Conjugated Double Bonds Research Articles

Reduction of conjugate double bonds with trichlorosilane

A variety of α,β-unsaturated esters and cyclic ketones underwent smooth reduction of the carbon–carbon double bond with a combination of inexpensive and readily available trichlorosilane and CoCl2. The reactions are performed under very mild conditions and products are obtained in high yields.Key words: reduction, carbonyl compounds, trichlorosilane, ketones, chemoselectivity.

Enantiodivergent syntheses of cycloheptenone intermediates for guaiane sesquiterpenes

The syntheses of enantiomeric 6-isopropenyl-3-methyl-2-cycloheptenones 16 and 22 have been effected starting from ( R)-(−)-carvone. In the synthesis of 16, ( R)-(−)-carvone was reduced and the resulting dihydrocarvone transformed regioselectively into silyl enol ethers. Cyclopropanation with dibromocarbene and in situ rearrangement gave an α-bromo-cycloheptenone which was reduced to the ( R)-(+)-cycloheptenone 16. In the synthesis of 22, ( R)-(−)-carvone was cyclopropanated with a sulfur ylide, followed by reduction with LiAlH 4 and acid-catalyzed cyclopropylcarbinyl rearrangement to afford a cycloheptenol. Oxidation and double bond conjugation led to the ( S)-(−)-cycloheptenone 22 in a partially racemized form. Four cycloheptenones have been obtained and are suitable intermediates for the enantiodivergent syntheses of guaiane sesquiterpenes.

Oligomerization of early transition metal [M(OH)3]2(mu-C2) acetylides toward the formation of [(OH)3MC]n (n = 4, 6) metalla carbides: a theoretical study by density functional theory.

Density functional calculations were performed on a series of M(OH3)-substituted (M = Ti,V) cyclopolyenes as simple models is metal carbides. We studied the oligomerization of the metal acetylide complexes [MLn]2 (mu-C2) as a possible precursor of these [(OH)3MC]n (n = 4,6) hypothetical species. Special emphasis was placed on the comparison of the main properties of these metal substituted cyclopolyenes with those of the corresponding cyclopolyenes in an attempt to study the effects of the metal substituents on the organic C4 and C6 cyclic moieties. Whereas for the titanium species, the pi system of the polyene moiety is slightly perturbed, the electronic structures and molecular geometries found for the vanadium species suggest a metalla radialene nature for these compounds, with the endocyclic conjugation of carbon-carbon double bonds replaced by an exocyclic arrangement of carbon-metal double bonds.

Reduction of conjugate double bonds with trichlorosilane

A variety of α,β-unsaturated esters and cyclic ketones underwent smooth reduction of the carbon–carbon double bond with a combination of inexpensive and readily available trichlorosilane and CoCl2. The reactions are performed under very mild conditions and products are obtained in high yields.Key words: reduction, carbonyl compounds, trichlorosilane, ketones, chemoselectivity.

Stereoselective Synthesis of Highly Substituted Piperidines

Enantiopure piperidines 4 may be accessed in very good overall yields and high stereoselectivity from the bifunctional products 2 of the silyloxy Cope rearrangement of chiral aldol products 1 by sequential nucleophilic addition of primary amines and subsequent hydrogenation. The reaction is proposed to proceed by initial imine formation followed by an intramolecular aza-conjugate addition to the α,β-unsaturated imide. The stereoselectivity is controlled by A(1.2) strain between the imine N-alkyl group and the conjugate double bond. In an alternate approach, polyalkyl-substituted piperidines were prepared by the addition of organozinc reagents to cyanopiperidines readily obtained from the Cope products in the presence of a silver salt.

NEXAFS studies of adsorption of benzene on Si(100)-2×1

Benzene adsorption on Si(100)-(2×1) is investigated at 100 and 300 K by vibrational infrared (IR) spectroscopy, thermal desorption and near-edge X-ray absorption fine structure (NEXAFS) studies. At cryogenic temperatures (100 K), benzene is found to be predominantly physisorbed on this surface, whereas at room temperature benzene chemisorbs on Si(100)-2×1. IR studies show vibrational features at 2945 and 3044 cm −1 corresponding to sp 3 and sp 2 C–H stretching modes, respectively, and NEXAFS indicates the absence of conjugated double bonds in chemisorbed benzene. Two possible chemisorption structures are indicated, consistent with previous studies of this system. The majority structure is consistent with Diels–Alder type addition of benzene to the dimer of the Si(100)-2×1 surface and is described as 1,4-cyclohexadiene-like. The presence of another structure of chemisorbed benzene is suggested by a splitting in the π* transitions in the NEXAFS spectra of chemisorbed benzene. The energy difference is inconsistent with conjugation of double bonds, and the two features have different angular dependencies. The angular dependence for both π* transitions was studied and gave an angle between the double bond and the silicon surface of ∼30° for the primary 1,4-cyclohexadiene-like adduct and ∼43° for the second structure.

Efficient Preparation of Functionalized (E,Z) Dienes Using Acetylene as the Building Block

Efficient Preparation of Functionalized (<i>E,Z</i>) Dienes Using Acetylene as the Building Block

Catalytic Hydrogen Transfer Reductions Using Ammonium Formate. A Review

An account of recent developments on selective reduction of several important functional groups by catalytic transfer hydrogenation using ammonium formate and palladium or nickel is presented. This includes reduction of nitro alcohols, α,β-unsaturated nitroalkenes, quinoline and isoquinoline, carbonyl functionalities, carbon-carbon double bond in conjugation to carbonyl, sulfonyl and phosphonate moieties, and epoxides. Deoxygenation of heteroaromatic N-oxides and deprotection of 1,3-dibenzyluracils have also been addressed.

Analysis of Molecular Species of Triacylglycerols from Vegetable Oils Containing Fatty Acids with Non-Methylene-Interrupted Double Bonds, by HPLC in the Silver-ion Mode

The possibilities for application of silver ion HPLC to analysis of the triacylglycerols containing conjugate trienoic acids and Δ5-polymethylene-interrupted acids and proportions of triacylglycerol fractions obtained by silver-ion HPLC from the seed oil of Momordica charantia double bonds were examined, respectively. The triacylglycerols of seed oils containing conjugate trienoic acids such as α-eleostearic acid (C18 : 3 9c, 11t, 13t) and punicic acid (C18 : 3 9c, 11t, 13c) were resolved by silver-ion HPLC. Fractions were fractionated on the basis of the number and configuration of double bonds in the species, and the elution profile is quite different from that of the species comprising exclusively saturated and unsaturated fatty acids with methylene-interrupted double bonds; for instance, the species (DTc2) composed of one dienoic acid and two conjugate trienoic acids eluted much earlier than the species (D2Tc) composed of two dienoic acids and one conjugate trienoic acid, in spite of having larger number of double bonds. This means that the interaction of conjugate double bonds with silver ions is weaker than that of methylene-interrupted double bonds, presumably because of the delocalization of π-electrons in conjugate double bonds. In this instance, the strength of interaction of a conjugate trienoic double bond system with silver ions seemed to be between that of methylene-interrupted dienoic and monoenoic double bond systems. Triacylglycerols of the seeds of Ginkgo biloba have been resolved by HPLC in the silver-ion mode according to the number and position of double bonds. In this instance, the strength of interaction between the π-electrons of double bonds in the fatty acyl residues and silver ions is in the order; C18 : 3ω3>C20 : 3Δ5, 11, 14C18 : 3Δ5, 9, 12>C18 : 2ω6>C18 : 2Δ5, 9>C18 : 1ω9>C18 : 1ω7.

SYNTHESIS OF SUBSTRATE ANALOGUES AND INHIBITORS FOR THE PHOSPHOGLYCERATE MUTASE ENZYME

Several substrate analogues of the title enzyme were synthesized as well as with possible irreversible inhibitors, analogues of phosphoglycolate, the cofactor for this enzyme. The main routes involved an Arbuzov type reaction on functionalized halides, a reaction significantly improved by a sonication procedure and reaction of the diethylphosphite anion on tosylates. epoxides were obtained by quantitative oxidation of conjugate double bonds using DMDO. Preliminary assays indicated a promising activity in some of these compounds. Symbols: EM: phosphoglycerate mutase, 1,3-diPGA: 1,3-diphosphoglycerate, 2-PGA: 2-phosphoglycerate, 3-PGA: 3-phosphoglycerate, 2,3-diPGA: 2.3-diphosphoglycerate, PG: phosphoglycolate, DMDO: dimethyldioxirane, m-CPBA: meta-chloroperbenzoic acid

Carotenoids and related polyenes. Part 4.1 Synthesis of carotenoid analogues containing a conjugated carbonyl group and their fluorescence properties

Fluorescence properties of several synthetic carotenoid analogues have been investigated in order to assess the relationship between molecular structures and function as a photosynthetic antenna. The origin of fluorescence is determined by two factors; the length of the conjugated double bond system and the presence of a carbonyl group. For efficient energy transfer to chlorophyll a, eight conjugated double bonds and an associated carbonyl group are required, which ensures that fluorescence occurs from the S1 state.

ChemInform Abstract: Magnesium in Methanol Selective Reduction of a Conjugate Double Bond in an α,β‐Unsaturated Ester Related to Pregnadiene.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Four-wave-mixing interferometer

We have developed a new method of determining in time both the real and the imaginary parts of third-order nonlinear-optical coefficients. In this method the phase-conjugated four-wave-mixing signal beam interferes with one of the transmitted pump beams. By comparing the interference pattern with that of a known reference, we are able to determine the real and the imaginary parts of the third-order optical nonlinearity for an unknown sample. The real and the imaginary parts can also be separated when one incoming beam is delayed. We apply this method to a bis-thienyl polyene molecule containing five conjugate double bonds and find that the hyperpolarizability is (gamma1111) = (-2.5 - 0.17i) x 10(-30) esu.

Magnesium in Methanol Selective Reduction of a Conjugate Double Bond in an α,β-Unsaturated Ester Related to Pregnadiene

Magnesium in Methanol Selective Reduction of a Conjugate Double Bond in an α,β-Unsaturated Ester Related to Pregnadiene

Diastereoselective synthesis of ethyl ( Z)-3-(8-methylimidazo-[1,2- a]pyrid-2-yl)-2-phenylthioacrylate. X-ray crystal structure and conformational analysis

The title compound 2, a gem vinyl sulfide ester, has been obtained diastereoselectively (de > 98%) by action of the ethyl thiophenoxyacetate carbanion on the imidazo[1,2- a]pyridinecarbaldehyde 1 in a basic medium, at low temperature. The X-ray crystal structure of 2 (C 19H 19N 2O 2S: M r = 338.43, triclinic, P 1 ̄ , a = 8.193(3) A ̊ , b = 10.090(2) A ̊ , c = 10.981(4) A ̊ , α = 88.12(2)°, β = 78.66(4)°, γ = 78.53(2)°, V = 872.3(6) A ̊ 3 , Z = 2, D calc = 1.29 g cm −3, λ( Mo Kα) = 0.71069 A ̊ , μ = 0.189 mm −1, F(000) = 356, T = 293 K, R = 0.043 for 3610 observed reflections) has been determined and confirmed the Z configuration. The molecule is almost planar except for the phenyl ring situated in an approximate perpendicular plane. Despite the presence of the conjugate double bonds of the vinyl ester group (acrylate), coplanar with the imidazopyridine heterocycle, there is no evidence of π-electron delocalization over the whole structure. The crystal cohesion is ensured by a dense network of van der Waals contacts. A conformational analysis of the Z and E isomers by means of a Monte Carlo search and a stochastic dynamics simulation in CHCl 3 has shown that according to the method the Z isomer is more stable than the E isomer by about 7 to 10 kJ mol −1.

Structure and properties of polymers modified by ion implantation

Thin films of oriented polyethylene (PE), polypropylene (PP), polytetrafluoroethylene (PTFE) and polyamide (PA6) were modified by the implantation of 150 keV Sb + ions to the fluences 10 12–10 15 cm −2. The Sb depth profiles were determined by a standard Rutherford back-scattering technique and the range parameters were found to differ from the theoretical TRIM estimate. The thickness of the ion beam modified surface layer is about 150 nm for all polymers examined. Production of conjugate double bonds and polymer surface oxidation were proved by means of i.r. and u.v. spectroscopies. Surface polarity, obtained by goniometric measurements, is an increasing function of the implanted dose with only the exception of PA6 where a polarity decrease is observed. The measured temperature dependence of the sheet resistivity for PE, PP and PA6 do not correspond to the well known variable range hopping mechanism.

エキシマレーザーと生体脂肪

Effects of ultraviolet laser irradiation on biological lipid have been studied for the medical application. A suet has been adapted as a biological lipid. Drilling depths of a suet for ArF, KrF and XeCI excimer lasers have been measured. Drilling ability for KrF excimer laser was remarkably better than that for other lasers. In addition, drilling without thermal disturbance was found in the low repetitive irradiation, suggesting that the dominant process on the drilling was the photochemical effect. In ArF excimer laser irradiation, the thermal damage zone was created by the thermal effect due to the nonradiative transition. Denaturation of a suet after excimer laser irradiation is examined from the ultraviolet absorption spectra. The absorption owing to the conjugate double bond in a suet was influenced by ArF and KrF laser irradiations.

Oxidation state of germanium promoter on a palladium/ carbon catalyst and its role in hydrogenation reactions

The oxidation state and location of germanium promoter in a carbon-supported palladium catalyst were studied by X-ray photoelectron spectroscopic, X-ray diffraction, electrochemical and atomic emission spectroscopic methods. During promotion with an aqueous GeO 2 solution at room temperature, germanium deposited exclusively on palladium particles via the ionization of adsorbed hydrogen. Two types of germanium species were identified. Up to a Ge/Pd 8 = 0.6 atomic ratio only strongly bound adatoms with a partial positive charge (Ge n+ ) were formed. At higher promoter/palladium ratios a rapid bulk alloy formation was also observed (weakly bound species, Ge 0). The rate of bulk alloy formation was dependent on the particle size of palladium and on the initial Ge/Pd ratio. Measurement of the open circuit potential of the catalyst slurry revealed that the increase in the oxidation state of germanium during hydrogenation reactions was negligible. Germanium deposition onto palladium suppressed the hydrogen adsorption and absorption. Accordingly, the activity of the bimetallic catalysts decreased with increasing promoter/palladium ratio in the liquid phase hydrogenation of organic substrates having various reducible functional groups. An anomalous increase in activity and a substantial change in selectivity was observed in the hydrogenation of C=C double bonds conjugated with hydroxyl, carbonyl or phenyl groups, while this phenomenon was absent in the reduction of substrates having a C=C double bond in conjugation with carboxyl, nitrile or ester functional groups. The role of Ge n+ acidic centers could be excluded and an ensemble effect of Ge adatoms resulting in changes in the adsorption of substrates and/or products was suggested.

Molecular orbital studies on the model compounds of doped polyacetylene

The electronic structures of model compounds of doped polyacetylene are investigated by the molecular orbital method. The structures of charge transfer complexes between short polymethine with Na or Cl atoms are optimized by the ab initio HF SCF MO calculation. It is found that the allyl group in the polymethine chain acts as a bidentate ligand to the dopant and it forms a stable closed shell unit which shields the conjugation of double bonds. The polyene with such units at the trans position is assigned to the charged soliton-antisoliton. The polymethine chain which consists of two coordinated allyl groups and a short radical chain between them is called the polson. These structures are used in the calculation of the energy levels of doped long chains by the P-P-P method. The mid gap state is found with the charged soliton lattice and the metallic state is obtained with the polson lattice.

All- trans retinal constitutes the functional chromophore in Chlamydomonas rhodopsin

Orientation of the green alga Chlamydomonas in light (phototaxis and stop responses) is controlled by a visual system with a rhodopsin as the functional photoreceptor. Here, we present evidence that in Chlamydomonas wild-type cells all-trans retinal is the predominant isomer and that it is present in amounts similar to that of the rhodopsin itself.The ability of different retinal isomers and analog compounds to restore photosensitivity in blind Chlamydomonas cells (strain CC2359) was tested by means of flash-induced light scattering transients or by measuring phototaxis in a taxigraph. All-trans retinal reconstitutes behavioral light responses within one minute, whereas cis-isomers require at least 50 x longer incubation times, suggesting that the retinal binding site is specific for all-trans retinal. Experiments with 13-demethyl(dm)-retinal and short-chained analogs reveal that only chromophores with a beta-methyl group and at least three double bonds in conjugation with the aldehyde mediate function. Because neither 13-dm-retinal, nor 9,12-phenylretinal restores a functional rhodopsin, a trans/13-cis isomerisation seems to take place in the course of the activation mechanism. We conclude that with respect to its chromophore, Chlamydomonas rhodopsin bears a closer resemblence to bacterial rhodopsins than to visual rhodopsins of higher animals.