- Stereoselective Iridium-N,P-Catalyzed Double Hydrogenation of Conjugated Enones to Saturated Alcohols
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Asymmetric hydrogenation of prochiral substrates such as ketones and olefins constitutes an important instrument for the construction of stereogenic centers, and a multitude of catalytic systems have been developed for this purpose. However, due to the different nature of the π-system, the hydrogenation of olefins and ketones is normally catalyzed by different metal complexes. Herein, a study on the effect of additives on the Ir-N,P-catalyzed hydrogenation of enones is described. The combination of benzamide and the development of a reactive catalyst unlocked a novel reactivity mode of Crabtree-type complexes toward C=O bond hydrogenation. The role of benzamide is suggested to extend the lifetime of the dihydridic iridium intermediate, which is prone to undergo irreversible trimerization, deactivating the catalyst. This unique reactivity is then coupled with C=C bond hydrogenation for the facile installation of two contiguous stereogenic centers in high yield and stereoselectivity (up to 99% ee, 99/1 d.r.) resulting in a highly stereoselective reduction of enones.
- Andersson, Pher G.,Krajangsri, Suppachai,Peters, Bram B. C.,Zheng, Jia
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- Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones
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Enantiopure secondary alcohols are fundamental high-value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.
- Titze, Marvin,Heitk?mper, Juliane,Junge, Thorsten,K?stner, Johannes,Peters, René
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supporting information
p. 5544 - 5553
(2021/02/05)
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- Hydroperoxidations of Alkenes using Cobalt Picolinate Catalysts
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Hydroperoxides were synthesized in one step from various alkenes using Co(pic)2as the catalyst with molecular oxygen and tetramethyldisiloxane (TMDSO). The hydration product could be obtained using a modified catalyst, Co(3-mepic)2, with molecular oxygen and phenylsilane. Formation of hydroperoxides occurred through a rapid Co-O bond metathesis of a peroxycobalt compound with isopropanol.
- Peralta-Neel, Zulema,Woerpel
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supporting information
p. 5002 - 5006
(2021/06/30)
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- Method for hydrocarbylation synthesis of trisubstituted and tetrasubstituted olefins from non-terminal olefins
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The invention discloses a method for hydrocarbylation synthesis of trisubstituted and tetrasubstituted olefins from non-terminal olefins, wherein the method comprises the steps: carrying out hydrocarbylation reaction on the non-terminal olefins and sulfoxide in the presence of ferric salt and hydrogen peroxide, carrying out one-pot reaction on disubstituted non-terminal olefins to generate the trisubstituted olefins, and carrying out one-pot reaction on the trisubstituted non-terminal olefins to generate the tetrasubstituted olefins. In the method, sulfoxide is simultaneously used as a hydrocarbylation reagent and a solvent of olefins, and one more hydrocarbyl substituent is added to a reaction product compared with a double-bond carbon atom of a reactant, so that an olefin carbon chain isincreased; the reaction conditions are mild, the selectivity is good, the yield is high, and industrial production is facilitated.
- -
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Paragraph 0054-0058; 0067-0069
(2021/02/06)
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- Highly Enantioselective Iridium-Catalyzed Hydrogenation of Conjugated Trisubstituted Enones
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Asymmetric hydrogenation of conjugated enones is one of the most efficient and straightforward methods to prepare optically active ketones. In this study, chiral bidentate Ir-N,P complexes were utilized to access these scaffolds for ketones bearing the stereogenic center at both the α- and β-positions. Excellent enantiomeric excesses, of up to 99%, were obtained, accompanied with good to high isolated yields. Challenging dialkyl substituted substrates, which are difficult to hydrogenate with satisfactory chiral induction, were hydrogenated in a highly enantioselective fashion.
- Peters, Bram B. C.,Jongcharoenkamol, Jira,Krajangsri, Suppachai,Andersson, Pher G.
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p. 242 - 246
(2021/01/13)
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- Method for synthesizing alkyl olefin through coupling of double-bond carbon-hydrogen bond and saturated carbon-hydrogen bond
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The invention discloses a method for synthesizing alkyl olefin through coupling of a double-bond carbon-hydrogen bond and a saturated carbon-hydrogen bond. According to to the method, one-pot reactionis implemented on olefin and sulfoxide in the presence of ferric salt and hydrogen peroxide to generate alkyl olefin; in the method, sulfoxide is simultaneously used as a hydrocarbylation reagent anda solvent of olefin, and a reaction product is alkyl olefin from sulfoxide alkyl coupled with olefin carbon atoms, so that an olefin carbon chain is increased; the reaction conditions are mild, the selectivity is good, the yield is high, and industrial production is facilitated.
- -
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Paragraph 0060-0069; 0091
(2021/02/10)
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- Capturing the Monomeric (L)CuH in NHC-Capped Cyclodextrin: Cavity-Controlled Chemoselective Hydrosilylation of α,β-Unsaturated Ketones
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The encapsulation of copper inside a cyclodextrin capped with an N-heterocyclic carbene (ICyD) allowed both to catch the elusive monomeric (L)CuH and a cavity-controlled chemoselective copper-catalyzed hydrosilylation of α,β-unsaturated ketones. Remarkably, (α-ICyD)CuCl promoted the 1,2-addition exclusively, while (β-ICyD)CuCl produced the fully reduced product. The chemoselectivity is controlled by the size of the cavity and weak interactions between the substrate and internal C?H bonds of the cyclodextrin.
- Bistri-Aslanoff, Olivia,Derat, Etienne,Leloux, Sébastien,Leyssens, Tom,Ménand, Micka?l,Meijide Suárez, Jorge,Riant, Olivier,Roland, Sylvain,Sollogoub, Matthieu,Xu, Guangcan,Zhang, Pinglu,Zhang, Yongmin
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supporting information
p. 7591 - 7597
(2020/03/23)
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- Thermal decarboxylative Nazarov cyclization of cyclic enol carbonates involving chirality transfer
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Decarboxylative Nazarov cyclization of chiral cyclic enol carbonates proceeded to afford chiral 2-cyclopentenones with excellent chirality transfer under thermal conditions without any catalyst. Interestingly, the thermal decarboxylative Nazarov cyclization furnished the desired product with better chirality transfer than the Lewis acid-catalyzed reaction.
- Kozuma, Akane,Komatsuki, Keiichi,Saito, Kodai,Yamada, Tohru
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supporting information
p. 60 - 63
(2019/12/12)
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- Decarboxylative Nazarov Cyclization-Based Chirality Transfer for Asymmetric Synthesis of 2-Cyclopentenones
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Asymmetric synthesis of 2-cyclopentenones was achieved by chirality transfer based on Lewis acid catalyzed decarboxylative Nazarov cyclization of optically active cyclic enol carbonates, which are prepared by silver-catalyzed carbon dioxide incorporation into optically pure propargyl alcohols. The stereochemistry at the 4,5-positions of the 2-cyclopentenones was cleanly constructed by reflecting the stereochemistry of the starting materials. This method could be applied to various substrates to obtain the corresponding products in high yields with highly efficient chirality transfer.
- Komatsuki, Keiichi,Kozuma, Akane,Saito, Kodai,Yamada, Tohru
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supporting information
p. 6628 - 6632
(2019/09/03)
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- Nucleophilic Organic Base DABCO-Mediated Chemospecific Meinwald Rearrangement of Terminal Epoxides into Methyl Ketones
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Nucleophilic organic base DABCO (1,4-diazabicyclo[2.2.2]octane)-mediated Meinwald rearrangement of various epoxides was investigated. 2-Aryl-, alkenyl-, and alkynylepoxides generate the corresponding methyl ketones chemospecifically in good to excellent yields. The current DABCO-mediated Meinwald rearrangement of epoxides features readily accessible starting materials, a wide substrate scope, a transition-metal- and acid-free environment, and chemospecificity in the isomerization of epoxides.
- Li, Siqi,Shi, Yi,Li, Pingfan,Xu, Jiaxi
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p. 4443 - 4450
(2019/04/30)
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- Bovine serum albumin-catalysed cross aldol condensation: Influence of ketone structure
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Bovine serum albumin (BSA) catalyses the cross aldol condensation and proved to be catalytically active at mild temperature and in ethanol, a cheap and green solvent, contrasting with the strong or expensive reaction media usually employed for this reaction. We herein report the reaction of a set of ketones (butanone, 3-pentanone, cyclopentanone and cyclohexanone) with benzaldehyde and p-nitrobenzaldehyde which provided high conversions (77–95%) of the corresponding enones (isolated in a range of yields from 19% to 74%). Parameters assayed to achieve these conversion values were solvent, ketone/aldehyde molar ratio and temperature. In this procedure only cyclohexanone gave the bis-enone, by-product of the conventional aldol condensation, in low amount even at high benzaldehyde/cyclohexanone molar excess. Under the assayed conditions null or low ketol amounts were observed, except for the reaction of cyclopentanone and p-nitrobenzaldehyde. Moreover, kinetic data of BSA-catalysed aldol condensation of cyclohexanone and p-nitrobenzaldehyde suggest an ordered bi bi mechanism for enone formation; an enamine mechanism involving residues of the catalytic cavity exhibiting abnormal pKa values is also proposed.
- Ardanaz, Sebastián M.,Borucki, Estefanía L.,Velez Rueda, Ana J.,Parisi, Gustavo,Iribarren, Adolfo M.,Iglesias, Luis E.
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- Extractive biocatalysis in the asymmetric reduction of α-alkyl, β-aryl enones by Baker's yeast
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We prepared various chiral α-alkyl, β-aryl ketones with good to excellent enantiomeric excess through the Baker's yeast asymmetric double-bond reduction of the corresponding α,β-unsaturated substrates adsorbed onto the resin Amberlite XAD-7. This methodology was compatible with substrates bearing both electron-donating and withdrawing groups attached to the aromatic ring. Elongation of the α-alkyl substituent of the starting material strongly affected the reactivity and enantioselectivity of the reaction.
- Silva, Rafaela M.,Okano, Laura T.,Rodrigues, J. Augusto R.,Clososki, Giuliano C.
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p. 939 - 944
(2017/07/11)
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- Stereospecific Decarboxylative Nazarov Cyclization Mediated by Carbon Dioxide for the Preparation of Highly Substituted 2-Cyclopentenones
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Highly substituted 2-cyclopentenones were stereospecifically and regioselectively constructed with high catalytic efficiency through Lewis-acid catalyzed decarboxylative Nazarov cyclization of the cyclic carbonate derivative, which is prepared by reacting the propargyl alcohol with carbon dioxide in the presence of a silver catalyst. The stereochemistry of the 2-cyclopentenone is strictly controlled by the geometry of the alkene in the starting material. This method is applicable for various substrates.
- Komatsuki, Keiichi,Sadamitsu, Yuta,Sekine, Kohei,Saito, Kodai,Yamada, Tohru
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supporting information
p. 11594 - 11598
(2017/09/11)
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- Tuning the Reactivity of Functionalized Diallylic Alcohols: Br?nsted versus Lewis Acid Catalysis
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The chemodivergent reactivity of bifunctional, enol thioether-containing diallylic alcohols in acidic medium is disclosed, highlighting the difference between strong Lewis acid and mild Br?nsted acid catalysis. In the presence of bismuth(III) triflate, allylic alcohol activation affords diversely substituted cyclopentenones in a Nazarov-type electrocyclization, whereas activation of the thioenol ether by p-toluenesulfonic acid provides an entry to α-sulfenylated β,γ-unsaturated ketones. Both methods represent a facile access to the corresponding products under mild conditions, using inexpensive and non-toxic catalytic systems.
- Lempenauer, Luisa,Du?ach, Elisabet,Lemière, Gilles
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supporting information
p. 10285 - 10288
(2017/08/07)
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- Multi-enzyme cascade synthesis of the most odorous stereoisomers of the commercial odorant Muguesia
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The most odorous stereoisomers of the chiral commercial fragrance Muguesia are prepared by a very effective linear biocatalysed cascade reaction, in which a suitable unsaturated ketone is submitted to the sequential action of two enzymes, an ene-reductase and an alcohol dehydrogenase, which are added together to the same reaction vessel with the cofactor regeneration system. Two stereogenic centres in 1,2 relative position are thus created under high stereochemical control by a two-step one-pot enzymatic procedure.
- Brenna, Elisabetta,Crotti, Michele,Gatti, Francesco G.,Monti, Daniela,Parmeggiani, Fabio,Pugliese, Andrea,Santangelo, Sara
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- Unsymmetrical 1,5-diaryl-3-oxo-1,4-pentadienyls and their evaluation as antiparasitic agents
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In this work the synthesis and antiparasitical activity of new 1,5-diaryl-3-oxo-1,4-pentadienyl derivatives are described First, compounds 1a, 1b, 1c and 1d were prepared by acid-catalyzed aldol reaction between 2-butanone and benzaldehyde, anisaldehyde, p-N,N-dimethylaminobenzaldehyde and p-nitrobenzaldehyde Reacting each of the methyl ketones 1a, 1b, 1c and 1d with the p-substituted benzaldehydes under basic-catalyzed aldol reaction, we further prepared compounds 2a-2p All twenty compounds were evaluated for antiproliferative activity, particularly for promastigote of Leishmania amazonensis and epimastigote of Trypanosoma cruzi All compounds showed good activity while nitro compounds 2i and 2k showed inhibition activity at a few μM
- Ud Din, Zia,Fill, Taicia Pacheco,De Assis, Francisco Favaro,Lazarin-Bidóia, Danielle,Kaplum, Vanessa,Garcia, Francielle Pelegrin,Nakamura, Celso Vataru,De Oliveira, Kleber Thiago,Rodrigues-Filho, Edson
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p. 1121 - 1127
(2014/02/14)
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- Substrate scope and synthetic applications of the enantioselective reduction of α-alkyl-β-arylenones mediated by Old Yellow Enzymes
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The ene-reductases mediated bioreduction of a selection of open-chain α-alkyl-β-aryl enones afforded the corresponding saturated α-chiral ketones in high yield and optical purity in several cases. The stereo-electronic requirements of the reaction have been investigated, considering the nature and location of substituents on the aromatic ring as well as the steric hindrance at the α-position and adjacent to the carbonyl functionality. The general considerations drawn allow us to guide the design of α,β-unsaturated ketones to be employed as substrates of ene-reductases in future preparative applications. An interesting case of orthogonality between enzyme-based and substrate-based stereocontrol within the highly homologous ene-reductases from Saccharomyces species (OYE1-3) has been reported and rationalized with the help of computational docking studies. Furthermore, to demonstrate the synthetic versatility of the reaction, the key chiral precursors of biologically active compounds such as (2′R)- stenusines and (S)-iopanoic acid were obtained. The very robust protocol allowed us to run the reactions on preparative scale in quantitative yields, with a simple work-up and no chromatographic purification steps. The Royal Society of Chemistry 2013.
- Brenna, Elisabetta,Cosi, Sara Lucia,Ferrandi, Erica Elisa,Gatti, Francesco G.,Monti, Daniela,Parmeggiani, Fabio,Sacchetti, Alessandro
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supporting information
p. 2988 - 2996
(2013/07/25)
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- Part I: The development of the catalytic wittig reaction
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We have developed the first catalytic (in phosphane) Wittig reaction (CWR). The utilization of an organosilane was pivotal for success as it allowed for the chemoselective reduction of a phosphane oxide. Protocol optimization evaluated the phosphane oxide precatalyst structure, loading, organosilane, temperature, solvent, and base. These studies demonstrated that to maintain viable catalytic performance it was necessary to employ cyclic phosphane oxide precatalysts of type 1. Initial substrate studies utilized sodium carbonate as a base, and further experimentation identified N,N-diisopropylethylamine (DIPEA) as a soluble alternative. The use of DIPEA improved the ease of use, broadened the substrate scope, and decreased the precatalyst loading. The optimized protocols were compatible with alkyl, aryl, and heterocyclic (furyl, indolyl, pyridyl, pyrrolyl, and thienyl) aldehydes to produce both di- and trisubstituted olefins in moderate-to-high yields (60-96 %) by using a precatalyst loading of 4-10 mol %. Kinetic E/Z selectivity was generally 66:34; complete E selectivity for disubstituted α,β-unsaturated products was achieved through a phosphane-mediated isomerization event. The CWR was applied to the synthesis of 54, a known precursor to the anti-Alzheimer drug donepezil hydrochloride, on a multigram scale (12.2 g, 74 % yield). In addition, to our knowledge, the described CWR is the only transition-/heavy-metal-free catalytic olefination process, excluding proton-catalyzed elimination reactions. A point of difference: By utilizing an organosilane to chemoselectively reduce a phosphane oxide precatalyst to a phosphane (see scheme), the first catalytic (in phosphane) Wittig reaction has been developed. The methodology has been applied to the synthesis of 22 disubstituted and 24 trisubstituted olefins, including a multigram synthesis of a precursor to the anti-Alzheimer drug donepezil hydrochloride.
- O'Brien, Christopher J.,Nixon, Zachary S.,Holohan, Andrew J.,Kunkel, Stephen R.,Tellez, Jennifer L.,Doonan, Bryan J.,Coyle, Emma E.,Lavigne, Florie,Kang, Lauren J.,Przeworski, Katherine C.
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supporting information
p. 15281 - 15289
(2013/11/06)
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- Synthesis of β-fluoroenones and their reductive rearrangement in aqueous media
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In this paper, a simple and efficient preparation of β-fluoroenones, as a mixture of E/Z isomers with the E-isomer as the main product, from 1,2-allenic ketones by using TBAF·3H2O in water as a nucleophilic fluorination agent has been developed. Moreover, in exploring the synthetic applications of β-fluoroenones, an unprecedented reductive defluorination rearrangement of β-fluoroenones toward enones under mild conditions in aqueous media was also discovered.
- He, Yan,Shen, Nana,Fan, Xuesen,Zhang, Xinying
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p. 8818 - 8823
(2013/09/23)
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- Rhodium(III)-catalyzed synthesis of pyridines from α,β- unsaturated ketoximes and internal alkynes
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A method for the synthesis of highly substituted pyri-dines from ,-unsaturated oximes and internal alkynes has been developed using [Cp*RhCl2]2-CsOPiv as the catalyst system. The present transformation is carried out by a redox-neutral sequence of vinylic C-H rhodation, alkyne insertion, and C-N bond formation of the putative vinyl rhodium intermediate with the oxime nitrogen, where the N-O bond of oxime derivatives could work as an internal oxidant to maintain the catalytic cycle. Georg Thieme Verlag Stuttgart · New York.
- Too, Pei Chui,Noji, Toshiharu,Lim, Ying Jie,Li, Xingwei,Chiba, Shunsuke
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supporting information; experimental part
p. 2789 - 2794
(2012/01/11)
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- Stereoselective olefination of N-sulfonyl imines with stabilized phosphonium ylides for the synthesis of electron-deficient alkenes
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An unprecedented protocol has been developed for thestereoselective synthesis of structurally diverse electron-deficient alkenes in moderate to excellent yields from readily accessible N-sulfonyl imines and stabilized phosphonium ylides. Significantly, the olefination reaction of N-sulfonylimines with nitrile-stabilized phosphonium ylides affords an array of α,β-unsaturated nitriles with high Z selectivity, and the reactions with ester-, amide-, and ketone-stabilized phosphonium ylides afford α,β-unsaturated esters, amides, and ketones with high E selectivity, respectively. Spectroscopic analysis of the reaction mixtures and trapping of the intermediates allow plausible mechanisms to be proposed. Initialimine/ylide addition leads to the formation of betaines that cyclize to form 1,2-azaphosphetanes that subsequently eliminate iminophosphoranes to yield alkenes. For the synthesis of electron-deficient 1,2-disubstituted alkenes, the presence of an electron-withdrawing group in the betaine allows rapid interconversion between its two diastereomers through proton transfer. The Z/E selectivity for alkene synthesis is determined by the different rates at which the two betaine diastereomers form the corresponding 1,2-azaphosphetane diastereomers. In contrast, the Z/E selectivity for the synthesis of electron-deficient trisubstituted alkenes originates from the diastereoselective addition of stabilized phosphonium ylides to N-sulfonyl imines.
- Fang, Fan,Li, Yuan,Tian, Shi-Kai
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experimental part
p. 1084 - 1091
(2011/04/15)
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- Stereoseleetive synthesis of polysubstituted alkenes through a phosphine-mediated three-component system of aldehydes, α-halo carbonyl compounds, and terminal alkenes
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A study was conducted to demonstrate stereoselective synthesis of polysubstituted alkenes through a phosphine-mediated three-component system of aldehydes, α-halo carbonyl compounds, and terminal alkenes. Triphenylphosphine, α-halo carbonyl compounds, and methyl acrylate were added to a solution of aldehyde in chloroform or 1-propanol under nitrogen at room temperature. The resulting mixture was stirred at the specified temperature until transformation was completely observed by thin layer chromatography (TLC) analysis. The mixture was cooled to room temperature and purified by column chromatography on silica gel, eluting with petroleum ether/ethyl acetate. The study demonstrated that the first one-pot and three-component reaction of aldehydes, α-haloacetates, and terminal alkenes was developed in the presence of phenylphosphine to produce a wide range of trisubstituted alkenes with significant stereoselectivity.
- Liu, Da-Neng,Tian, Shi-Kai
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supporting information; experimental part
p. 4538 - 4542
(2009/12/25)
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- The palladium-catalyzed aerobic kinetic resolution of secondary alcohols: Reaction development, scope, and applications
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The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23°C, resulting in enhanced catalyst selectivity. These improved reaction conditions have permitted the successful kinetic resolution of benzylic, allylic, and cyclopropyl secondary alcohols to high enantiomeric excess with good-toexcellent selectivity factors. This catalyst system has also been applied to the desymmetrization of meso-diols, providing high yields of enantioenriched hydroxyketones.
- Ebner, David C.,Bagdanoff, Jeffrey T.,Ferreira, Eric M.,McFadden, Ryan M.,Caspi, Daniel D.,Trend, Raissa M.,Stoltz, Brian M.
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supporting information; experimental part
p. 12978 - 12992
(2010/06/19)
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- Highly enantioselective synthesis of optically active ketones by iridium-catalyzed asymmetric hydrogenation
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(Chemical Equation Presented) Close to perfect enantioselectivity (up to 99% ee, see scheme) is found for the formation of α-substituted ketones by the asymmetric hydrogenation of enones with an iridium-phosphinooxazoline catalyst. In an operationally simple process, both linear and cyclic substrates react well and afford the desired products in high yields. A wide variety of substituents are tolerated, thus making the method synthetically appealing.
- Lu, Sheng-Mei,Bolm, Carsten
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supporting information; experimental part
p. 8920 - 8923
(2009/05/30)
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- Axially chiral NHC-Pd(II) complexes in the oxidative kinetic resolution of secondary alcohols using molecular oxygen as a terminal oxidant
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(Chemical Equation Presented) Axially chiral N-heterocyclic carbene (NHC) Pd(II) complexes were prepared from optically active 1,1′-binaphthalenyl- 2,2′-diamine (BINAM) and H8-BINAM and applied in the oxidative kinetic resolution of secondary alcohols using molecular oxygen as a terminal oxidant. The corresponding sec-alcohols can be obtained in good yields with moderate to good enantioselectivities.
- Chen, Tao,Jiang, Jia-Jun,Xu, Qin,Shi, Min
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p. 865 - 868
(2007/10/03)
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- A new approach to the Nazarov reaction via sequential electrocyclic ring opening and ring closure
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Regioselective dichlorocyclopropanation of 2-silyloxydienes furnishes vinylcyclopropanol silyl ethers in good yield. Treatment with silver(I) at room temperature effects disrotatory electrocyclic opening to a 2-chloro-3-silyloxypentadienyl cation, which then undergoes conrotatory (Nazarov) electrocyclization to provide chlorocyclopentenones. This two-step sequence offers a convenient and mild alternative to the standard Nazarov cyclization protocol via a formal 4+1 construction and furnishes products containing useful halogen functionality. In one case possessing a pendant phenyl group, interrupted Nazarov reaction to give a benzohydrindenone was observed. Copyright
- Grant, Tina N.,West
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p. 9348 - 9349
(2007/10/03)
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- Ring expansion/homologation-aldehyde condensation cascade using tert-trihalomethylcarbinols
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Treatment of cyclic tert-trihalomethylcarbinols with CrCl2 in THF/HMPA in the presence of aryl or aliphatic aldehydes initiates a cascade sequence of one carbon ring expansion-olefination affording conjugated exocyclic ketones. Acyclic tert-trihalomethylcarbinols undergo a comparable cascade of one carbon homologation-olefination.
- Falck,He, Anyu,Manmohan Reddy,Kundu, Abhijit,Barma, Deb K.,Bandyopadhyay,Kamila, Sukanta,Akella, Radha,Bejot, Romain,Mioskowski, Charles
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p. 4645 - 4647
(2007/10/03)
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- Aldol condensations of aldehydes and ketones catalyzed by rare earth(III) perfluorooctane sulfonates in fluorous solvents
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Rare earth(III) perfluorooctane sulfonates (RE(OPf)3) catalyze the efficient aldol condensation of different ketones with various aromatic aldehydes in fluorous solvents without the occurrence of any self-condensations. By simple separation of the fluorous phase containing only catalyst, reaction can be repeated several times.
- Yi, Wen-Bin,Cai, Chun
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p. 1553 - 1558
(2007/10/03)
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- Palladium-Catalyzed Oxidative Kinetic Resolution with Ambient Air as the Stoichiometric Oxidation Gas
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Air is enough to mediate the highly enantioselective oxidation of secondary alcohols at room temperature with palladium(II) and sparteine in nonflammable solvents. Examination of the role of solvents capable of hydrogen bonding and their ability to solvate halide anions led to a novel set of conditions for the highly enantioselective oxidative kinetic resolution of secondary alcohols.
- Bagdanoff, Jeffrey T.,Stoltz, Brian M.
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p. 353 - 357
(2007/10/03)
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- Palladium-catalyzed aerobic oxidative kinetic resolution of alcohols with an achiral exogenous base
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Substitution of exogenous (-)-sparteine for a more practical achiral base in the aerobic oxidative kinetic resolution of secondary alcohols is described. Carbonate bases are the most effective of those screened and allow for effective kinetic resolution of benzylic, allylic, and aliphatic substrates. The procedure was also successfully extended to the oxidative desymmetrization of meso diols.
- Mandal, Sunil K.,Sigman, Matthew S.
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p. 7535 - 7537
(2007/10/03)
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- Direct preparation of monoarylidene derivatives of aldehydes and enolizable ketones with DIMCARB
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(Matrix presented) Aryl α,β-unsaturated ketones and aldehydes were synthesized, in moderate to excellent yields, with use of dimethylammonium dimethyl carbamate (DIMCARB) as a recyclable reaction medium and as a catalyst.
- Kreher, Ulf P.,Rosamilia, Anthony E.,Raston, Colin L.,Scott, Janet L.,Strauss, Christopher R.
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p. 3107 - 3110
(2007/10/03)
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- Scope of enantioselective Palladium(II)-catalyzed aerobic alcohol oxidations with (-)-sparteine
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Evaluation of the substrate scope for Pd(II)/ (-)-sparteine catalyzed aerobic oxidative kinetic resolution of secondary alcohols is disclosed. An improved system is found with use of tert-butyl alcohol solvent in which benzylic and aliphatic alcohols as well as alcohols containing olefins are effectively oxidatively resolved. For substrates that successfully undergo oxidative kinetic resolution, krel values are generally between 10 and 20. Successful scale-up of various substrates to 10-mmol scale is described. Extension to oxidative desymmetrization of 1,3-meso-diols is successful with enantiomeric excesses ranging from 78 to 85%.
- Mandal, Sunil K.,Jensen, David R.,Pugsley, Jacob S.,Sigman, Matthew S.
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p. 4600 - 4603
(2007/10/03)
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- Palladium-catalyzed enantioselective oxidation of alcohols: a dramatic rate acceleration by Cs2CO3/t-BuOH.
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[reaction: see text] The addition of Cs(2)CO(3) and t-BuOH provides a dramatic rate acceleration in the palladium-catalyzed aerobic oxidative kinetic resolution of secondary alcohols while maintaining the selectivity of the process.
- Bagdanoff, Jeffrey T,Ferreira, Eric M,Stoltz, Brian M
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p. 835 - 837
(2007/10/03)
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- Double Michael addition reactions of some new 1,5-diaryl-2-alkyl-1,4-pentadien-3-ones: Part II
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The reactivity of unsymmetrical 1,5-diaryl-2-alkyl-l,4-pentadien-3-ones with active methylene compounds has been studied. The structures of the compounds have been established by spectral parameters.
- Padmavathi,Ramana Reddy,Venugopal Reddy,Audisesha Reddy,Bhaskar Reddy
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p. 667 - 673
(2007/10/03)
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- Selective intermolecular coupling of alkynes with nitriles and ketones via ββ′ carbon-carbon bond cleavage of zirconacyclopentenes
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Selective intermolecular coupling of alkynes with nitriles and ketones was performed by the reaction of a mixture of alkynes and Cp2ZrEt2 with nitriles and ketones, respectively. Hydrolysis of the mixture gave α,β-unsaturated ketones and allylic alcohols in good to excellent yields, respectively. These reactions proceeded via zirconacyclopentenes which were prepared by the reaction of alkynes with Cp2ZrEt2. The structure of zirconacyclopentene, which was prepared from diphenylacetylene and Cp2ZrEt2, was determined by X-ray analysis. It clearly indicated that there is a single bond between the β- and β′-carbons of the zirconacyclopentene. The reaction of zirconacyclopentenes with nitriles or ketones proceeded via the β,β′ carbon-carbon bond cleavage of the zirconacyclopentenes. In a similar way, addition of PMes to the zirconacyclopentene afforded a zirconocenealkyne complex in 87% yield.
- Takahashi, Tamotsu,Xi, Chanjuan,Xi, Zhenfeng,Kageyama, Motohiro,Fischer, Reinald,Nakajima, Kiyohiko,Negishi, Ei-Ichi
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p. 6802 - 6806
(2007/10/03)
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- Stereochemical control in microbial reduction. XXVIII. Asymmetric reduction of α,β-unsaturated ketones with Bakers' yeast
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Bakers' yeast reduction of α,β-unsaturated ketones affords optically active saturated ketones contaminated by allylic and saturated alcohols as minor components. Stereoselectivity of the reduction of carbon-carbon double bond strongly depends on the structure of β-aryl substituent. The bakers' yeast reduction of β-phenyl enones gives saturated ketones in moderate stereoselectivity. Stereoselectivity is not altered by substitution at the para-position, whereas introduction of a substituent at the ortho- or meta-position drastically improves the stereoselectivity. Deuterium-labeling experiments reveal that the enzymatic reduction of carbon-carbon double bond proceeds with formal trans-addition of hydrogens regardless the efficiency of stereoselectivity. The resulting optically active ketone was converted to the precursor of (S)-iopanoic acid, an inhibitor of thyroxine 5′-deiodinase that is a thyroid hormone-converting enzyme and an oral cholecystographic agent.
- Kawai, Yasushi,Saitou, Kentarou,Hida, Kouichi,Dao, Duc Hai,Ohno, Atsuyoshi
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p. 2633 - 2638
(2007/10/03)
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- Asymmetric Reduction of α,β-Unsaturated Ketones with Bakers' Yeast
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Bakers' yeast reduction of 3-methyl-4-phenyl-3-buten-2-one affords the corresponding saturated (3S)-ketone selectively, while 4-(2-furyl)-3-methyl-3-buten-2-one is selectively transformed to the corresponding (2S)-allylic alcohol.
- Kawai, Yasushi,Saitou, Kentarou,Hida, Kouichi,Ohno, Atsuyoshi
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p. 2143 - 2144
(2007/10/03)
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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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- An Expedient Synthesis of α,β-Unsaturated Ketones Using Nitroalkenes and Sulfones
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A facile synthesis of various substituted α,β-unsaturated ketones utilizing nitroalkenes and sulfones are described, in which conjugate addition of sulfonyl carbanions to nitroalkenes, ozonolysis or acid treatment of the resulting lithium nitronates and subsequent elimination of sulfinic acid from keto sulfones by DBU are involved.
- Awen, Bahlul Z.,Miyashita, Masaaki,Shiratani, Tomonori,Yoshikoshi, Akira,Irie, Hiroshi
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p. 767 - 768
(2007/10/02)
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- Interaction of Fischer carbene complexes of the type W(CO)5[C(OMe)R] (R = CH3, C2H5) with acetylenes
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W(CO)5[C(OMe)CH2R1] (R1 = H, CH3) reacts with PhC2R2 (R2 = Ph, CH3) in toluene at 100°C to give vinyl ethers and enones. The formation of these products can be explained by an exocyclic β-hydride elimination reaction of a metallacyclobutene intermediate.
- Macomber, David W.
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p. 1589 - 1591
(2008/10/08)
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- INSERTION D'ALLENES. VIII. FORMATION DE CETONES α,β-INSATUREES PAR HYDROACYLATION D'ALLENES EN PRESENCE DE TETRACARBONYL FERRATE DE SODIUM
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α,β-Unsaturated ketones are generated in moderate yields (50-60percent) from allene or a mono-, di- or tri-substituted allenic hydrocarbon, an alkyl halide and sodium tetracarbonylferrate.The first step is the formation of a complex anion which results from transfer of the alkyl group on a coordinated CO, then of the acyl ligand thus formed on the allenic sp carbon.Protonation with acetic acid yields a hydroxy-η4-trimethylenemethane, easily isomerised into an η4-heterodieneiron tricarbonyl.Finally, the α,β-unsaturated ketone is released upon oxidation with trimethylamine oxide.The most substituted ketone predominates.
- Roustan, J. L.,Guinot, A.,Cadiot, P.
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p. 367 - 378
(2007/10/02)
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