.

Computational Mechanistic Studies on Enantioselective pybox−Ruthenium-Catalyzed Cyclopropanation Reactions

The mechanism of the ruthenium(II)-catalyzed cyclopropanation reaction of olefins with diazo compounds has been extensively investigated for a medium-sized reaction model by means of DFT calculations. The starting ethylene complex of the dichloro[(E)-2-(methylimino)-N-(1E,2E)-2-(methyliminoethylidene)ethanamine]ruthenium(II) catalyst undergoes a ligand exchange with methyl diazoacetate to yield a reaction intermediate, which subsequently undergoes nitrogen extrusion to generate a ruthenium−carbene complex. The cyclopropanation step takes place through a direct carbene addition of the ruthenium carbene species to the olefin double bond to yield a catalyst-product complex, which can finally regenerate the starting complex. Stereochemical considerations on a “real-world” systemthe cyclopropanation reaction of styrene with methyl diazoacetate, catalyzed by a chiral pybox−ruthenium complexhave been investigated by means of full quantum-mechanical calculations on this reaction. The theoretical results show exce...

Characterization of the Sulfhydryl-Sensitive Site in the Enzyme Responsible for Hydrolysis of 2- Arachidonoyl-Glycerol in Rat Cerebellar Membranes

We have previously reported that the endocannabinoid, 2-arachidonoyl-glycerol (2-AG), is hydrolyzed in rat cerebellar membranes by monoglyceride lipase (MGL)-like enzymatic activity. The present study shows that, like MGL, 2-AG-degrading enzymatic activity is sensitive to inhibition by sulfhydryl-specific reagents. Inhibition studies of this enzymatic activity by N-ethylmaleimide analogs revealed that analogs with bulky hydrophobic N-substitution were more potent inhibitors than hydrophilic or less bulky agents. Interestingly, the substrate analog N-arachidonylmaleimide was found to be the most potent inhibitor. A comparison model of MGL was constructed to get a view on the cysteine residues located near the binding site. These findings support our previous conclusion that the 2-AG-degrading enzymatic activity in rat cerebellar membranes corresponds to MGL or MGL-like enzyme and should facilitate further efforts to develop potent and more selective MGL inhibitors.

Effects of Structure on Radical-Scavenging Abilities and Antioxidative Activities of Tea Polyphenols: NMR Analytical Approach Using 1,1-Diphenyl-2-picrylhydrazyl Radicals

Tea (Camellia sinensis) leaves contain various antioxidants such as ascorbic acid (1) and polyphenols. This study tries to clarify the molecular mechanisms underlying the antioxidative and radical-scavenging activities of these antioxidants, and the reactivities of each antioxidant have been compared against that of the stable free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH, 2) using nuclear magnetic resonance (NMR) analysis. Catechol (3) and (+)-taxifolin (4) were oxidized to o-quinone by 2. However, ethyl protocatechuate (5) and quercetin (6) were not oxidized to o-quinone, even though they possess a catechol structure. The radical-scavenging ability of o-dihydroxyl phenolic compounds with a conjugated olefinic double bond (e.g., 6) was superior to that of compounds without this bond (e.g., 4), whereas the ability of o-dihydroxyl phenolic compounds possessing a conjugated carbonyl bond (5) was inferior to that of compounds lacking this bond (3). Vicinal trihydroxyl phenolic compounds with a conjugated olefinic double bond [e.g., myricetin (7)] had an inferior scavenging ability as compared with compounds lacking this bond [e.g., pyrogallol (8)], but 7 was a better scavenger than compounds with a conjugated carbonyl double bond [e.g., ethyl gallate (9)]. In addition, vicinal trihydroxyl phenolic compounds (e.g., 9) were superior to o-dihydroxyl phenolic compounds (e.g., 6). Finally, 1 scavenged radicals more quickly than 8.

Inter- and Intramolecular [2 + 2]-Photocycloaddition of Tetronates ? Stereoselectivity, Mechanism, Scope and Synthetic Applications.

For Abstract see ChemInform Abstract in Full Text.

The activation of C [dbnd]O bond in acetone by Cu + cations in zeolites: IR studies and quantum chemical DFT calculations

Our previous IR studies as well as quantum chemical DFT calculations evidenced that Cu + ions in zeolites were able to activate C C double bond in alkenes by π back donation of d electrons of Cu + to π * antibonding orbitals of alkenes. It resulted in a distinct weakening of C C bond. The present study was undertaken in order to answer the question if Cu + ions in zeolites were also able to activate another than C C double bond. We studied therefore the interaction of acetone with Cu + in zeolites CuZSM-5, CuMCM-41, CuX and CuY. IR studies showed a weakening of C O bond and a red shift of IR band by 39–51 cm −1. The experiments in which the small doses of acetone were adsorbed as well as desorption studies evidenced that Cu + bonded acetone more strongly than other adsorption sites, such as hydroxyl groups. DFT modeling of the adsorption of the acetone molecule on copper site gave the information about the function of the zeolite as a host for transition metal cationic sites and as an electron reservoir. Calculated values of electron affinity and HOMO energy allowed to explain that, on the basis of the charge distribution analysis, electrons flowed from the acetone molecule to the copper site, so that the molecule was positive. It was evidenced by the analysis of the charge distribution. Therefore, the activation upon adsorption has been justified by the electronic structure of the molecule, its electron affinity as well as the ability of the site to π back donation. Moreover, the calculated value of the red shift of the IR band of the activated C O bond was similar as experimental one.

Evidence for formation and different evolution of tertiary rhodium alkyl intermediates under rhodium-catalyzed deuterio-(hydro)formylation of 1-( n-pyridyl)-1-phenylethenes

Deuterioformylation of the vinylidenic substrates 1-( n-pyridyl)-1-phenylethenes, in the presence of phosphine modified Rh 4(CO) 12 as catalyst precursor, was carried out at 100 atm of CO and D 2 (1:1), 80 °C and at partial and complete substrate conversion. The direct 2H NMR analysis of the crude reaction mixture led to the conclusion that, under these conditions, the branched alkyl rhodium intermediate is formed almost exclusively. It can: (i) β-eliminate, (ii) undergo migratory insertion on CO or (iii) oxidative addition of deuterium to various extents depending on the position of the nitrogen atom with respect to the olefinic double bond, thus accounting for the observed different chemo- and regioselectivities.

Co2(CO)8 as Novel and Water-tolerant Reagent for the Conversion of Azides to Amines in Aqueous Media

Abstract Azides are readily converted into their corresponding amines using a catalytic amount of Co2(CO)8 under mild conditions. The method is highly chemoselective and compatible with a variety of functionalities such as halides, esters, acids, ethers, nitro, cyano and olefinic double bonds present in the molecule.