- PALLADIUM-CATALYZED SYNTHESIS OF α,β-UNSATURATED KETONES FROM KETONES VIA ALLYL ENOL CARBONATES
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Allyl enol carbonates, prepared by quenching ketone enolates with allyl chloroformate, are converted to α,β-unsaturated ketones with Pd(OAc)2-dppe catalyst in CH3CN.
- Shimizu, Isao,Minami, Ichiro,Tsuji, Jiro
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- Aqueous Microdroplets Capture Elusive Carbocations
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Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. This field sprung to life with the discovery by Olah that a superacidic solution allowed the successful capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption to the gas phase for mass spectrometric detection. This was accomplished by employing desorption electrospray ionization mass spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained from different reactions (e.g., elimination, substitution, and oxidation). Solvent-dependent studies revealed that aqueous microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival of the reactive carbocation in a positively charged aqueous microdroplet and its subsequent ejection to the gas phase for mass spectrometric analysis.
- Kumar, Anubhav,Mondal, Supratim,Banerjee, Shibdas
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- Oxidation of ketone by palladium(II), α-hydroxyketone synthesis catalyzed by a bimetallic palladium(II) complex
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A bimetallic palladium(II) complex containing a triketone ligand and a bridging dinitrogen ligand oxidizes ketones in aqueous THF to α-hydroxyketone by a direct air oxidation. While the normal synthesis of α-hydroxyketones involves a series of reactions, this synthesis performs the transformation in one step in a catalytic air oxidation. This synthesis does not involve an olefin and is almost unprecedented in transition metal catalysis. Its main virtue is its simplicity and actually it is an enolization reaction. Methanesulfonic acid is used to accelerate the enolization of ketones. The reaction is carried out in the presence of CuCl2 and/or dioxygen only. In particular, it is found that the hydroxyketone formation does not require the presence of CuCl2. Matrix assisted laser desorption ionization (MALDI) and time-of-flight mass spectrometry (TOFMS) are used to record the mass spectra of α-hydroxyketones products. α-Cyano-4-hydroxycinnamic acid (CHCA) matrix promoted the molecular ion detection when 180 pmol of α-hydroxyketones is introduced into the TOFMS.
- El-Qisairi, Arab K,Qaseer, Hanan A
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- ENONE FORMATION FROM ALLYL β-KETO ESTERS ALKENYL ELLYL CARBONATES, SILYL ENOL ETHERS, AND ENOL ACETATES BY THE PHOSPHINE-FREE PALLADIUM CATALYST
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The effect of phosphine ligands on the palladium catalyzed enone formation from allyl β-keto esters, alkenyl allyl carbonates, silyl enol ethers, and enol acetates has been reinvestigated, and clean enone formation was observed by a phosphine-free palladium catalyst.
- Tsuji, Jiro,Minami, Ichiro,Shimizu, Isao,Kataoka, Hideaki
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- A NOVEL PALLADIUM-CATALYZED PREPARATIVE METHOD OF α,β-UNSATURATED KETONES AND ALDEHYDES FROM SATURATED KETONES AND ALDEHYDES VIA THEIR SILYL ENOL ETHERS
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Silyl enol ethers prepared from saturated ketones and aldehydes can be converted to α,β-unsaturated ketones and aldehydes by the reaction of allyl carbonate in the presence of palladium-phosphine complexes as a catalyst.The selection of solvent is crucial and nitriles are most effective as the solvent.
- Tsuji, Jiro,Minami, Ichiro,Shimizu, Isao
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- ONE-STEP SYNTHESIS OF α,β-UNSATURATED KETONES BY THE REACTION OF ENOL ACETATES WITH ALLYL METHYL CARBONATE CATALYZED BY PALLADIUM AND TIN COMPOUNDS
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Enol acetates derived from saturated ketones are converted to α,β-unsaturated ketones by heating with allyl methyl carbonate in MeCN by bimetallic catalysis of palladiumphosphine complex and tin methoxide.
- Tsuji, Jiro,Minami, Ichiro,Shimizu, Isao
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- Syntesis of 2-Cycloalken-1-ones
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The bromination of 2-alkyl- and 2-phenyl-1-cycloalkanones with N-bromosuccinimide and subsequent dehydrobromination with aniline gave the corresponding 2-cycloalken-1-ones.
- Shimazaki, Makoto,Huang, Zhi-Hui,Goto, Mikiko,Suzuki, Noriko,Ohta, Akihiro
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- Improved robustness of heterogeneous Fe-non-heme oxidation catalysts: A catalytic and EPR study
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There is currently a rarity in production and in-depth catalytic study of heterogeneous non-heme Fe catalysts. Herein, two heterogeneous catalysts have been synthesized by covalent grafting of non-heme Fe-complexes, DPEIFe IIICl and HFEIFeIIICl, on SiO2. The catalytic performance of the obtained DPEIFeIII@SiO2 and HFEIFe III@SiO2 materials has been systematically studied for catalytic oxidation of cyclohexene. The catalytic data show that the present non-heme Fe catalysts are functional and can achieve higher activity compared to other non-heme Fe reported so far in the literature. Importantly, the heterogeneneous catalysts show a remarkable robustness and improved oxidative stability vs. the homogeneous ones. Studies by UV-vis and EPR reveal a common mechanistic pattern: CH3CN interacts with the Fe-atom promoting the formation of a Low-Spin (S = 1/2) intermediate, in the presence of H 2O2, probably a FeIII-OOH hydroperoxide. The role of radical intermediates was investigated in detail by spin-trapping techniques. Finally, taking into account the nature of oxidation products, a consistent catalytic mechanism, valid for both homogeneous and heterogeneous catalysts, is discussed.
- Bilis,Stathi,Mavrogiorgou,Deligiannakis,Louloudi
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- Total Synthesis and Structure Revision of Halioxepine
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The first total synthesis of halioxepine is accomplished using a 1,4-addition for constructing the quaternary center at C10 and a halo etherification for the generation of the tertiary ether at C7. The correct structure of halioxepine was determined by assembling different enantiomeric building blocks and by changing the relative configuration between C10 and C15.
- Poock, Caroline,Kalesse, Markus
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p. 1615 - 1619
(2020/12/23)
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- CeO2-Supported Pd(II)-on-Au Nanoparticle Catalyst for Aerobic Selective α,β-Desaturation of Carbonyl Compounds Applicable to Cyclohexanones
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Direct selective desaturation of carbonyl compounds to synthesize α,β-unsaturated carbonyl compounds represents an environmentally benign alternative to classical stepwise procedures. In this study, we designed an ideal CeO2-supported Pd(II)-on-Au nanoparticle catalyst (Pd/Au/CeO2) and successfully achieved heterogeneously catalyzed selective desaturation of cyclohexanones to cyclohexenones using O2 in air as the oxidant. Besides cyclohexenones, various bioactive enones can also be synthesized from the corresponding saturated ketones under open air conditions in the presence of Pd/Au/CeO2. Preliminary mechanistic studies revealed that α-C-H bond cleavage in the substrates is the turnover-limiting step of this desaturation reaction.
- Jin, Xiongjie,Mizuno, Noritaka,Takei, Daisuke,Yabe, Tomohiro,Yamaguchi, Kazuya,Yatabe, Takafumi
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p. 5057 - 5063
(2020/05/27)
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- Combining Photo-Organo Redox- and Enzyme Catalysis Facilitates Asymmetric C-H Bond Functionalization
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In this study, we combined photo-organo redox catalysis and biocatalysis to achieve asymmetric C–H bond functionalization of simple alkane starting materials. The photo-organo catalyst anthraquinone sulfate (SAS) was employed to oxyfunctionalise alkanes to aldehydes and ketones. We coupled this light-driven reaction with asymmetric enzymatic functionalisations to yield chiral hydroxynitriles, amines, acyloins and α-chiral ketones with up to 99 % ee. In addition, we demonstrate functional group interconversion to alcohols, esters and carboxylic acids. The transformations can be performed as concurrent tandem reactions. We identified the degradation of substrates and inhibition of the biocatalysts as limiting factors affecting compatibility, due to reactive oxygen species generated in the photocatalytic step. These incompatibilities were addressed by reaction engineering, such as applying a two-phase system or temporal and spatial separation of the catalysts. Using a selection of eleven starting alkanes, one photo-organo catalyst and 8 diverse biocatalysts, we synthesized 26 products and report for the model compounds benzoin and mandelonitrile > 97 % ee at gram scale.
- Zhang, Wuyuan,Fueyo, Elena Fernandez,Hollmann, Frank,Martin, Laura Leemans,Pesic, Milja,Wardenga, Rainer,H?hne, Matthias,Schmidt, Sandy
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supporting information
p. 80 - 84
(2019/01/04)
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- Bridged bicyclic 2,3-dioxabicyclo[3.3.1]nonanes as antiplasmodial agents: Synthesis, structure-activity relationships and studies on their biomimetic reaction with Fe(II)
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Despite recent advancements in its control, malaria is still a deadly parasitic disease killing millions of people each year. Progresses in combating the infection have been made by using the so-called artemisinin combination therapies (ACTs). Natural and synthetic peroxides are an important class of antimalarials. Here we describe a new series of peroxides synthesized through a new elaboration of the scaffold of bicyclic-fused/bridged synthetic endoperoxides previously developed by us. These peroxides are produced by a straightforward synthetic protocol and are characterized by submicromolar potency when tested against both chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum strains. To investigate their mode of action, the biomimetic reaction of the representative compound 6w with Fe(II) was studied by EPR and the reaction products were characterized by NMR. Rationalization of the observed structure-activity relationship studies was performed by molecular docking. Taken together, our data robustly support the hypothesized mode of activation of peroxides 6a-cc and led to the definition of the key structural requirements responsible for the antiplasmodial potency. These data will pave the way in future to the rational design of novel optimized antimalarials suitable for in vivo investigation.
- D'Alessandro, Sarah,Alfano, Gloria,Di Cerbo, Luisa,Brogi, Simone,Chemi, Giulia,Relitti, Nicola,Brindisi, Margherita,Lamponi, Stefania,Novellino, Ettore,Campiani, Giuseppe,Gemma, Sandra,Basilico, Nicoletta,Taramelli, Donatella,Baratto, Maria Camilla,Pogni, Rebecca,Butini, Stefania
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- Cobalt-Catalyzed Regioselective Olefin Isomerization under Kinetic Control
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Olefin isomerization is a significant transformation in organic synthesis, which provides a convenient synthetic route for internal olefins and remote functionalization processes. The selectivity of an olefin isomerization process is often thermodynamically controlled. Thus, to achieve selectivity under kinetic control is very challenging. Herein, we report a novel cobalt-catalyzed regioselective olefin isomerization reaction. By taking the advantage of fine-tunable NNP-pincer ligand structures, this catalytic system features high kinetic control of regioselectivity. This mild catalytic system enables the isomerization of 1,1-disubstituted olefins bearing a wide range of functional groups in excellent yields and regioselectivity. The synthetic utility of this transformation was highlighted by the highly selective preparation of a key intermediate for the total synthesis of minfiensine. Moreover, a new strategy was developed to realize the selective monoisomerization of 1-alkenes to 2-alkenes dictated by installing substituents on the γ-position of the double bonds. Mechanistic studies supported that the in situ generated Co-H species underwent migratory insertion of double bond/β-H elimination sequence to afford the isomerization product. The less hindered olefin products were always preferred in this cobalt-catalyzed olefin isomerization due to an effective ligand control of the regioselectivity for the β-H elimination step.
- Liu, Xufang,Zhang, Wei,Wang, Yujie,Zhang, Ze-Xin,Jiao, Lei,Liu, Qiang
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p. 6873 - 6882
(2018/05/30)
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- Mild Chemoenzymatic Oxidation of Allylic sec-Alcohols. Application to Biocatalytic Stereoselective Redox Isomerizations
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The design of catalytic oxidative methodologies in aqueous medium under mild reaction conditions and using molecular oxygen as final electron acceptor represents a suitable alternative to the traditional oxidative transformations. These methods are especially relevant if other functionalities that can be oxidized are present within the same molecule, as in the case of allylic alcohols. Herein we apply a simple chemoenzymatic system composed of the laccase from Trametes versicolor and 2,2,6,6-tetramethylpiperidinyloxy radical (TEMPO) to oxidize a series of racemic allylic sec-alcohols into the corresponding α,β-unsaturated ketones. Afterward, these compounds react with different commercially available ene-reductases to afford the corresponding saturated ketones. Remarkably, in the case of trisubstituted alkenes, the bioreduction reaction occurred with high stereoselectivity. Overall, a bienzymatic one-pot two-step sequential strategy has been described with respect to the synthesis of saturated ketones starting from racemic allylic alcohols, thus resembling the metal-catalyzed redox isomerizations of these derivatives that have been previously reported in the literature.
- Martínez-Montero, Lía,Gotor, Vicente,Gotor-Fernández, Vicente,Lavandera, Iván
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p. 2413 - 2419
(2018/03/13)
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- Visible-light-driven photooxidation of alcohols using surface-doped graphitic carbon nitride
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Carbon-nanodot-doped g-C3N4 is used as a photocatalyst to promote the aerobic oxidation of alcohols and oxyfunctionalisation of activated hydrocarbons. A critical E-factor analysis of the current reaction system reveals its limitations en route to environmentally acceptable oxidation procedures.
- Zhang, Wuyuan,Bariotaki, Anna,Smonou, Ioulia,Hollmann, Frank
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supporting information
p. 2096 - 2100
(2017/07/24)
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- Selective Photooxidation Reactions using Water-Soluble Anthraquinone Photocatalysts
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The aerobic organocatalytic oxidation of alcohols was achieved by using water-soluble sodium anthraquinone sulfonate. Under visible-light activation, this catalyst mediated the aerobic oxidation of alcohols to aldehydes and ketones. The photo-oxyfunctionalization of alkanes was also possible under these conditions.
- Zhang, Wuyuan,Gacs, Jen?,Arends, Isabel W. C. E.,Hollmann, Frank
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p. 3821 - 3826
(2017/09/13)
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- Selective acceptorless dehydrogenation and hydrogenation by iridium catalysts enabling facile interconversion of glucocorticoids
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An iridium(III) pentamethylcyclopentadienyl catalyst supported by 6,6'-dihydroxy-2,2'-bipyridine displays exquisite selectivity in acceptorless alcohol dehydrogenation of cyclic α,β-unsaturated alcohols over benzylic and aliphatic alcohols under mild aqueous reaction conditions. Hydrogenation of aldehydes and ketones occurs indiscriminately using the same catalyst under hydrogen, although chemoselectivity could be achieved when other potentially reactive carbonyl groups present are sterically inaccessible. This chemistry was demonstrated in the reversible hydrogenation and dehydrogenation of the A ring of glucocorticoids, despite the presence of other alcohol/or carbonyl functionalities in rings C and D. NMR studies suggest that an iridium(III) hydride species is a key intermediate in both hydrogenation and dehydrogenation processes.
- Ngo, Anh H.,Adams, Michael J.,Do, Loi H.
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supporting information
p. 6742 - 6745
(2015/02/19)
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- Hydroxy chalcogenide-promoted Morita-Baylis-Hillman Alkylation reaction: Intermolecular applications with alkyl halides as electrophiles
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Hydroxysulfides acted as catalysts to promote the Morita-Baylis-Hillman alkylation reaction of cyclohexenones and dihydropyridinones. The procedure worked efficiently with a variety of halides as electrophiles. Side reactions were in competition with the MBH alkylation, but fine-tuning the reaction conditions minimized their occurence.
- Gradillas, Ana,Belmonte, Efres,Da Silva, Rondes Ferreira,Perez-Castells, Javier
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p. 1935 - 1941
(2014/04/03)
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- Hydroxy Chalcogenide-Promoted Morita-Baylis-Hillman Alkylation Reaction: Intermolecular Applications with Alkyl Halides as Electrophiles
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Hydroxysulfides acted as catalysts to promote the Morita-Baylis-Hillman alkylation reaction of cyclohexenones and dihydropyridinones. The procedure worked efficiently with a variety of halides as electrophiles. Side reactions were in competition with the
- Gradillas, Ana,Belmonte, Efres,Da Silva, Rondes Ferreira,Prez-Castells, Javier
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p. 1935 - 1941
(2015/10/05)
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- Multi-wall carbon nanotube-supported manganese(III) porphyrin: An efficient and reusable catalyst for the oxidation of alkenes with H2O 2 under ultrasonic irradiation
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A manganese complex of meso-tetrakis(p-hydroxyphenyl)porphyrin immobilized onto functionalized multi-wall carbon nanotubes has been synthesized and characterized. The catalytic activity of this heterogeneous catalyst was investigated in the oxidation of various olefins with hydrogen peroxide under ultrasonic irradiation. The role of the stoichiometric amounts of acetic anhydride/or acetic acid as an activator that introduces in situ peracetic acid is discussed. This heterogeneous catalyst was highly reusable in the oxidation reactions and reused several times without significant loss of its catalytic activity.
- Rayati, Saeed,Bohloulbandi, Elaheh
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- Intramolecular carbonickelation of alkenes
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The efficiency of the intramolecular carbonickelation of substituted allylic ethers and amines has been studied to evaluate the influence of the groups borne by the double bond on this cyclization. The results show that when this reaction takes place, it affords only the 5-exo-trig cyclization products, viz. dihydrobenzofurans or indoles. Depending on the tethered heteroatom (O or N), the outcome of the cyclization differs. While allylic ethers are relatively poor substrates that undergo a side elimination and need an intracyclic double bond to proceed, allylic amines react well and afford indoline and indole derivatives. Finally, the synthesis of the trinuclear ACE core of a morphine-like skeleton was achieved by using NiBr2bipy catalysis.
- Lhermet, Rudy,Durandetti, Muriel,Maddaluno, Jacques
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p. 710 - 716
(2013/06/05)
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- Hydrogenation of phenol using silica-supported Pd and PdAu catalysts in the presence of H2 and O2
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2-Cyclohexen-1-one can be synthesized from phenol using silica-supported Pd catalyst by hydrogenation under coexisting hydrogen and oxygen gases. The effects of hydrogen and oxygen ratio, solvent, and alloying Pd with Au were investigated. Similar transfo
- Okada, Shusuke,Fujiwara, Kensei,Kamegawa, Takashi,Mori, Kohsuke,Yamashita, Hiromi
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p. 1057 - 1059,3
(2020/08/24)
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- Old yellow enzyme-catalyzed dehydrogenation of saturated ketones
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Enzymes from extremophiles have always been of great interest for biotechnology because of their ruggedness against various stress factors. We have isolated, cloned, heterologously expressed and characterized a thermostable old yellow enzyme (OYE) from Geobacillus kaustophilus. In addition to the expected 'enone' reduction, GkOYE also catalyzes the reverse reaction, i.e., the desaturation of C-C bonds adjacent to a carbonyl to give the corresponding α,β-unsaturated ketone. The reaction proceeds at the expense of molecular oxygen without the need for a nicotinamide cofactor and represents an environmentally benign alternative to known chemical dehydrogenation methods.
- Schittmayer, Matthias,Glieder, Anton,Uhl, Michael K.,Winkler, Andreas,Zach, Simone,Schrittwieser, Joerg H.,Kroutil, Wolfgang,MacHeroux, Peter,Gruber, Karl,Kambourakis, Spiros,Rozzell, J. David,Winkler, Margit
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experimental part
p. 268 - 274
(2011/04/22)
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- Highly ordered mesoporous zirconia-polyoxometalate nanocomposite materials for catalytic oxidation of alkenes
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A series of well-ordered mesoporous ZrO2-based heteropoly acid nanocomposite frameworks has been prepared through a surfactant-assisted sol-gel copolymerization route. The pore walls of these materials consist of nanocrystalline tetragonal ZrO2 and Keggin-type 12-phosphomolybdic acid (PMA) components with different PMA loadings, i.e. 12, 22 and 37 wt%. Small angle X-ray scattering, high-resolution TEM and N2 physisorption measurements indicated mesoporous property in hexagonal p6mm symmetry with large internal BET surface areas and narrow-sized pores. The incorporated PMA clusters preserve intact their Keggin structure into the mesoporous frameworks according to EDX, FT-IR and diffuse-reflectance UV/vis/NIR spectroscopy. The obtained ZrO2-PMA nanocomposites demonstrated great application potential in oxidative catalysis, exhibiting exceptional stability and catalytic activity in oxidation of alkenes using hydrogen peroxide as oxidant. The Royal Society of Chemistry 2011.
- Armatas, Gerasimos S.,Bilis, Georgios,Louloudi, Maria
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experimental part
p. 2997 - 3005
(2011/10/05)
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- Synthesis and comparative antibacterial activity of verdamicin C2 and C2a. A new oxidation of primary allylic azides in dihydro[2H]pyrans
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(Chemical Equation Presented) A synthesis of verdamicin C2 and its congener C2a has been accomplished from sisomicin relying on a novel oxidative transformation of an allylic azide to the corresponding α,β- unsaturated aldehyde, and its stereocontrolled elaboration into the intended 5′ side chain of verdamicin C2 and C2a. In vitro antibacterial testing shows that both C6′ epimers in verdamicin C2 and C2a are equally active against a variety of bacterial strains. Oxidation of allylic primary azides, ethers, and esters of 2-substituted dihydro[2H]pyrans with SeO2 leads directly to the corresponding aldehydes.
- Hanessian, Stephen,Szychowski, Janek,Pablo Maianti
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supporting information; experimental part
p. 429 - 432
(2009/09/25)
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- From vinyl pyranoses to carbasugars by an iron-catalyzed reaction complementary to classical Ferrier carbocyclization
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Starting from vinyl pyranoses an iron-catalyzed tandem isomerization- intramolecular aldolization reaction was developed to prepare cyclohexenone derivatives bearing substituents on the double bond, and it has been applied in a short synthesis of 4-epi-ga
- Mac, Dinh Hung,Samineni, Ramesh,Petrignet, Julien,Srihari, Pabbaraja,Chandrasekhar, Srivari,Yadav, Jhillu Singh,Gree, Rene
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supporting information; experimental part
p. 4717 - 4719
(2010/01/16)
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- Facile synthesis of c/s-2-alkyl-3-trialkylsilyloxycycloalkanones via the non-aldol aldol rearrangement of 2,3-epoxycycloalkanols
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Silyl triflate-promoted rearrangement of c/s-2,3-epoxycycloalkanols A, prepared by epoxidation of the cyclic allylic alcohol and then sllylatlon, afforded good yields (~70-75%) of the c/s-2-alkyl-3-silyloxycycloalkanones B, presumably via the intermediates C and D, even with quite large α-substituents, e.g., terf-butyl. Finally, it has been shown that the stereochemistry of the epoxy alcohol is crucial as one would expect from the mechanism.
- Jung, Michael E.,Allen, Damian A.
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supporting information; experimental part
p. 2039 - 2041
(2009/04/18)
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- Cobalt-Catalyzed Oxidations in Volumetrically Expanded Liquids by Compressed Gases
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Oxidations of hydrocarbons, cycloalkanes and alkenes, arylalkanes, and a variety of other organic substrates are accomplished by cobalt-N-hydroxysuccinimide co-catalyzed reactions with dioxygen under unusually mild, near ambient conditions of temperature and pressure. The improved safety of the oxidation method and the high yields of product obtained make use of a unique combination of cobalt (II) complexes with N-hydroxysuccinimide. These autoxidation reactions do not have prolonged initiation times. Many of these reactions can be safely performed under normal chemical laboratory conditions and do not require specialized equipment or reagents.
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Page/Page column 8
(2008/12/06)
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- Enantioselective microbial oxidation of allyl alcohols
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A new route to the optically active allyl alcohols by microbial oxidation is disclosed. Yamadazyma farinosa IFO 10896, a yeast, efficiently catalyzes the enantioselective oxidation of allyl alcohols to afford the corresponding optically active alcohols as the remaining substrates. This reaction is applicable to both cyclic and acyclic compounds. Copyright
- Matsumoto, Kazutsugu,Kawabata, Yoichi,Okada, Satoshi,Takahashi, Jun,Hashimoto, Key,Nagai, Yuto,Tatsuta, Junichi,Hatanaka, Minoru
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p. 1428 - 1429
(2008/03/18)
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- Efficient palladium-catalyzed nucleophilic addition of triorganoindium reagents to carbocyclic derivatives
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Palladium (0)-catalyzed allylic substitution reactions employing triorganoindium reagents have been investigated. In situ generated vinyl- and arylindiums react with substituted and unsubstituted cyclohex-2-enyl esters in the presence of 1-3 mol % Pd2(dba)3 to produce vinyl- or arylcyclohexenes in moderate to excellent yields. The stereoselectivity of this process was also examined, and evidence is presented that the reaction proceeds with inversion of stereochemical configuration.
- Baker, Lucas,Minehan, Thomas
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p. 3957 - 3960
(2007/10/03)
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- Oxidation of silyl enol ethers by using IBX and IBX·N-oxide complexes: A mild and selective reaction for the synthesis of enones
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α,β-Unsaturated carbonyl compounds can be prepared by the oxidation of trimethylsilyl enol ethers with IBX (1) or IBX·MPO (2). A diverse set of carbonyl compounds can be dehydrogenated with ease by using this method. Trimethylsilyl enol ethers such as 4, which are formed in situ by the addition of an organometallic species to an enone, can be dehydrogenated with 1 or 2 to give a functionalized enone (e. g. 3 → 5). IBX = iodoxybenzoic acid; MPO = 4-methoxypyridine-N-oxide.
- Nicolaou,Gray, David L. F.,Montagnon, Tamsyn,Harrison, Scott T.
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p. 996 - 1000
(2007/10/03)
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- (2-hydroxy)ethyl-thioureas useful as modulators of alpha2B adrenergic receptors
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Compounds of formula (i) and of formula (ii) wherein the symbols have the meaning disclosed in the specification, specifically or selectively modulate α2B and/or α2C adrenergic receptors in preference over α2A adrenergic receptors, and as such are useful for alleviating chronic pain and allodynia and have no or only minimal cardivascular and/or sedatory activity.
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- Effect of cyclohexenonic long chain fatty alcohols on neurite outgrowth. Study on structure-activity relationship
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Four series of long chain fatty alcohols bearing a cyclohexenone moiety in addition to a ω-alkanol side chain were synthesized using 'Umpolung' reactivity strategy. Their effect on neurite outgrowth was evaluated by means of fetal rat neurons in culture. The length of the ω-hydroxy side chain is a crucial factor for biological activity.
- Girlanda-Junges, Celine,Keyling-Bilger, Florence,Schmitt, Gaby,Luu, Bang
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p. 7735 - 7748
(2007/10/03)
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- Highly stereo and chemoselective iron-catalyzed alkenylation of organomagnesium compounds
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In the presence of Fe(acac)3, Grignard reagents react readily with alkenyl halides (X = I, Br or Cl) in a THF/NMP mixture to give the cross-coupling products in high yields with an excellent stereoselectivity (≤99.5%). The scope of the reaction is very broad since a vast array of functional groups are tolerated (esters, nitriles, aromatic or aliphatic halides and even ketones). The procedure reported herein is an interesting alternative to the classical Pd- or Ni-catalyzed reactions, especially for preparative organic chemistry.
- Cahiez, Gerard,Avedissian, Hovsep
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p. 1199 - 1205
(2007/10/03)
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- A One-Pot Condensation of Pyrones and Enals. Synthesis of 1H,7H-5a,6,8,9-Tetrahydro-1-oxopyrano[4,3-6][1]benzopyrans
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Condensation of various 6-substituted 4-hydroxypyrones 1 with 1-cyclohexenecarboxaldehydes in the presence of L-proline in ethyl acetate gave high yields of substituted 1H,7H-5a,6,8,9-tetrahydro-1-oxopyrano[4,3-6][1]benzopyrans. The reaction presumably oc
- Hua, Duy H.,Chen, Yi,Sin, Hong-Sig,Maroto, Maria J.,Robinson, Paul D.,Newell, Steven W.,Perchellet, Elisabeth M.,Ladesich, James B.,Freeman, Jonathan A.,Perchellet, Jean-Pierre,Chiang, Peter K.
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p. 6888 - 6896
(2007/10/03)
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- Photoinduced electron transfer from enol silyl ethers to quinone. Part 1. Pronounced effects of solvent polarity and added salt on the formation of α-enones
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The enol silyl ethers (ESE) of various ketones are efficiently oxidized to the corresponding α, β-unsaturated enones (E) when a dichloromethane solution containing equimolar amounts of chloranil is irradiated with filtered light (λexc > 380 nm). The 1:1 adduct (A) of enol silyl ether and quinone is a byproduct, the structure of which is established by X-ray crystallography. Solvent polarity and added salts play a major role in establishing the product distribution between E and A. Such a medium effect, coupled with the ready isomerization of the kinetic-thermodynamic isomers derived from the silylation of 2-methylcyclohexanone, points to the cation radical of the enol silyl ether (ESE.+) as the reactive intermediate. A radical-ion pair mechanism involving the rapid one-electron oxidation of enol silyl ethers by photoactivated chloranil is discussed.
- Bockman, T. Michael,Shukla,Kochi, Jay K.
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p. 1623 - 1632
(2007/10/03)
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- Photoinduced electron transfer from enol silyl ethers to quinone. Part 2. Direct observation of ion-pair dynamics by time-resolved spectroscopy
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Time-resolved spectroscopy in two time domains (encompassing picoseconds and nanoseconds/microseconds) allows all the reactive intermediates involved in the photooxidation of enol silyl ethers (ESE) by chloranil (CA) to be identified, and each step in their temporal evolution to α-enone (E) and adduct (A) to be delineated.Thus, the radical-ion pair is the common intermediate formed in unit quantum yield via the highly efficient quenching of triplet chloranil by enol silyl ethers in both dichloromethane and acetonitrile.In the context of the Fuoss-Winstein formulation, the first-formed is a contact ion-pair, which in a non-polar solvent, such as dichloro-methane, predominantly suffers an initial ion-pair collapse (internal return) by β-proton transfer, and the resultant radical pair ultimately leads to α-enone (E).The contact ion-pair formed in the polar solvent undergoes diffusive separation, and the free ion ESE cation radical suffers desilylation by acetonitrile and ultimately leads to adduct (A).Added electrolyte to dichloromethane solutions modulates the ion-pair behaviour via the 'special salt effect' to divert the enone pathway to adduct formation.
- Bockman, T. Michael,Kochi, Jay K.
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p. 1633 - 1644
(2007/10/03)
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- Highly Regio- and Diastereoselective One-Pot Synthesis of Silyl Epoxy Alcohols and Vinylsilanes by Direct Hydroxy-Epoxidation
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A direct synthesis of silyl epoxy alcohols from vinylsilanes is described.It consists of the regioselective ene reaction of the vinylsilanes with singlet oxygen, which proceeds with predominant hydrogen abstraction at the position geminal to the silyl group.The resulting silyl allylic hydroperoxides were treated, without isolation, subsequently with Ti(O-i-Pr)4 to afford the silyl epoxy alcohols in good yields and very high diastereomeric ratios, which ranged from 93:7 to greater than 97:3.Alternatively, the vinylsilanes were photooxygenated directly in the presence of the titanium catalyst and the silyl epoxy alcohols obtained in good yields.The method was applied to di- and trisubstituted acyclic vinylsilanes with a methyl group geminal to silicon and cyclic derivatives all give consistently good results.In this novel hydroxy-epoxidation, the regioselectivity of the singlet oxygen ene reaction as well as the diastereoselectivity of the oxygen transfer can be controlled by the steering effects of the silyl group.
- Adam, Waldemar,Richter, Markus J.
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p. 3341 - 3346
(2007/10/02)
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- New synthetic applications of organotin compounds: Synthesis of stereodefined 2-iodo-2-alkenones, 2-substituted (E)-2-alkenones and 2-methyl-2-cycloalkenones
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Stereoisomeric mixtures of 3-iodo-3-nonen-2-one, 8a, 2-iodo-1-phenyl-2-octen-1-one, 8b, 2-iodo-1,3-diphenyl-2-propen-1-one, 8c, as well as (Z)-3-iodo-4-phenyl-3-buten-2-one, 8d, have been efficiently synthesized by a reaction sequence involving a Pd-catalyzed reaction between the corresponding 1-alkynyl ketones, 10, and Bu3SnH followed by iododestannylation. Stereomutation experiments carried out in the presence of daylight and using catalytic amounts of I2 showed that the Z stereoisomers of 8a, 8b and 8c, which could be separated by MPLC on silica gel from the corresponding E stereoisomers, as well as compound (Z)-8d were more stable than their E stereoisomers. Compounds 8a-d underwent Pd-catalyzed cross-coupling reactions with C6H5SnMe3, CH2=CH-SnBu3 and SnMe4 providing an efficient route to the corresponding 2-substituted 2-alkenones, 13. However, the Pd-catalyzed reaction between (Z)-8c and PhSnMe3 afforded a mixture of the expected cross-coupled product, (E)-13f with the compound derived from methyl transfer, (E)-13e. The couplings involving (Z)-8a, (Z)-8b, (Z)-8c and (Z)-8d proceeded with clean retention of stereochemistry, but the Pd-catalyzed reaction between (E)-8c and SnMe4 afforded a stereoisomeric mixture of 13e. On the contrary, the coupling between (E)/(Z)-8b and SnMe4 produced stereoisomerically pure (E)-13c. Two 2-iodo-2-cycloalkenones, i.e. compounds 18a and 18b, also reacted with SnMe4, in the presence of a Pd catalyst, to give the corresponding 2-methyl-2-cycloalkenones, 19a and 19b, respectively, in satisfactory yields. Compound 19b represents a very useful precursor to methylenomycin B, 9.
- Bellina, Fabio,Carpita, Adriano,Ciucci, Donatella,De Santis, Massimo,Rossi, Renzo
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p. 4677 - 4698
(2007/10/02)
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- SYNTHESES DE CYCLOHEXENONES α-SUBSTITUEES VIA LA THERMOLYSE DE CETOSULFOXYDES TERTIAIRES
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The sulfenylation-dehydrosulfenylation method, combined with carbon-carbon bond forming reactions, has been applied to the synthesis of some α-functionalized cyclohexenones 3.Hence, the sodium anion of the 2-methylthiocyclohexanone in THF reacts with primary, allyl and benzyl halides as well as with Michael acceptors to lead to the tertiary ketosulfides 1a-j.Further oxidation by NaIO4 and thermolysis in boiling toluene of the resulting sulfoxides 2 have been performed.The scope and limitations of this strategy are also discussed. Key Words: α-functionalized cyclohexenones; tertiary ketosulfides and ketosulfoxides; sulfenylation and deshydrosulfenylation; thermolysis.
- Barillier, Daniel,Benhida, Rachid,Vazeux, Michel
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- Direct α-hydroxylation of ketones under acidic conditions using [bis(trifluoroacetoxy)]iodobenzene
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[Bis(trifluoroacetoxy)] iodobenzene and trifluoroacetic acid in CH3CN/H2O reacts with aromatic, heteroaromatic, and aliphatic ketones to afford α-hydroxyketones in moderate to good yields.
- Moriarty,Berglund,Penmasta
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p. 6065 - 6068
(2007/10/02)
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- PHOTOCLEAVAGE OF CARBON-TIN BOND ACTIVATED BY NEIGHBORING
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β-Stannyl ketones underwent various types of reaction upon UV-irradiation, depending upon the substitution pattern of the substrate, and upon the solvent used.
- Sato, Tadashi,Takezoe, Kohji
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p. 4003 - 4006
(2007/10/02)
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- Selective Dimerization by Paired Electrolysis of Enol Acetate
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Electrolysis of enol esters of cyclic ketones possessing an alkyl group at the α-position using graphite carbon electrodes (EGM62 or EG10 : Nippon Carbon Co.Ltd.) brought about selective dimerization at the β-position of the ketones to give the corresponding 1,6-diketones in good to moderate yields.It was found that initial anodic formation of α,β-unsaturated ketones was successively followed by cathodic hydrodimerization (paired electrolysis) in an undivided cell.
- Maekawa, Hirofumi,Nakano, Kazuharu,Hirashima, Tsuneaki,Nishiguchi, Ikuzo
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p. 1661 - 1664
(2007/10/02)
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- Ultrasound-Promoted Cycloadditions in the Synthesis of Salvia miltiorrhiza Abietanoid o-Quinones
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The ultrasound-promoted Diels-Alder reaction of 3-methyl-4,5-benzofurandione with appropriately substituted vinylcyclohexenes has led to the synthesis of tanshinone IIA, nortanshinone, tanshindiol B, methyl tanshinonate, and tanshinone IIB, biologically active metabolites of the Chinese traditional medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge.Methyltanshinquinone, the dihydro derivative of the natural product, methylenetanshinquinone, was similarly prepared.The effect of ultrasound in promoting the cycloadditions parallels that of high pressure and improved the regioselectivity in favour of the natural isomers.
- Lee, Junning,Snyder, John K.
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p. 4995 - 5008
(2007/10/02)
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- t-BUTYLDIPHENYLSILYL-LITHIUM AND LITHIUM BIS(t-BUTYLDIPHENYLSILYL)CUPRATE. NEW SILYLATING REAGENTS.
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t-Butyldiphenylsilyl-lithium reacts with carbonyl derivatives to give α-hydroxysilanes in high yields.Lithium bis(t-butyldiphenylsilyl)cuprate reacts with α,β-unsaturated ketones and esters and with acyl chlorides to give β-silylcarbonyl compounds and acy
- Cuadrado, P.,Gonzalez, A.M.,Gonzalez, B.,Pulido, F.J.
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p. 275 - 284
(2007/10/02)
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- A Three-Step Pyridoannelation of Carbonyl Compounds
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The elaboration of a pyridine nucleus onto an α-methylene carbonyl compound can be accomplished through a three step reaction sequence based on the regiospecific alkylation of N,N-dimethylhydrazones with bromoethyl-1,3-dioxolane.Scope and limitations of the new method are considered.
- Marchetti, Mauro
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p. 1761 - 1765
(2007/10/02)
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- Process for preparing 4,4A,5,6-tetrahydro-7-methyl-2-(3H)-naphthalenone, intermediates used in said process and novel crystalline form of same
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Described is a process for preparing 4,4A,5,6-tetrahydro-7-methyl-2-(3H)-naphthalenone having the structure: STR1 and intermediates useful in such process defined according to the structure: STR2 wherein one of R3 or R4 is hydrogen a
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- Preparation of chiral allylic alcohols using Rhizopus nigricans. Use of the Harada-Nakanishi exciton chirality method for verifying configurational assignments of allylic alcohols
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A series of (R) acyclic and cyclic allylic alcohols was prepared by enantioselective hydrolysis of acetates using Rhizopus nigricans.The configurations of the alcohols formed were established by chemical methods and, in the case of 1,2-benzocyclohepta-1,3
- Ito, Satoru,Kasai, Masaji,Ziffer, Herman,Silverton, J.V.
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p. 574 - 582
(2007/10/02)
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- New Methods for the Syntheses of α,β-Unsaturated Ketones, Aldehydes, and Nitriles by the Palladium-Catalyzed Reactions of Allyl β-Oxo Esters, Allyl 1-Alkenyl Carbonates, and Allyl α-Cyano Esters
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Allyl β-oxo esters, allyl 1-alkenyl carbonates, and allyl α-cyano esters are converted into α,β-unsaturated ketones, aldehydes, and nitriles by palladium-catalyzed intramolecular decarboxylation-dehydrogenation.Palladium-phosphine complexes such as Pd(OAc)2-PPh3, Pd(OAc)2-dppe, or Pd2(dba)3*CHCl3-PPh3, are effective catalysts.Yields depend on solvents and on the mole ratio of palladium to phosphine.The optimum Pd/P ratio for each substrate was determined.Use of nitriles as solvents is essential for the dehydrogenation.
- Minami, Ichiro,Nisar, Mohammad,Yuhara, Masami,Shimizu, Isao,Tsuji, Jiro
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p. 992 - 998
(2007/10/02)
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- CLEAVAGE OF THE CARBON-OXYGEN BOND IN ACETALS WITH CHLOROMETHYL BUTYL ETHER
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In the reactions of cyclic acetals with chloromethyl butyl ether the carbon-oxygen bond of the acetals can be cleaved by the action of the α-halogeno ether.
- Musavirov, R. S.,Mullakhmetova, Z. F.,Nedogrei, E. P.,Gabdullina, L. L.,Kantor, E. A.,Rakhmankulov, D. L.
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