- Asymmetric Synthesis of 2,3-Disubstituted Cyclic Ketones by Enantioselective Conjugate Radical Additions
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Enantioselective conjugate radical addition to 2-acyloxymethyl cycloalkenones proceeds in high yield with outstanding diastereoselectivity and excellent enantioselectivity using chiral salen Lewis acids. The process provides access to 2,3-disubstituted cycloalkanones, a structural motif present in natural products.
- Nad, Sukanya,Sibi, Mukund P.
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Read Online
- CONJUGATE ADDITIONS TO α,β-UNSATURATED CARBONYL COMPOUNDS IN AQUEOUS MEDIA
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Alkyl halides in the presence of zinc copper couple add smoothly to α-enones and α-enals in aqueous solvents.Sonication enhances the efficiency of the process, which leads to the conjugate adducts in high yields.The reaction follows most probably a radical pathway, and can be used for the addition of functionalized groups.
- Petrier, C.,Dupuy, C.,Luche, J. L.
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Read Online
- Deciphering Reactivity and Selectivity Patterns in Aliphatic C-H Bond Oxygenation of Cyclopentane and Cyclohexane Derivatives
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A kinetic, product, and computational study on the reactions of the cumyloxyl radical with monosubstituted cyclopentanes and cyclohexanes has been carried out. HAT rates, site-selectivities for C-H bond oxidation, and DFT computations provide quantitative information and theoretical models to explain the observed patterns. Cyclopentanes functionalize predominantly at C-1, and tertiary C-H bond activation barriers decrease on going from methyl- and tert-butylcyclopentane to phenylcyclopentane, in line with the computed C-H BDEs. With cyclohexanes, the relative importance of HAT from C-1 decreases on going from methyl- and phenylcyclohexane to ethyl-, isopropyl-, and tert-butylcyclohexane. Deactivation is also observed at C-2 with site-selectivity that progressively shifts to C-3 and C-4 with increasing substituent steric bulk. The site-selectivities observed in the corresponding oxidations promoted by ethyl(trifluoromethyl)dioxirane support this mechanistic picture. Comparison of these results with those obtained previously for C-H bond azidation and functionalizations promoted by the PINO radical of phenyl and tert-butylcyclohexane, together with new calculations, provides a mechanistic framework for understanding C-H bond functionalization of cycloalkanes. The nature of the HAT reagent, C-H bond strengths, and torsional effects are important determinants of site-selectivity, with the latter effects that play a major role in the reactions of oxygen-centered HAT reagents with monosubstituted cyclohexanes.
- Martin, Teo,Galeotti, Marco,Salamone, Michela,Liu, Fengjiao,Yu, Yanmin,Duan, Meng,Houk,Bietti, Massimo
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supporting information
p. 9925 - 9937
(2021/06/30)
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- Counterion Enhanced Organocatalysis: A Novel Approach for the Asymmetric Transfer Hydrogenation of Enones
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We present a novel strategy for organocatalytic transfer hydrogenations relying on an ion-paired catalyst of natural l-amino acids as main source of chirality in combination with racemic, atropisomeric phosphoric acids as counteranion. The combination of a chiral cation with a structurally flexible anion resulted in a novel chiral framework for asymmetric transfer hydrogenations with enhanced selectivity through synergistic effects. The optimized catalytic system, in combination with a Hantzsch ester as hydrogen source for biomimetic transfer hydrogenation, enabled high enantioselectivity and excellent yields for a series of α,β-unsaturated cyclohexenones under mild conditions. Moreover, owing to the use of readily available and chiral pool-derived building blocks, it could be prepared in a straightforward and significantly cheaper way compared to the current state of the art.
- Scharinger, Fabian,Márk Pálv?lgyi, ádám,Zeindlhofer, Veronika,Schnürch, Michael,Schr?der, Christian,Bica-Schr?der, Katharina
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p. 3776 - 3782
(2020/06/22)
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- Stereochemical Insights into the Anaerobic Degradation of 4-Isopropylbenzoyl-CoA in the Denitrifying Bacterium Strain pCyN1
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The constitutions and absolute configurations of two previously unknown intermediates, (1S,2S,4S)-2-hydroxy-4-isopropylcyclohexane-1-carboxylate and (S)-3-isopropylpimelate, of anaerobic degradation of p-cymene in the bacterium Aromatoleum aromaticum pCyN
- Küppers, Julian,Becker, Patrick,Jarling, René,D?rries, Marvin,Caki?, Nevenka,Schmidtmann, Marc,Christoffers, Jens,Rabus, Ralf,Wilkes, Heinz
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supporting information
p. 4722 - 4731
(2019/03/13)
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- Readily Accessible Bulky Iron Catalysts exhibiting Site Selectivity in the Oxidation of Steroidal Substrates
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Bulky iron complexes are described that catalyze the site-selective oxidation of alkyl C-H bonds with hydrogen peroxide under mild conditions. Steric bulk at the iron center is introduced by appending trialkylsilyl groups at the meta-position of the pyridines in tetradentate aminopyridine ligands, and this effect translates into high product yields, an enhanced preferential oxidation of secondary over tertiary C-H bonds, and the ability to perform site-selective oxidation of methylenic sites in terpenoid and steroidal substrates. Unprecedented site selective oxidation at C6 and C12 methylenic sites in steroidal substrates is shown to be governed by the chirality of the catalysts.
- Font, David,Canta, Mercè,Milan, Michela,Cussó, Olaf,Ribas, Xavi,Klein Gebbink, Robertus J. M.,Costas, Miquel
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supporting information
p. 5776 - 5779
(2016/05/09)
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- Pichia stipitis OYE 2.6 variants with improved catalytic efficiencies from site-saturation mutagenesis libraries
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An earlier directed evolution project using alkene reductase OYE 2.6 from Pichia stipitis yielded 13 active site variants with improved properties toward three homologous Baylis-Hillman adducts. Here, we probed the generality of these improvements by testing the wild-type and all 13 variants against a panel of 16 structurally-diverse electron-deficient alkenes. Several substrates were sterically demanding, and as hoped, creating additional active site volume yielded better conversions for these alkenes. The most impressive improvement was found for 2-butylidenecyclohexanone. The wild-type provided less than 20% conversion after 24 h; a triple mutant afforded more than 60% conversion in the same time period. Moreover, even wild-type OYE 2.6 can reduce cyclohexenones with very bulky 4-substituents efficiently.
- Patterson-Orazem, Athéna,Sullivan, Bradford,Stewart, Jon D.
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p. 5628 - 5632
(2015/01/09)
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- Site-selective oxidation of unactivated C sp 3-H bonds with hypervalent iodine(III) reagents
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By design: The site-selective oxidation of unactivated secondary C sp 3-H bonds was accomplished with hypervalent iodine(III) reagents and tert-butyl hydroperoxide (see scheme). The preparation and derivatization of the hypervalent iodine(III) reagent are simple, thus allowing the rational design of these reagents to optimize the site selectivity of the oxidation. Copyright
- Moteki, Shin A.,Usui, Asuka,Zhang, Tiexin,Solorio Alvarado, Cesar R.,Maruoka, Keiji
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supporting information
p. 8657 - 8660
(2013/09/12)
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- Catalytic enantioselective conjugate addition of Grignard reagents to cyclic enones using C1-1,1′-bisisoquinoline-based chiral ligands
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New highly constrained chiral C1-1,1′-bisisoquinoline ligands were examined in the enantioselective conjugate addition of Grignard reagents to cyclohexenone and cyclopentenone. The desired 1,4-adducts were obtained in excellent yield and moderate enantiomeric excess (up to 35%). Copyright Taylor & Francis Group, LLC.
- Qi, Gao,Judeh, Zaher M.A.
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experimental part
p. 1585 - 1592
(2012/05/04)
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- Preparation and characterization of new C2- and C 1-symmetric nitrogen, oxygen, phosphorous, and sulfur derivatives and analogs of TADDOL. part i
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The chloro alcohols 4-6 derived from TADDOLs (=α,α, α′,α′-tetraaryl-1,3-dioxolan-4,5-dimethanols) are used to prepare corresponding sulfanyl alcohols, ethers, and amines (Scheme 1 and Table 1). The dithiol analog of TADDOL and derivatives thereof, 45-49,
- Pichota, Arkadius,Gramlich, Volker,Beck, Albert K.,Seebach, Dieter
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experimental part
p. 1239 - 1272
(2012/09/21)
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- Synthesis and AChE inhibitory activity of new chiral tetrahydroacridine analogues from terpenic cyclanones
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This work describes the enantioselective synthesis of a new series of terpenic chiral 9-aminotetrahydroacridine analogues. Several chiral ketones were synthesized from natural monoterpenes in an optically active form and subjected to the cyclodehydration reactions with anthranilonitrile in the presence of BF3·Et2O as catalyst. The 9-aminotetrahydroacridine analogues were tested as acetylcholinesterase (AChE) inhibitors. Based on qualitative structure-activity relationship some trends are suggested.
- Santos Pisoni, Diego dos,Sobieski da Costa, Jessé,Gamba, Douglas,Petzhold, Cesar Liberato,César de Amorim Borges, Antonio,Ceschi, Marco Antonio,Lunardi, Paula,Saraiva Gon?alves, Carlos Alberto
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scheme or table
p. 526 - 535
(2010/04/06)
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- Indium/copper-mediated conjugate addition of unactivated alkyl iodides to α,β-unsaturated carbonyl compounds in water
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An efficient method for the conjugate addition of unactivated alkyl iodides to α,β-unsaturated carbonyl compounds using indium/copper in water is described. The reactions proceed more efficiently in water than in organic solvents. In, CuI, and InCl3
- Shen, Zhi-Liang,Cheong, Hao-Lun,Loh, Teck-Peng
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supporting information; scheme or table
p. 1051 - 1054
(2009/05/27)
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- Highly enantio- and s-trans C=C bond selective catalytic hydrogenation of cyclic enones: Alternative synthesis of (-)-menthol
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A highly enantioselective catalytic hydrogenation of cyclic enones was achieved by using the combination of a cationic Rh1 complex, (S)-5,5′-bis{di(3,5-di-tert-butyl-4-methoxyphenylphosphino)}-4, 4′-bi-1,3-benzodioxole (DTBM-SEGPHOS), and (CH2CH 2PPh3Br)2. The presence of an s-cis C=C bond isopropylidene moiety on the cyclic enone influenced the enantioselectivity of the hydrogenation. Thus, the hydrogenation of 3-alkyl-6-isopropylidene-2- cyclohexen-1-one, which contains both s-cis and s-trans enones, proceeded in excellent enantioselectivity (up to 98% ee). To obtain high enantio- and s-trans selectivities, the addition of a halogen source to the cationic Rh complex was the essential step. With the key step of the s-trans selective asymmetric hydrogenation of piperitenone, we demonstrated a new synthetic method for optically pure (-)-menthol via three atom-economical hydrogenations. Moreover, we found that the complete s-trans and s-cis C=C bond selective reactions were also realized by the proper choice of both the chiral ligands and halides.
- Ohshima, Takashi,Tadaoka, Hiroshi,Hori, Kiyoto,Sayo, Noboru,Mashima, Kazushi
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scheme or table
p. 2060 - 2066
(2009/04/07)
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- General method for the expedient synthesis of salt-free diorganozinc reagents using zinc methoxide
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The effect of counterions has a great impact on the solubility of magnesium salts in Et2O. By reacting Zn(OMe)2 with readily available Grignard reagents, it was possible to induce the complete precipitation of magnesium salts and then obtain salt-free dio
- Cote, Alexandre,Charette, Andre B.
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p. 2771 - 2773
(2008/10/09)
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- Enantioselective Cu-catalyzed 1,4-addition of Grignard reagents to cyclohexenone using Taddol-derived phosphine-phosphite ligands and 2-methyl-THF as a solvent
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A small library of modular P,P ligands was screened and a potent Cu-based catalyst system was identified for highly enantioselective 1,4-additions to cyclohexenone with an unprecedented broad spectrum of Grignard reagents. Surprisingly, the highest selectivities were achieved in most cases in 2-methyl-THF, a green solvent underestimated so far.
- Robert, Tobias,Velder, Janna,Schmalz, Hans-Guenther
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supporting information; experimental part
p. 7718 - 7721
(2009/04/10)
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- METHODS FOR PREPARING DIORGANOZINC COMPOUNDS
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There are provided methods for preparing the diorganozmc compounds of formula R2Zn (I or Ia), where R is a defined organic radical, and the two R groups can be the same or different The starting material is the zinc compound ZnX2 (II) or R2ZnX (IIa), where X is a defined anion and R2 is a defined organic radical. The zinc reagent of type II is combined with a Grignard reagent and also, when X is Cl or Br, with an alkali metal reagent (VI) to form the diorganozinc product (I or Ia). Also provided are methods for preparing the zinc alcoholates of formula Zn(OR1)2 by reaction of ZnX2, where X = Cl or Br, with an alkali metal reagent of the formula MOR1, where M = Na or K, and where R1 is a defined organic radical.
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Page/Page column 19-20
(2009/01/20)
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- Chiral phosphinoazomethinylate salts as new 'one-step available' ligands for copper-catalyzed asymmetric conjugate addition
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Herein, we report the use of phosphinoazomethinylate salts as chiral efficient ligands for the copper-catalyzed asymmetric conjugate addition (ACA) of dialkylzinc to various enones. These tridentate P,N,O ligands are straightforwardly obtained in a one-step procedure from commercially available enantiopure α-aminoacids. Performing the conjugate addition in the greener AcOEt solvent, high enantioselectivities were reached for both cyclic and acyclic enones ranging between 72% to 98% ee and 96% to >99%, respectively. The 2/1 Cu/ligand ratio required to obtain high enantioselectivities, led us to envisage a copper-copper bi-metallic catalytic system for this transformation.
- Wencel, Joanna,Rix, Diane,Jennequin, Thomas,Labat, Stephane,Crevisy, Christophe,Mauduit, Marc
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p. 1804 - 1809
(2008/12/21)
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- Highly enantioselective transfer hydrogenation of α,β- unsaturated ketones
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We describe an efficient and highly enantioselective conjugate transfer hydrogenation of α,β-unsaturated ketones that is catalyzed by a salt made from tert-butyl valinate and a recently introduced powerful chiral phosphoric acid catalyst (TRIP). Copyright
- Martin, Nolwenn J. A.,List, Benjamin
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p. 13368 - 13369
(2007/10/03)
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- New bidentate alkoxy-NHC ligands for enantioselective copper-catalysed conjugate addition
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Chiral alkoxy-imidazolinium salts are easily available via a five-step procedure starting from β-aminoalcohols. This new family of alkoxy-N-heterocyclic carbene (NHC) precursors is shown to be highly active in the enantioselective copper-catalysed conjugate addition to cyclic enones. Complete conversion with low catalyst loading and good enantiomeric excesses up to 93% were obtained at room temperature.
- Clavier, Herve,Coutable, Ludovic,Guillemin, Jean-Claude,Mauduit, Marc
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p. 921 - 924
(2007/10/03)
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- Design and synthesis of new bidentate alkoxy-NHC ligands for enantioselective copper-catalyzed conjugate addition
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A new family of chiral alkoxy-N-heterocyclic carbene (NHC) ligands has been designed for the enantioselective copper-catalyzed conjugate addition of dialkylzincs to enones. These new bidentate NHC ligands were synthesized in high overall yields using a five-step procedure starting from commercially available β-aminoalcohols. Influence of the temperature, base, solvent and copper source were studied in order to optimize the stereoselectivity of the addition. High reactivity and excellent enantioselectivity were obtained at ambient temperature with a range of cyclic enones and dialkylzinc. Addition to acyclic enones has also been studied.
- Clavier, Hervé,Coutable, Ludovic,Toupet, Lo?c,Guillemin, Jean-Claude,Mauduit, Marc
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p. 5237 - 5254
(2007/10/03)
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- Assessing the Substrate Selectivities and Enantioselectivities of Eight Novel Baeyer-Villiger Monooxygenases toward Alkyl-Substituted Cyclohexanones
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Genes encoding eight Baeyer-Villiger monooxygenases have recently been cloned from bacteria inhabiting a wastewater treatment plant. We have carried out a systematic investigation in which each newly cloned enzyme, as well as the cyclohexanone monooxygenase from Acinetobacter sp. NCIB 9871, was used to oxidize 15 different alkyl-substituted cyclohexanones. The panel of substrates included equal numbers of 2-, 3-, and 4-alkyl-substituted compounds to probe each enzyme's stereoselectivity toward a homologous series of synthetically important compounds. For all 4-alkyl-substituted cyclohexanones tested, enzymes were discovered that afforded each of the corresponding (S)-lactones in ≥98% ee. This was also true for the 2-alkyl-substituted cyclohexanones examined. The situation was more complex for 3-akyl-substituted cyclohexanones. In a few cases, single Baeyer-Villiger monooxygenases possessed both high regio- and enantioselectivities toward these compounds. More commonly, however, they showed only one type of selectivity. Nonetheless, enzymes with such properties might be useful as parts of a two-step bioprocess where an initial kinetic resolution is followed by a regioselective oxidation on the isolated, optically pure ketone.
- Kyte, Brian G.,Rouviere, Pierre,Cheng, Qiong,Stewart, Jon D.
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- Triethylaluminum- or triethylborane-induced free radical reaction of alkyl iodides and α,β-unsaturated compounds
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A series of α,β-unsaturated compounds, 1a-c, 9, 13, and 17, were used as reactants in free radical conjugate addition reactions with different radicals generated from alkyl iodides such as 3, 4, or 5 in the presence of triethylborane-oxygen in air or via the use of triethylaluminum-benzoyl peroxide as a free radical initiator. When the reactions were carried out using triethylborane-air, the products, in most cases, were clean and were easily purified. However, higher yields of the 1,4-adducts and less side reactions occurred when less reactive substrates were used as Michael acceptors in reactions with triethylaluminum-benzoyl peroxide and alkyl iodide under similar conditions. A mechanism for this is proposed in Scheme 1.
- Liu, Jing-Yuan,Jang, Yoeng-Jiunn,Lin, Wen-Wei,Liu, Ju-Tsung,Yao, Ching-Fa
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p. 4030 - 4038
(2007/10/03)
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- Highly practical and enantioselective Cu-catalyzed conjugate addition of alkylzinc reagents to cyclic enones at ambient temperature
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(Matrix presented) A new ligand for Cu-catalyzed enantioselective additions of dialkylzincs to cyclic enones has been developed. In addition to providing good to excellent enantioselectivities with a range of cyclic enones and dialkylzincs, the ligand has several notworthy features: it can be readily prepared in just two steps, is an air-stable crystalline solid, and provides optimal performance at ambient temperature.
- Krauss, Isaac J.,Leighton, James L.
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p. 3201 - 3203
(2007/10/03)
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- Chiral diselenide ligands for the asymmetric copper-catalyzed conjugate addition of Grignard reagents to enones
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The copper-catalyzed conjugate addition of Grignard reagents to enones in the presence of chiral diselenide oxazoline ligands has been studied and found to provide good yields and useful levels of asymmetric induction.
- Braga, Antonio L,Silva, Sandra J.N,Lüdtke, Diogo S,Drekener, Roberta L,Silveira, Claudio C,Rocha, Joao B.T,Wessjohann, Ludger A
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p. 7329 - 7331
(2007/10/03)
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- Microreaction technology as a novel approach to drug design, process development and reliability
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This paper focuses on the application of microreaction technology in the life science industry. Certain features of microreaction technology, for example, mixing, heat transfer, and residence time distribution, are discussed. Important advantages such as high operational safety and the possibility to transfer the experimental results directly from laboratory to the production of pilot-plant scales are mentioned. Potential application fields in the drug discovery and development processes, from research to production, by including chemical synthesis of different targets in the case of the quinoline acid derivative (ciprofloxacin) and the Paal - Knorr pyrrole synthesis are presented.
- Taghavi-Moghadam, Shahriyar,Kleemann, Axel,Golbig, Klaus Georg
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p. 652 - 658
(2013/09/07)
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- Diethylzinc: A chain-transfer agent in intermolecular radical additions. A parallel with triethylborane
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In the presence of oxygen, diethylzinc can be used to promote radical additions to C=N bond containing radical acceptors and to enones. In these reactions, it plays at the same time the role of the initiator and the role of the chain-transfer reagent. A p
- Bertrand, Michele P.,Feray, Laurence,Nouguier, Robert,Perfetti
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p. 9189 - 9193
(2007/10/03)
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- Selectivity in Organic Group Transfer in Reactions of Mixed Diorganomanganese(II) and Triorganomanganate(II) with 2-Cyclohexen-1-one or Cyclohexanecarbaldehyde
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The unsymmetrical diorganomanganeses(II) (R1R2Mn) and magnesium triorganomanganates(II) (R21R2MnMgX) reacted with 2-cyclohexen-1-one to produce the 1,4-addition products in moderate to good yields. The approximate reactivity order obtained from the product distribution was CH2=CHCH2 > PhS > n-Bu > Ph > Me, Me3SiCH2, n-C6H13-CΞC. In contrast, the reactivity order for the addition of these reagents to cyclohexanecarbaldehyde was CH2=CHCH2 > Ph > Me > n-Bu > n-C6H13CΞC > Me3SiCH2.
- Yorimitsu, Hideki,Hayashi, Yasuhiro,Tang, Jun,Shinokubo, Hiroshi,Oshima, Koichiro
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p. 2297 - 2300
(2007/10/03)
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- Highly Diastereoselective Intermolecular β-Addition of Alkyl Radicals to Chiral 2-(Arylsulfinyl)-2-cycloalkenones
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The diastereoselectivity of intermolecular β-addition of alkyl radicals to 2-(arylsulfinyl)-2-cycloalkenones depends largely upon the structure of the arylsulfinyl group. The reaction of 2-cyclopentenones or 2-cyclohexenones having a sterically bulky arylsulfinyl group such as (3,5-di-tert-butyl-4-methoxyphenyl)sulfinyl, (2,4,6-triisopropylphenyl)sulfinyl or (2,4,6-trimethylphenyl)sulfinyl group gives 3-alkyl-2-(arylsulfinyl)-1-cyclopentanones or 3-alkyl-2-(arylsulfinyl)-1-cyclohexanones in excellent yields and with high diastereoselectivity. Both the X-ray crystallographic analysis and the NOE experiment in the 1H NMR spectrum of (S)-2-[(2,4,6-triisopropylphenyl)sulfinyl]- and (S)-2-[(2,4,6-trimethylphenyl)sulfinyl]-2-cyclopentenone reveal an effective shielding of one of the olefin faces at the β-position by o-isopropyl and o-methyl groups. The addition of bidentate Lewis acids reverses the stereoselection through chelating the intermediates to give the addition products with high diastereoselectivity.
- Mase, Nobuyuki,Watanabe, Yoshihiko,Ueno, Yoshio,Toru, Takeshi
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p. 7794 - 7800
(2007/10/03)
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- Tandem energy transfer-electron transfer in the photosensitized alkylation of α,β-unsaturated ketones
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α,β-Unsaturated ketones are not conveniently alkylated by radicals generated from tetraalkylstannanes via photoinduced electron transfer (PET), either by direct irradiation or when a singlet sensitizer (an aromatic nitrile, a pyrilium salt) is used. However, the procedure is successful with tetramethyl pyromellitate (TMPM) as the sensitizer. TMPM is promoted to the triplet state by energy transfer from the unsaturated ketones and then sensitizes the cleavage of alkylstannanes by electron transfer. The alkyl radicals thus formed finally add to the unsaturated ketones, giving the β-alkyl derivatives.
- Fagnoni, Maurizio,Mella, Mariella,Albini, Angelo
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p. 777 - 780
(2007/10/03)
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- Chiral Mercaptoaryl-oxazolines as Ligands in Enantioselective Copper-Catalyzed 1,4-Additions of Grignard Reagents to Enones
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A series of chiral enantiomerically pure mercaptoaryl-oxazolines has been synthesized.Copper(I) thiolate complexes derived from these ligands proved to be efficient catalysts for the 1,4-addition of Grignard reagents to cyclic enones.Enantioselectivities
- Zhou, Qi-Lin,Pfaltz, Andreas
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p. 4467 - 4478
(2007/10/02)
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- 3-Metallated enamines XI. Transmetallation of 3-Stannylated enamines - A new method to generate 1-aminoallyllithium compounds
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The transmetallation of 3-stannylated enamines, 1-morpholino-3-(trialkylstannyl)cycloalk-1-enes and 3-morpholino-5-(tributylstannyl)hex-3-ene, with butyllithium is a new and general way to generate s1-aminoallyllithium compounds. Stabilization by aromatic substituents is not further necessarily as in the case of preparation by deprotonation and even the thermodynamically less stable exoamino derivatives are accessible. Therefore homoenolate-equivalents of cyclic ketones are made available. Thus, the corresponding 3-alkylated or 3-silylated cycloalkanones and alken-3-ones were prepared via the 1-morpholinoallyllithium compounds.
- Ahlbrecht,Weber
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p. 1018 - 1025
(2007/10/02)
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- Mechanism of the Grignard Adddition Reaction. XVI. Homolytic and Concerted Mechanisms in the Reaction of α,β-Unsatureted Carbonyl Compounds with Grignard Reagents
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Kinetic measurements have shown that the addition of Grignard reagents to α,β-unsaturated carbonyl compounds takes place either by a concerted mechanism or by a homolytic mechanism.Phenylmagnesium bromide, which is incapable of homolysis, reacts rapidly in a 1,4-fashion if an s-cis conformation exists between the C=C and the C=O bonds, but only 1,2-addition takes place if the conformation is s-trans.tert-Butylmagnesium bromide is unsuited to the concerted reaction, but 1,4-addition takes place via homolysis.Primary and secondary Grignard reagents, like phenyl, react rapidly in a concerted manner with s-cis substrates, but unlike phenyl, these Grignard reagents may, with s-trans substrates, produce some 1,4-adduct via the homolytic mechanism.
- Holm, Torkil
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p. 925 - 929
(2007/10/02)
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- Enantioselective Conjugate Addition of Grignard Reagents to Enones Catalyzed by Chiral Zinc(II) Complexes
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Various chiral zinc(II) complexes catalyze the asymmetric 1,4-addition of Grignard reagents to α,β-unsaturated ketones with high chemoselectivities (yields of 1,4-adducts, 83-99 percent), high regioselectivities (1,4/1,2 ratios up to 499) and modest enant
- Jansen, Johan F. G. A.,Feringa, Ben L.
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p. 4168 - 4175
(2007/10/02)
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- Electron Transfer Processes. Part 47. Reactions of Organometallic Reagents Involving Electron Transfer
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Radical chain processes occur in conjugate addition reactions of 2-cycloalkenones with t-BuHgl2(1-), (t-Bu)2CuLi or (t-Bu)3ZnLi as judged by the relative reactivity of 2-cyclopentenone > 2-cyclohexenone and by the effect of CH2=CPh2 as a radical trap.On t
- Russell, Glen A.,Baik, Woonphil,Ngoviwatchai, Preecha,Kim, Byeong Hyo
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p. 170 - 177
(2007/10/02)
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- ORGANOMANGANESE (II) REAGENTS XVI: COPPER-CATALYZED 1,4-ADDITION OF ORGANOMANGANESE CHLORIDES TO CONJUGATED ENONES
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Copper-catalyzed conjugate addition of organomanganese chlorides to conjugated enones in THF, at 0 deg C, leads to the 1,4-addition products in high yields.The scope of the reaction is very large and the results are generally better than those obtained from organomagnesium compounds in the presence of a copper salts as well as from organocopper or cuprate reagents.Furthermore organomanganese chlorides are indisputably cheaper and more stable than the latter.
- Cahiez, Gerard,Alami, Mouad
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p. 3541 - 3544
(2007/10/02)
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- Zinc(II) Catalysed Conjugate Addition of Grignard Reagents to α,β-Unsaturated Ketones
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Zinc(II)-diamine complexes are efficient catalysts for the conjugate additions of Grignard reagents to various α,β-unsaturated ketones.
- Jansen, Johan F. G. A.,Feringa, Ben L.
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p. 741 - 742
(2007/10/02)
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- ULTRASOUND IN ORGANIC SYNTHESIS 16. OPTIMISATION OF THE CONJUGATE ADDITIONS TO α,β-UNSATURATED CARBONYL COMPOUNDS IN AQUEOUS MEDIA.
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Optimisation of the conjugate addition of alkyl groups to α-enones under sonochemical conditions can be effected, especialy by a proper choice of the solvent, most probably because of its stuctural properties.
- Luche, J. L.,Allavena, C.
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p. 5369 - 5372
(2007/10/02)
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- Synthesis and Reactivity toward Acyl Chlorides and Enones of the New Highly Functionalized Copper Reagents RCu(CN)ZnI
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The new and highly functionalized copper reagents RCu(CN)ZnI obtained from readily available primary and secondary alkylzinc iodides by a transmetalation in THF with the soluble salt, CuCN*2LiX, react in good yields with acyl chlorides and enones, respectively, to afford ketones and 1,4-addition products.
- Knochel, Paul,Yeh, Ming Chang P.,Berk, Scott C.,Talbert Jason
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p. 2390 - 2392
(2007/10/02)
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- CONJUGATE ADDITIONS OF GRIGNARD REAGENTS TO α,β-UNSATURATED KETONES MEDIATED BY DIAMINE ZINC(II)MONOALKOXIDES
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A method for zinc mediated 1,4-additions of Grignard reagents with alkoxides as non-tranferable ligands is described.Using a chiral TMEDA analogue upto 14 percent enantiomeric excess was achieved.
- Jansen, Johan F. G. A.,Feringa, Ben L.
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p. 3593 - 3596
(2007/10/02)
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- 1,4-Addition of Triorganozincates and Silyldiorganozincates to α,β-Unsaturated Ketones
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Lithium and magnesium triorganozincates, prepared by combination of ZnCl2(TMEDA) with 3 molar equivalents of RLi or RMgX, or from dialkylzinc and 1 molar equivalent of RLi or RMgX, react with 2-cyclohexen-1-one (1) under mild conditions to produce moderate to good yields of the 1,4-addition products 2.The approximate reactivity order obtained from the product distribution using unsymmetrical zincates is tBuCH2 tBu, Me Me2PhSi.The latter groups are transferred with good selectivity from mixed reagents derived from Me2Zn.This sequence differs strikingly from that exhibited by unsymmetrical cuprates which transfer neopentyl very easily, and also tert-butyl more easily than the corresponding zincates.The methylation with Me3ZnLi is catalyzed by cobalt complexes.Other enones (7-13) generally give poor yields, and the cobalt-catalyzed methylation of isophorone (3) is complicated by a Kharasch-type deconjugation.Mixed silyldialkylzincates, Me2PhSiZnR2Li, produce the β-silyl ketones from a variety of unhindered or moderately hindered enones in practically useful yields; one example of an α,β-unsaturated ester (12) is also included.
- Tueckmantel, Werner,Oshima, Koichiro,Nozaki, Hitosi
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p. 1581 - 1593
(2007/10/02)
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- ORGANOMANGANESE (II) REAGENTS XI. A Study of their Reactions with Cyclic Conjugated Enones : Conjugate Addition and Reductive Dimerization
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The reaction of organomanganese reagents such as RMnX, R2Mn, R3MnLi and R3MnMgX with cyclohexenone has been studied.Two major pathways have been observed : conjugate addition and β reductive dimerization.Similar results have been obtained with organomagnesium compounds in presence of a catalytic amount of manganous salts.
- Cahiez, G.,Alami, M.
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p. 569 - 572
(2007/10/02)
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- Regioselective 1,4-Addition to α,β-Unsaturated Ketones with Grignard Reagents Mediated by (N,N,N',N'-Tetramethylethylenediamine)zinc(II) Chloride
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The reaction of α,β-unsaturated ketones with a THF solution RMgX (3 mol equiv) and ZnCl2*TMEDA (1 mol equiv) followed by NH4Cl gave 1,4-addition products.The products were contaminated by 1,2-addition products when R = Ph and Me but were essentially free of those compounds when R = n-Bu or i-Pr.The yields were highest when X = Cl.Thus the reaction of 2-cyclohexen-1-one with a solution of n-BuMgCl and ZnCl2*TMEDA gave 3-n-butylcyclohexanone (1) in 96percent yield.
- Kjonaas, Richard A.,Vawter, Edward J.
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p. 3993 - 3996
(2007/10/02)
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- CERIUM CHLORIDE-PROMOTED NUCLEOPHILIC ADDITION OF GRIGNARD REAGENTS TO KETONES AN EFFICIENT METHOD FOR THE SYNTHESIS OF TERTIARY ALCOHOLS
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In the presence of anhydrous cerium(III) chloride, Grignard reagents react with ketones to afford addition products in high yields, even though the substrates are susceptible to abnormal reactions with Grignard reagents alone.
- Imamoto, Tsuneo,Takiyama, Nobuyuki,Nakamura, Kamikazu
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p. 4763 - 4766
(2007/10/02)
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- ASYMMETRIC SYNTHESIS USING ENANTIOMERICALLY PURE 2-(p-ANISYLSULFINYL)-2-CYCLOALKENONES
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Conjugate additions of many organometallic reagents to 2-(p-anisylsulfinyl)-2-cycloalkenones, 2, proceed with much greater diastereoselectivity than additions to the corresponding 2-(p-tolylsulfinyl)-2-cycloalkenones, 7.Complexation of 2 with zinc dibromide followed by addition of various Grignard reagents lead, after reductive removal of the sulfoxide, to 3-substituted cycloalkanones of higher optical purity than those obtained from 7.Addition of methyltitanium triisopropoxide to 2-(p-anisylsulfinyl)-2-cyclohexenone, 2b, in the absence of zinc dibromide, proceeds with virtually complete asymmetric induction.
- Posner, Gary H.,Frye, Leah L.,Hulce, Martin
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p. 1401 - 1408
(2007/10/02)
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- ENZYMATIC "IN VITRO" REDUCTION OF KETONES. VI.(1) Reduction rates and stereochemistry of the HLAD-catalyzed reduction of 3-alkyl- and 4-alkylcyclohexanones.
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Reaction rate constants for the catalytic step HLAD-NADH + ketone * HLAD-NAD+ + alcohol in the HLAD-catalyzed reduction of 3-alkyl- and 4-alkylcyclohexanones are determined from initial rate measurements in the coenzyme recycling system ketone-ethanol-NAD+-HLAD.By rate measurements at several temperatures, activation parameters were determined and isokinetic relationships tracked down.Two different isokinetic relationships show that the 3-alkylcyclohexanones pass through an other type of transition state than cyclohexanone and the 4-alkylcyclohexanones, which means that they have a different arrangement on the HLAD-NADH complex.The results are rationalized in view of the most recent principles on nucleophilic additions to carbonyl functions.The resulting model for the HLAD-catalyzed reduction adequately explains the observed rate accelerating and decelerating effects and the stereochemistry of the reduction as well.
- Osselaer, T. A. Van,Lemiere, G. L.,Lepoivre, J. A.,Alderweireldt, F. C.
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p. 133 - 150
(2007/10/02)
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