- Ruthenium containing hydrotalcite as a solid base catalyst for >C{double bond, long}C< double bond isomerization in perfumery chemicals
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Ruthenium containing hydrotalcite (Ru-Mg-Al) is used as a solid base catalyst for >C{double bond, long}C2 and Ru-alumina for isomerization of methyl chavicol to trans-anethole. Ru-Mg-Al catalyst was reused four times without loss in its activity, however, significant loss in the conversion of methyl chavicol and selectivity of trans-anethole was observed on reusability of other ruthenium impregnated catalysts. The conversion of methyl chavicol and selectivity of trans-anethole was found to increase on increasing the reaction temperature as well as amount of catalyst. At 0.005 g catalyst amount, 55% conversion of methyl chavicol with 68% selectivity of trans-anethole was observed that increased to 93% with 82% selectivity of trans-anethole at 0.05 g catalyst amount. On further increase in the amount of catalyst to 1 g, conversion increased to 98% with 88% selectivity of trans-anethole.
- Sharma, Sumeet K.,Parikh, Parimal A.,Jasra, Raksh V.
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Read Online
- Selectivity in the anodic oxidation of cis- and trans-methoxylated propenylbenzenes. A useful expedient for the preparation of pure cis-propenylbenzene derivatives
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Anodic oxidation of cis/trans mixtures of 1,2-dimethoxy-4-propenylbenzene, 4-methoxy-propenylbenzene, and 1,2-methylenedioxy-4-propenylbenzene led to preferential reaction of the trans-isomer. This result was applied to a preparative method for obtaining the pure (>98%) cis-isomer.
- Gates, Bradley D.,Swenton, John S.
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Read Online
- Iron Catalyzed Double Bond Isomerization: Evidence for an FeI/FeIII Catalytic Cycle
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Iron-catalyzed isomerization of alkenes is reported using an iron(II) β-diketiminate pre-catalyst. The reaction proceeds with a catalytic amount of a hydride source, such as pinacol borane (HBpin) or ammonia borane (H3N?BH3). Reactivity with both allyl arenes and aliphatic alkenes has been studied. The catalytic mechanism was investigated by a variety of means, including deuteration studies, Density Functional Theory (DFT) and Electron Paramagnetic Resonance (EPR) spectroscopy. The data obtained support a pre-catalyst activation step that gives access to an η2-coordinated alkene FeI complex, followed by oxidative addition of the alkene to give an FeIII intermediate, which then undergoes reductive elimination to allow release of the isomerization product.
- Woof, Callum R.,Durand, Derek J.,Fey, Natalie,Richards, Emma,Webster, Ruth L.
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supporting information
p. 5972 - 5977
(2021/03/17)
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- Highly Z-Selective Double Bond Transposition in Simple Alkenes and Allylarenes through a Spin-Accelerated Allyl Mechanism
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Double-bond transposition in alkenes (isomerization) offers opportunities for the synthesis of bioactive molecules, but requires high selectivity to avoid mixtures of products. Generation of Z-alkenes, which are present in many natural products and pharmaceuticals, is particularly challenging because it is usually less thermodynamically favorable than generation of the E isomers. We report a β-dialdiminate-supported, high-spin cobalt(I) complex that can convert terminal alkenes, including previously recalcitrant allylbenzenes, to Z-2-alkenes with unprecedentedly high regioselectivity and stereoselectivity. Deuterium labeling studies indicate that the catalyst operates through a π-allyl mechanism, which is different from the alkyl mechanism that is followed by other Z-selective catalysts. Computations indicate that the triplet cobalt(I) alkene complex undergoes a spin state change from the resting-state triplet to a singlet in the lowest-energy C-H activation transition state, which leads to the Z product. This suggests that this change in spin state enables the catalyst to differentiate the stereodefining barriers in this system, and more generally that spin-state changes may offer a route toward novel stereocontrol methods for first-row transition metals.
- Kim, Daniel,Pillon, Guy,Diprimio, Daniel J.,Holland, Patrick L.
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supporting information
p. 3070 - 3074
(2021/03/08)
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- An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne cis-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
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The selective synthesis of Z-alkenes in alkyne semihydrogenation relies on the reactivity difference of the catalysts toward the starting materials and the products. Here we report Z-selective semihydrogenation of alkynes with ethanol via a coordination-induced ionic monohydride mechanism. The EtOH-coordination-driven Cl- dissociation in a pincer Ir(III) hydridochloride complex (NCP)IrHCl (1) forms a cationic monohydride, [(NCP)IrH(EtOH)]+Cl-, that reacts selectively with alkynes over the corresponding Z-alkenes, thereby overcoming competing thermodynamically dominant alkene Z-E isomerization and overreduction. The challenge for establishing a catalytic cycle, however, lies in the alcoholysis step; the reaction of the alkyne insertion product (NCP)IrCl(vinyl) with EtOH does occur, but very slowly. Surprisingly, the alcoholysis does not proceed via direct protonolysis of the Ir-C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl- ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)-H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting the alcoholysis. The 1-amine-EtOH catalytic system exhibits an unprecedented level of substrate scope, generality, and compatibility, as demonstrated by Z-selective reduction of all alkyne classes, including challenging enynes and complex polyfunctionalized molecules. Comparison with a cationic monohydride complex bearing a noncoordinating BArF- ion elucidates the beneficial role of the Cl- ion in controlling the stereoselectivity, and comparison between 1-amine-EtOH and 1-NaOtBu-EtOH underscores the fact that this base variable, albeit in catalytic amounts, leads to different mechanisms and consequently different stereoselectivity.
- Huang, Zhidao,Wang, Yulei,Leng, Xuebing,Huang, Zheng
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supporting information
p. 4824 - 4836
(2021/04/07)
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- Nickel-Catalyzed Allylic C(sp2)–H Activation: Stereoselective Allyl Isomerization and Regiospecific Allyl Arylation of Allylarenes
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Stereoselective allyl isomerization and regiospecific allyl arylation reactions of allylarenes with a catalytic system comprising nickel(II) with an aryl Grignard reagent were studied. Both reactions are triggered by allylic internal C(sp2)–H activation by in-situ-formed Ni0, which is inserted into the C–H bond at the 2-position of the allyl moiety without a directing group. The isomerization of allylarene to 1-propenylarene favors the E isomer and proceeds with quantitative conversion. The arylation takes place through oxidative cross-coupling of allylarenes with excess Grignard reagent. It occurs regiospecifically at the position of C(sp2)–H activation and represents a new method for the synthesis of 1,1-disubstituted olefins. The results of deuterium labeling experiments reveal an alkenyl/alkyl mechanism involving allylic internal C(sp2)–H activation and multiple intermolecular 1,2-, 1,3-, and 2,3-hydride shifts. These methods represent new approaches to the functionalization of olefins, and the mechanistic investigations could be helpful for the discovery and design of new strategies for olefin functionalization.
- Wu, Qiang,Wang, Lanlan,Jin, Rizhe,Kang, Chuanqing,Bian, Zheng,Du, Zhijun,Ma, Xiaoye,Guo, Haiquan,Gao, Lianxun
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p. 5415 - 5422
(2016/11/22)
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- Rhodium catalyzed aqueous biphasic hydroformylation of naturally occurring allylbenzenes in the presence of water-soluble phosphorus ligands
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The rhodium-catalyzed hydroformylation of eugenol was performed in aqueous biphasic systems using various water soluble phosphines: TPPTS (triphenylphosphinetrisulphonated); BDPPETS (bisdiphenylphosphinoethanetetrasulphonated), BDPPPTS (bisdiphenylphosphi
- Baricelli, Pablo J.,Rodriguez, Mariandry,Melean, Luis G.,Alonso, Maria Modro?o,Borusiak, Margarita,Rosales, Merlin,Gonzalez, Beatriz,De Oliveira, Kelley C. B.,Gusevskaya, Elena V.,Dos Santos, Eduardo N.
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p. 163 - 169
(2015/05/05)
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- Photocatalytic synthesis of dihydrobenzofurans by oxidative [3+2] cycloaddition of phenols
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We report a protocol for oxidative [3+2] cycloadditions of phenols and alkenes applicable to the modular synthesis of a large family of dihydrobenzofuran natural products. Visible-light-activated transition metal photocatalysis enables the use of ammonium persulfate as an easily handled benign terminal oxidant. The broad range of organic substrates that are readily oxidized by photoredox catalysis suggests that this strategy may be applicable to a variety of useful oxidative transformations.
- Blum, Travis R.,Zhu, Ye,Nordeen, Sarah A.,Yoon, Tehshik P.
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supporting information
p. 11056 - 11059
(2015/03/30)
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- Catalytic wittig reactions of semi- and nonstabilized ylides enabled by ylide tuning
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The first examples of catalytic Wittig reactions with semistabilized and nonstabilized ylides are reported. These reactions were enabled by utilization of a masked base, sodium tert-butyl carbonate, and/or ylide tuning. The acidity of the ylide-forming proton was tuned by varying the electron density at the phosphorus center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity up to >95:5, E/Z. Time for a tune up: Catalytic Wittig reactions with semi- and nonstabilized ylides were enabled by use of a masked base (NaOCO2tBu) and/or ylide tuning. The acidity of the ylide-forming proton was tuned by varying the electron density at the P center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity.
- Coyle, Emma E.,Doonan, Bryan J.,Holohan, Andrew J.,Walsh, Killian A.,Lavigne, Florie,Krenske, Elizabeth H.,O'Brien, Christopher J.
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supporting information
p. 12907 - 12911
(2016/02/18)
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- METHODS FOR PHOSPHINE OXIDE REDUCTION IN CATALYTIC WITTIG REACTIONS
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A method for increasing the rate of phosphine oxide reduction, preferably during a Wittig reaction comprising use of an acid additive is provided. A room temperature catalytic Wittig reaction (CWR) the rate of reduction of the phosphine oxide is increased due to the addition of the acid additive is described. Furthermore, the extension of the CWR to semi-stabilized and non-stabilized ylides has been accomplished by utilization of a masked base and/or ylide-tuning.
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Page/Page column 59; 68; 69
(2014/09/29)
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- Highly active and selective platinum(II)-catalyzed isomerization of allylbenzenes: Efficient access to (E)-anethole and other fragrances via unusual agostic intermediates
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Terminal alkene isomerization reactions can be efficiently catalyzed by PtII complexes bearing a chelating diphosphine and an alkyl or, better, aryl moiety under mild experimental conditions. In particular diphosphines, such as dppb, characterized by a large bite angle in conjunction with a pentafiuorophenyl residue coordinated to Pt enable quantitative conversion of the reagent into internal, alkenes within few hours at 50 °C in CHCl3 as solvent. E/Z selectivity can be as high as 98:2 for allylbenzene, and the catalytic system can be fruitfully applied to the preparation of E fragrances derived by isomerization of substituted, allylbenzene derivatives. The selectivity increases during the progress of the reaction because of a subsequent catalytic step where the Z alkene coordinates to the Pt and is converted into the E isomer. NMR investigation on the catalyst showed formation of agostic Pt...H intermediate species derived by insertion of the substrate into the Pt-aryl bond followed by β-hydride elimination. Formation of such agostic species is promoted by the steric hindrance imparted by the diphosphine characterized by a large bite angle. Kinetic studies and DFT calculations on the possible agostic intermediates shed light on their structure and enable the formulation of a possible catalytic mechanism.
- Scarso, Alessandro,Colladon, Marco,Sgarbossa, Paolo,Santo, Claudio,Michelin, Rino A.,Strukul, Giorgio
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experimental part
p. 1487 - 1497
(2010/05/15)
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- Fast and green microwave-Assisted conversion of essential oil allylbenzenes into the corresponding aldehydes via alkene isomerization and subsequent potassium permanganate promoted oxidative alkene group cleavage
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Essential oil allylbenzenes from have been converted quickly and efficiently into the corresponding benzaldehydes in good yields by a two-step "green" reaction pathway based on a solventless alkene group isomerization by KF/Al2O3 to form the corresponding l-arylpropene and a subsequent solventless oxidation of the latter to the corresponding benzaldehyde by KMnO4/CuSO4-5H2O. The assistance by microwave irradiation results in very short reaction times (2O3 under solvent-free conditions, respectively.
- Luu, Thi Xuan Thi,Lam, Trinh To,Le, Thach Ngoc,Duus, Fritz
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experimental part
p. 3411 - 3424
(2010/01/16)
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- Stereoselective Wittig olefination reactions employing a novel ortho-P-aryl alkoxide effect
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Non-stabilized ortho-P-alkoxy-substituted ylides react with aromatic and aliphatic aldehydes providing (E)-olefins with high stereocontrol, also allowing easy phosphine oxide removal in certain cases.
- McNulty, James,Keskar, Kunal
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experimental part
p. 7054 - 7057
(2009/04/07)
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- Proazaphosphatrane P(RNCH2CH2)3N (R = Me, i-Pr)-catalyzed isomerization of allylaromatics, allyl phenyl sulfide, allyl phenyl sulfone, and bis-allymethylene double bond-containing compounds
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Using a proazaphosphatrane catalyst, P(RNCH2CH2) 3N (R = Me, i-Pr), allylaromatics and allyl phenyl sulfide were selectively isomerized to the corresponding vinyl isomers in yields up to > 99% in CH3CN at 40°C. Efficient transformation of allyl phenyl sulfone at ambient temperature afforded an isomerization/dimerization product in >95% yield. Conjugation of bis-allylmethylene double bond-containing compounds gave the corresponding conjugated isomers for cis,cis-9,12- octadecadienol and its methyl ether in yields up to 97%, and desilylation/conjugation products were obtained from the catalytic reaction of the trimethylsilyl ether of cis,cis-9,12-octadecadienol. The reaction mechanism is discussed based upon the 1H and 31P NMR-monitored reactions in CD3CN or CH3CN under the reaction conditions.
- Yu, Zhengkun,Yan, Shenggang,Zhang, Guangtao,He, Wei,Wang, Liandi,Li, Yu,Zeng, Fanlong
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p. 111 - 117
(2007/10/03)
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- Three-component synthesis of (E)-α,β-unsaturated amides of the piperine family
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Selective formation of (E)-α,β-unsaturated amides by intermolecular three-component reaction between aldehydes, amines (1° or 2°) and ketenylidenetriphenylphosphorane (Ph3P=C=C=O) is described. Natural amides such as fagaramide and piperines could be prepared from immediately available educts. The method is shown to be extendable to the preparation of thioesters from thiols and aldehydes.
- Schobert,Siegfried,Gordon
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p. 2393 - 2397
(2007/10/03)
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- A novel thienylhydrazone, (2-thienylidene)3,4-methylenedioxybenzoylhydrazine, increases inotropism and decreases fatigue of skeletal muscle
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This study was designed to investigate the effects on single skeletal muscle fibers of a novel thienylhydrazone, referred to as LASSBio-294, which is a bioisoster of pyridazinone compounds that inhibit the cyclic AMP-specific phosphodiesterase (PDE) 4. Twitch and fatigue were analyzed in single skeletal muscle fibers isolated from either the semitendinous or the tibialis anterior muscles dissected from the frog Rana pipiens. LASSBio-294 (12.5-100 μM) increased twitch tension, accelerated the maximal rate of tension decay during relaxation, and had very little effect in the maximal rate of tension development of muscle fibers directly stimulated at ≤30 Hz. The positive inotropic effect of LASSBio-294 developed slowly, reaching its maximum at 40 min and was inversely proportional to the frequency of stimulation, becoming negligible at 60 and 90 Hz. The concentration-response relationship for LASSBio-294-induced potentiation of twitch tension was bell-shaped, with maximal effect occurring at 25 μM. In addition, LASSBio-294 reduced development of fatigue induced by tetanic stimulation of the muscle fibers and reduced the time needed for 80% prefatigue tension recovery after fatigue had developed to 50% of the maximal pretetanic force. These effects of LASSBio-294 can be fully explained by stimulation of the sarcoplasmic reticulum Ca2+ pump and could be ascribed to an increase in cellular levels of cyclic AMP due to PDE inhibition. The novel thienylhydrazone LASSBio-294 may be useful for treatment of patients suffering from conditions in which muscle fatigue is a debilitating symptom (e.g., chronic heart failure).
- Gonzalez-Serratos, Hugo,Chang, Ruzhang,Pereira, Edna F. R.,Castro, Newton G.,Aracava, Yasco,Melo, Paulo A.,Lima, Patricia C.,Fraga, Carlos A. M.,Barreiro, Eliezer J.,Albuquerque, Edson X.
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p. 558 - 566
(2007/10/03)
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- Further improvements in isomerization of olefins in solvent-free conditions
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Isomerization of safrole and ethyleugenol are performed quasi-quantitatively within 5 minutes at 80°C using KOH or KOtBu and catalytic amount of transfer agent in the absence of solvent. Transfer agent can be avoided in the case of KOtBu with eventually increase in reaction time. Isolated yields of 99% are obtained from 10 g of materials.
- Thach,Hanh,Hiep,Radhakrishna,Singh,Loupy
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p. 1379 - 1384
(2007/10/02)
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- The Stereocontrolled Horner-Wittig Reaction: Synthesis of Disubstituted Alkenes
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Addition of the lithium derivatives of phosphine oxides Ph2P(O)CH2R1 to aldehydes gives erythro adducts (11) with good stereoselectivity.Reduction of α-diphenylphosphinoyl ketones (12) gives threo adducts (11) with even better stereoselectivity.Purification by flash chromatography and/or crystallisation followed by elimination of Ph2PO2 gives pure Z- or E-alkenes with high material conversion.Explanations are offered for the stereoselectivities, conditions defined for full stereochemical control, and guidelines suggested for approaches to a given alkene.
- Buss, Antony D.,Warren, Stuart
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p. 2307 - 2326
(2007/10/02)
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- CIS-OLEFINS FROM THE HORNER-WITTIG REACTION; ORIGIN AND OPTIMISATION OF STEREOCHEMISTRY
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Conditions are described to produce high yields of erythro Horner-Wittig intermediates: stereospecific elimination gives cis-alkenes.
- Buss, Antony D.,Warren, Stuart
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p. 3931 - 3934
(2007/10/02)
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- Stereochemically Pure E- and Z-Alkenes by the Wittig-Horner Reaction
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Pure Z-alkenes are obtained stereospecifically from erythro-alcohols (3) formed on addition of Ph2PO-stabilised anions to aldehydes; acylation of the same anions, reduction of the α-Ph2P(O) ketones (5) to the threo-alcohol (6), and elimination gives pure E-alkenes.
- Buss, Antony D.,Warren, Stuart
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p. 100 - 101
(2007/10/02)
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