- Highly enantioselective copper-catalyzed conjugate addition of diethylzinc to nitroalkenes
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Copper-catalyzed asymmetric conjugate addition of diethylzinc to nitroalkenes using new chiral monodentate phosphoramidite ligands proceeds with high enantioselectivity up to 99% ee.
- Choi, Hojae,Hua, Zihao,Ojima, Iwao
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- Enantioselective copper-catalyzed conjugate addition of dialkyl zinc to nitro-olefins
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(equation presented) The copper-catalyzed asymmetric conjugate addition of dialkylzinc onto various nitro-olefins has been carried out with excellent results. An enantiomeric excess of up to 94% was obtained using 0.5% Cu(OTf)2 and 1% of chiral
- Alexakis, Alexandre,Benhaim, Cyril
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- Enantioselective conjugate addition nitro-mannich reactions: Solvent controlled synthesis of acyclic anti - And syn-β-nitroamines with three contiguous stereocenters
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We report an enantioselective conjugate addition nitro-Mannich reaction protocol which combines dialkylzinc, aromatic nitro alkene and imine to form two C-C bonds and three contiguous stereocenters in one reaction vessel. Absolute stereochemistry was controlled from the initial 1,4-addition of dialkylzinc to aromatic nitroalkenes by known copper-chiral ligand catalysts. The choice of solvent dictated the formation of either the syn,anti or syn,syn diastereoisomers, two of the four possible diastereoisomers. The syn,syn isomer is a rare example of a syn-selective nitro-Mannich reaction. The diastereoselectivity is dependent upon the presence or not of Zn(O 2CCF3)2 in the reaction mixture and empirical transition state models are proposed to account for the observed stereochemical course of the two reaction conditions. The extent of enantioselectivity and structural diversity of the process is limited by current methodology for the catalytic asymmetric addition of dialkylzincs to nitrostyrenes. The synthetically versatile products are the most complex β-nitro amines prepared using the nitro-Mannich reaction and are formed in high yield and enantioselectivity.
- Anderson, James C.,Stepney, Gregory J.,Mills, Matthew R.,Horsfall, Lisa R.,Blake, Alexander J.,Lewis, William
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- Chiral NHC ligands bearing a pyridine moiety in copper-catalyzed addition of diethylzinc to nitroalkenes
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Chiral N-heterocyclic carbenes, derived from amino acids containing a pyridine ring, are effective ligands in the enantioselective copper-catalyzed addition of diethylzinc to β-nitroalkenes, which provides access to chiral nitroalkanes. The advantages of this process include high yields, broad and complementary substrate scope, and good to high enantioselectivities.
- Soeta, Takahiro,Hatanaka, Yuichi,Ishizaka, Tomohiro,Ukaji, Yutaka
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- Furanoside phosphite-phosphoroamidite and diphosphoroamidite ligands for Cu-catalyzed asymmetric 1,4-addition reactions
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A sugar-based phosphite-phosphoroamidite and diphosphoroamidite ligand library L1-L5a-g was tested in the asymmetric Cu-catalyzed 1,4-conjugate addition reactions of β-substituted and β,β′-disubstituted enones. Our results indicated that the selectivity was strongly dependent on the ligand parameters and on the substrate structure. Moderate-to-good enantioselectivities (ees up to 84%) were obtained in the 1,4-addition of several types of β-substituted cyclic and linear substrates. Of particular note is the high enantioselectivity (ees up to 90%) obtained for the more challenging β,β′-disubstituted 3-methyl-cyclohexenone.
- Raluy, Eva,Pamies, Oscar,Dieguez, Montserrat,Rosset, Stephane,Alexakis, Alexander
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- Modular asymmetric synthesis of P-chirogenic β-amino phosphine boranes
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(Chemical Equation Presented) A short concise route to β- aminophosphine boranes is presented via the desymmetrization of prochiral phosphine boranes, forming P-chirogenic aldehydes that are rapidly transformed to the target compounds employing reductive
- Johansson, Magnus J.,Andersson, Kristian H. O.,Kann, Nina
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- Asymmetric Synthesis with N-Heterocyclic Carbenes. Application to the Copper-Catalyzed Conjugate Addition
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Chiral N-heterocyclic carbenes are good ligands for the copper-catalyzed conjugate addition of dialkylzinc reagents to various Michael acceptors. With as little as 4% of chiral ligand, the enantioselectivity may reach 93% on cycloheptenone.
- Alexakis, Alexandre,Winn, Caroline L.,Guillen, Frederic,Pytkowicz, Julien,Roland, Sylvain,Mangeney, Pierre
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- Metal-Free Deoxygenation of Chiral Nitroalkanes: An Easy Entry to α-Substituted Enantiomerically Enriched Nitriles
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A metal-free, mild and chemodivergent transformation involving nitroalkanes has been developed. Under optimized reaction conditions, in the presence of trichlorosilane and a tertiary amine, aliphatic nitroalkanes were selectively converted into amines or nitriles. Furthermore, when chiral β-substituted nitro compounds were reacted, the stereochemical integrity of the stereocenter was maintained and α-functionalized nitriles were obtained with no loss of enantiomeric excess. The methodology was successfully applied to the synthesis of chiral β-cyano esters, α-aryl alkylnitriles, and TBS-protected cyanohydrins, including direct precursors of four active pharmaceutical ingredients (ibuprofen, tembamide, aegeline and denopamine).
- Pirola, Margherita,Faverio, Chiara,Orlandi, Manuel,Benaglia, Maurizio
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p. 10247 - 10250
(2021/06/18)
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- Boosting Conjugate Addition to Nitroolefins Using Lithium Tetraorganozincates: Synthetic Strategies and Structural Insights
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We report the first transition metal catalyst- and ligand-free conjugate addition of lithium tetraorganozincates (R4ZnLi2) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R4ZnLi2 provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 °C) and short reaction time (30 min). This is particularly remarkable when employing β-nitroacrylates and β-nitroenones, where despite the presence of other electrophilic groups, selective 1,4 addition to the C=C is preferred. Structural and spectroscopic studies confirmed the formation of tetraorganozincate species in solution, the nature of which has been a long debated issue, and allowed to unveil the key role played by donor additives on the aggregation and structure of these reagents. Thus, while chelating N,N,N’,N’-tetramethylethylenediamine (TMEDA) and (R,R)-N,N,N’,N’-tetramethyl-1,2-diaminocyclohexane (TMCDA) favour the formation of contacted-ion pair zincates, macrocyclic Lewis donor 12-crown-4 triggers an immediate disproportionation process of Et4ZnLi2 into equimolar amounts of solvent-separated Et3ZnLi and EtLi.
- Dell'Aera, Marzia,Perna, Filippo Maria,Vitale, Paola,Altomare, Angela,Palmieri, Alessandro,Maddock, Lewis C. H.,Bole, Leonie J.,Kennedy, Alan R.,Hevia, Eva,Capriati, Vito
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supporting information
p. 8742 - 8748
(2020/07/04)
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- EBINOL axial chiral compound as well as synthesis method and application thereof
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The invention belongs to the field of axial chiral compounds, and discloses an EBINOL axial chiral compound. The EBINOL axial chiral compound has the following general formula(the formula is shown inthe description), wherein R and R are respectively
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Paragraph 0238; 0250-0253
(2019/08/02)
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- CuI-Catalysed Enantioselective Alkyl 1,4-Additions to (E)-Nitroalkenes and Cyclic Enones with Phosphino-Oxazoline Ligands
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Catalytic enantioselective conjugate additions of simple alkyl groups to nitroalkenes or cyclic enones that result in the formation of tertiary C–C bonds are described. For these stereoselective addition reactions, new chiral phosphino-oxazoline ligands w
- Shin, Minkyeong,Gu, Minji,Lim, Sung Soo,Kim, Min-Jae,Lee, JuHyung,Jin, HyeongGyu,Jang, Yun Hee,Jung, Byunghyuck
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p. 3122 - 3130
(2018/07/06)
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- Substrate Scope Evaluation of the Enantioselective Reduction of β-Alkyl-β-arylnitroalkenes by Old Yellow Enzymes 1-3 for Organic Synthesis Applications
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The substrate scope of the old yellow enzyme catalyzed reduction of β-alkyl-β-arylnitroalkenes is investigated. Compounds bearing either alkyl chains of increasing length at the carbon atom in position β to the nitro group or different substituents on the aromatic ring are prepared and submitted to bioreduction, to define the synthetic potential of this enantioselective reaction in the preparation of chiral fine chemicals. The versatility of the resulting nitroalkanes as chiral building blocks is shown by reducing the nitro group into a primary amine and by converting it into a carboxylic acid moiety by Meyer reaction. An "explosion" of chiral products can be observed by combining the highly enantioselective ene-reductase-mediated reduction of nitroalkenes with the chemical versatility of the nitro group.
- Bertolotti, Mattia,Brenna, Elisabetta,Crotti, Michele,Gatti, Francesco G.,Monti, Daniela,Parmeggiani, Fabio,Santangelo, Sara
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p. 577 - 583
(2016/02/23)
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- A novel chiral bisphosphine-thiourea ligand for asymmetric hydrogenation of β,β-disubstituted nitroalkenes
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A novel chiral bisphosphine-thiourea ligand was developed and applied in the highly enantioselective hydrogenation of β,β-disubstituted nitroalkenes (up to 99% yield and 99% ee). With low catalytic loading (0.25 mol %), 98% ee and 98% conversion were obta
- Zhao, Qingyang,Li, Shengkun,Huang, Kexuan,Wang, Rui,Zhang, Xumu
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supporting information
p. 4014 - 4017
(2013/09/02)
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- Deoxycholic acid-derived biaryl phosphites as versatile and enantioselective ligands in the rhodium-catalyzed conjugate addition of arylboronic acids to nitroalkenes
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A highly enantioselective conjugate addition of arylboronic acids to cyclic as well as acyclic aromatic and aliphatic nitroalkenes is presented. The rhodium complexes obtained from deoxycholic acid-derived binaphthyl and flexible biphenyl phosphites showed good activity as well as very high enantioselectivity (ee up to 99%) in the conjugated addition even in the presence of challenging substrates such as 1-nitrocyclohexene or aliphatic acyclic nitroalkenes. Copyright
- Jumde, Varsha R.,Iuliano, Anna
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supporting information
p. 3475 - 3483
(2013/12/04)
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- Nicotinamide-dependent Ene reductases as alternative biocatalysts for the reduction of activated alkenes
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Four NAD(P)H-dependent non-flavin ene reductases have been investigated for their ability to reduce activated C=C bonds in an asymmetric fashion by using 20 structurally diverse substrates. In comparison with flavin-dependent Old Yellow Enzyme homologues, a higher degree of electronic activation was required, because the best activities were obtained with enals and nitroalkenes rather than enones and carboxylic esters. Although FaEO from Fragaria x ananassa (strawberry) and its homologue SlEO from Solanum lycopersicum (tomato) exhibited a narrow substrate spectrum, progesterone 5β-reductase (At5β-StR) from Arabidopsis thaliana (thale cress) and leukotriene B4 12-hydroxydehydrogenase (LTB4DH/PGR) from Rattus norvegicus (rat) appear to be promising candidates, in particular for the asymmetric bioreduction of open-chain enals, nitroalkenes and α,β-unsaturated γ-butyrolactones. Competing nitro reduction and non-enzymatic Weitz-Scheffer epoxidation were largely suppressed. Electronically activated alkenes have been stereoselectively reduced by using a single-enzyme-cofactor system employing nicotinamide-dependent non-flavin ene reductases. Copyright
- Durchschein, Katharina,Wallner, Silvia,MacHeroux, Peter,Schwab, Wilfried,Winkler, Thorsten,Kreis, Wolfgang,Faber, Kurt
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p. 4963 - 4968
(2013/01/14)
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- Highly enantioselective hydrogenation of β,β-disubstituted nitroalkenes
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Building the building blocks: A highly enantioselective hydrogenation of ?-aryl-?-alkyl disubstituted nitroalkenes 1 has been developed. This method results in enantiomerically pure nitroalkanes 2, which are versatile precursors for chemical synthesis.
- Li, Shengkun,Huang, Kexuan,Cao, Bonan,Zhang, Jiwen,Wu, Wenjun,Zhang, Xumu
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supporting information; experimental part
p. 8573 - 8576
(2012/09/10)
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- Readily available hydrogen bond catalysts for the asymmetric transfer hydrogenation of nitroolefins
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This paper focuses on readily accessible thiourea hydrogen bond catalysts derived from amino acids, whose steric and electronic features are modulated by their degree of substitution at the carbinol carbon center. These catalysts were applied in the asymmetric transfer hydrogenation of nitroolefins furnishing the chiral products in up to 99% yield and 86% enantiomeric excess. The proposed catalyst's mode of action is supported by mechanistic investigations.
- Schneider, Jakob F.,Lauber, Markus B.,Muhr, Vanessa,Kratzer, Domenic,Paradies, Jan
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p. 4323 - 4327
(2011/07/08)
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- Reductive biotransformation of nitroalkenes via nitroso-intermediates to oxazetes catalyzed by xenobiotic reductase A (XenA)
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A novel reductive biotransformation pathway for β,β-disubstituted nitroalkenes catalyzed by flavoproteins from the Old Yellow Enzyme (OYE) family was elucidated. It was shown to proceed via enzymatic reduction of the nitro-moiety to furnish the corresponding nitroso-alkene, which underwent spontaneous (non-enzymatic) electrocyclization to form highly strained 1,2-oxazete derivatives. At elevated temperatures the latter lost HCN via a retro-[2 + 2]-cycloaddition to form the corresponding ketones. This pathway was particularly dominant using xenobiotic reductase A, while pentaerythritol tetranitrate-reductase predominantly catalyzed the biodegradation via the Nef-pathway.
- Durchschein, Katharina,Fabian, Walter M. F.,MacHeroux, Peter,Zangger, Klaus,Trimmel, Gregor,Faber, Kurt
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experimental part
p. 3364 - 3369
(2011/06/25)
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- From C2- to D2-symmetry: atropos phosphoramidites with a D2-symmetric backbone as highly efficient ligands in Cu-catalyzed conjugate additions
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Atropos phosphoramidites with the D2-symmetric biphenyl backbone were diastereoselectively prepared with ease from achiral tetrahydroxy biphenyls. This type of ligands is proved to be highly efficient in the Cu-catalyzed conjugate additions of
- Zhang, Hui,Fang, Fang,Xie, Fang,Yu, Han,Yang, Guoqiang,Zhang, Wanbin
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scheme or table
p. 3119 - 3122
(2010/08/07)
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- Copper-catalyzed asymmetric 1,4-conjugate addition of dialkylzinc to enones
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Asymmetric 1,4-conjugation addition of dialkylzinc (diethylzinc and dimethylzinc) to cyclic enones, chalcone and nitroalkenes was achieved by a 25 mol% (R)-6,6'-Br2-BINOL(1f), 25 mol% CuSPh and 100 mol% dicyclohexylmethylamin(Cy2NMe) catalyst system. The Cu(I) catalyst system enables the cyclic enone, chalcone and nitroalkene generality with high enantioselectivity (up to84%ee) and isolated yield (up to 94%) under mild reaction conditions.
- Gou, Shaohua,Ye, Zhongbin,Shi, Leiting,Qing, Dayong,Zhang, Wen,Wang, Yuliang
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experimental part
p. 517 - 522
(2010/10/18)
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- New bis(1-ferrocenylethyl)amine-derived monodentate phosphoramidite ligands for highly enantioselective copper-catalyzed 1,4-conjugate addition
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A new family of chiral bis(1-ferrocenylethyl)amine-derived monodentate phosphoramidite ligands has been prepared and successfully applied in the Cu-catalyzed asymmetric 1,4-conjugate addition of diethylzinc to a variety of α,β-unsaturated compounds, in wh
- Zou, Dong-Yun,Duan, Zheng-Chao,Hu, Xiang-Ping,Zheng, Zhuo
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supporting information; experimental part
p. 235 - 239
(2009/06/06)
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- Sugar-based phosphite and phosphoroamidite ligands for the Cu-catalyzed asymmetric 1,4-addition to enones
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A modular sugar-based phosphoroamidite L1-L5a-g and phosphite L6-L9a-g ligand library was tested in the asymmetric Cu-catalyzed 1,4-conjugate addition reactions of β-substituted (cyclic and linear) and β,β′-disubstituted (cyclic) enones. The selectivity d
- Raluy, Eva,Pamies, Oscar,Dieguez, Montserrat,Rosset, Stephane,Alexakis, Alexander
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experimental part
p. 2167 - 2172
(2010/03/24)
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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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- Catalyst self-adaptation in conjugate addition to nitroalkenes and nitroacrylates: Instant chirality control in diphenylmethane-based phosphoramidite ligands
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The tropos diphenylmethane-based phosphoramidite ligand (A) provides high catalytic activity and enantioselectivity in the Cu catalysis of conjugate addition to nitroalkenes and nitroacrylate, by virtue of instant chirality control in A. Copyright
- Wakabayashi, Kazuki,Aikawa, Kohsuke,Kawauchi, Susumu,Mikami, Koichi
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p. 5012 - 5013
(2008/10/09)
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- Organocatalytic asymmetric transfer hydrogenation of nitroolefins
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We describe a highly efficient and highly enantioselective Hantzsch ester mediated conjugate transfer hydrogenation of β,β-disubstituted nitroolefins that is catalyzed by a Jacobsen-type thiourea catalyst. Copyright
- Martin, Nolwenn J. A.,Ozores, Lidia,List, Benjamin
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p. 8976 - 8977
(2008/02/10)
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- Application of the chiral bis(phosphine) monoxide ligand to catalytic enantioselective addition of dialkylzinc reagents to β-nitroalkenes
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(Chemical Equation Presented) Me-DuPHOS monoxide is shown to be a very effective ligand in the enantioselective copper-catalyzed addition of dialkylzinc reagents to β-nitroalkenes providing access to chiral nitroalkanes. The major advantages of this process are high yields, broad and complementary substrate scope, and high enantioselectivities. The effect of achiral dummy ligands as an additive has also been documented.
- Cote, Alexandre,Lindsay, Vincent N. G.,Charette, Andre B.
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- Influence of the double-bond geometry of the Michael acceptor on copper-catalyzed asymmetric conjugate addition
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Focusing on mechanistic aspects, a study of the influence of the (E)/(Z) double-bond geometry of the Michael acceptor on the enantioselectivity of copper-catalyzed asymmetric conjugate addition reactions has been realized. In spite of numerous articles co
- Vuagnoux-D'Augustin, Magali,Alexakis, Alexandre
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p. 5852 - 5860
(2008/04/13)
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- Chiral amidophosphane-copper-catalyzed asymmetric conjugate addition of dialkylzinc reagents to nitroalkenes
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The copper-amidophosphane-catalyzed asymmetric addition reaction of dialkylzinc reagents with β-aryl and β-alkylnitroalkenes afforded the corresponding nitroalkanes with moderate to good enantioselectivities (54-80% ee). The performance was highly dependent on the reaction procedure where the addition of nitroalkene to the mixture of copper-amidophosphane and dialkylzinc gave higher ee than the addition of dialkylzinc to a mixture of copper-amidophosphane and nitroalkene.
- Valleix, Fanny,Nagai, Kazushige,Soeta, Takahiro,Kuriyama, Masami,Yamada, Ken-Ichi,Tomioka, Kiyoshi
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p. 7420 - 7424
(2007/10/03)
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- Enantioselective copper catalysed 1,4-conjugate addition reactions using chiral N-heterocyclic carbenes
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The preparation of a variety of chiral N-heterocyclic carbene (NHC) precursors is described. The relative merits of imidazolinium salts and silver carbenes as NHC precursors are discussed with respect to their synthesis, stability and performance in the copper catalysed conjugate addition of dialkyl zinc reagents to a variety of Michael acceptors. Enantioselectivities of up to 93% were achieved using as little as 4% of chiral ligand.
- Winn, Caroline L.,Guillen, Frédéric,Pytkowicz, Julien,Roland, Sylvain,Mangeney, Pierre,Alexakis, Alexandre
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p. 5672 - 5695
(2007/10/03)
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- Biphenol-based ligands for Cu-catalyzed asymmetric conjugate addition
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The synthesis and characterization of seven new phosphoramidite ligands are described, as well as their use in copper-catalyzed 1,4-addition of diethylzinc to a wide range of substrates. Enantioselectivities of up to >99.5% are obtained.
- Alexakis, Alexandre,Polet, Damien,Benhaim, Cyril,Rosset, Stephane
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p. 2199 - 2203
(2007/10/03)
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- Efficient Cu-catalyzed asymmetric conjugate additions of alkylzinc reagents to aromatic and aliphatic acyclic nitroalkenes
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An efficient and highly enantioselective (up to 95% ee) Cu-catalyzed method for asymmetric conjugate addition (ACA) of alkylzinc reagents to acyclic disubstituted nitroalkenes is presented. Reactions are typically effected at ambient temperature in the presence of 2 mol % chiral dipeptide phosphine and 1 mol % (CuOTf)2·C6H6. Nitroalkenes bearing aromatic as well as aliphatic substituents readily undergo asymmetric additions.
- Mampreian, Dawn M.,Hoveyda, Amir H.
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p. 2829 - 2832
(2007/10/03)
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- Biphenol-based phosphoramidite ligands for the enantioselective copper-catalyzed conjugate addition of diethylzinc
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Phosphoramidite ligands, based on ortho-substituted biphenols and a chiral amine, induce high enantioselectivities (ee's up to 99%) in the copper-catalyzed conjugate addition of dialkylzinc reagents to a variety of Michael acceptors. Particularly, the best reported ee's were obtained for acyclic nitroolefins.
- Alexakis, Alexandre,Polet, Damien,Rosset, Stephane,March, Sebastien
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p. 5660 - 5667
(2007/10/03)
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- Copper(I) thiolate catalysts in asymmetric conjugate addition reactions
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Equation presented. Full conversion and enantioselectivities up to 83% have been obtained in the conjugate addition reactions of diethyl zinc to Michael acceptors catalyzed by well-defined (chiral) copper(I) aminoarenethiolates. Interesting differences between organozinc or Grignard reagents have been found: for cyclic enones R2Zn reagents afford better results, whereas earlier work showed that RMgX reagents react more selectively with acyclic enones.
- Arink, Anne M.,Braam, Thijs W.,Keeris, Roy,Jastrzebski, Johann T. B. H.,Benhaim, Cyril,Rosset, Stephane,Alexakis, Alexandre,Van Koten, Gerard
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p. 1959 - 1962
(2007/10/03)
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- Stereoselective conjugate addition of diethylzinc to enones and nitroalkenes
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Bidirectionally directed conjugate addition of diethylzinc to enones and nitroalkene was achieved with good enantioselectivity.
- Kang, Jahyo,Lee, Jae Hoon,Lim, Dae Sung
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p. 305 - 315
(2007/10/03)
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- One-pot multi-substrate enantioselective conjugate addition of diethylzinc to nitroalkenes
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A multi-substrate approach is used in the copper-phosphoramidite catalyzed enantioselective conjugate addition of diethylzinc to nitroalkenes, using up to nine different nitroalkenes in a one pot procedure. The 18 products (9 times 2 enantiomers of nine d
- Duursma, Ate,Minnaard, Adriaan J,Feringa, Ben L
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p. 5773 - 5778
(2007/10/03)
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- Dramatic improvement of the enantiomeric excess in the asymmetric conjugate addition reaction using new experimental conditions
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The asymmetric conjugate addition of dialkylzincs is usually performed with Cu(OTf)2 in toluene. We show that by using a copper carboxylate in Et2O, THF, or EtOAc, we strongly improve the enantioselectivity with a given ligand. Ee va
- Alexakis,Benhaim,Rosset,Humam
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p. 5262 - 5263
(2007/10/03)
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- Optimization of new chiral ligands for the copper-catalysed enantioselective conjugate addition of ET2Zn to nitroolefins by high-throughput screening of a parallel library
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A library of chiral ligands 5, obtained with a modular building block strategy from the coupling of sulfonyl chlorides 1a-e, amines 2f-j and aldehydes 4p-t, was screened in the enantioselective, copper-catalysed conjugate addition of Et2Zn to a
- Ongeri, Sandrine,Piarulli, Umberto,Jackson, Richard F. W.,Gennari, Cesare
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p. 803 - 807
(2007/10/03)
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- Novel biphenol phosphoramidite ligands for the enantioselective copper-catalyzed conjugate addition of dialkyl zincs
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Phosphoramidite ligands, based on a chiral amine and atropoisomerically flexible biphenols, induce high enantioselectivities (ee's up to 98%) in the copper-catalyzed conjugate addition of dialkyl zinc reagents to a variety of Michael acceptors.
- Alexakis,Rosset,Allamand,March,Guillen,Benhaim
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p. 1375 - 1378
(2007/10/03)
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- Acceleration of the conjugate addition of diethyl zinc to enones by either Cu(OTf)2 or trivalent phosphorus ligands
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The conjugate addition of diethyl zinc to enones under copper catalysis occurs well with copper (II) trifiate. Other copper salts need a phosphine or phosphite ligand to be efficient. The best combination is copper (II) triflate and triethyl phosphite. A very small amount of copper (II) triflate (0.5%) and triehtyl phosphite (1%) are enough for high yields.
- Alexakis,Vastra,Mangeney
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p. 7745 - 7748
(2007/10/03)
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- Enantioselective Conjugate Addition of Primary Dialkylzinc Reagents to 2-Aryl- and 2-Heteroaryl-nitroolefins Mediated by Titanium-TADDOLates Preparation of Enantioenriched 2-Aryl-alkylamines
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The addition of dialkylzinc to nitroolefins is catalyzed by Lewis acids such as MgBr2, MgI2, and chlorotitanates.Using the (R,R)-Ti-TADDOLates the addition of diethyl-, dibutyl-, and dioctyl zinc to 2-aryl-nitroethenes is shown to be enantioselective with
- Schaefer, Harald,Seebach, Dieter
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p. 2305 - 2324
(2007/10/02)
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- A General Method for the Preparation of 2,2-Disubstituted 1-Nitroalkenes
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A general and expeditious route for the preparation of functionalized 2,2-disubstituted 1-nitroalkenes has been developed.Conjugate 1,4-addition of complex zinc cuprates (RCu(CN)ZnI) to easily obtained (E)-1-nitroalkenes, followed by trapping with phenylselenenyl bromide and subsequent oxidative elimination, afforded the corresponding 2,2-disubstituted 1-nitroalkenes in good yields. 2-Alkyl-2-aryl- and 2,2-dialkyl nitroalkenes 4b-g were prepared in 76-88percent yield and obtained as E/Z isomeric mixtures, slightly favoring the Z isomer (ca. 1.0:1.5, E/Z).
- Denmark, Scott E.,Marcin, Lawrence R.
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p. 3850 - 3856
(2007/10/02)
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- Asymmetric Reduction of Nitro Olefins by Fermenting Bakers' Yeast
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Reduction of a number of 1-nitro-1-alkenes by fermenting bakers' yeast has been found to be enantioselective, resulting in the formation of optically active 1-nitroalkanes.In most cases, optical purities of the products determined by HPLC analysis of MTPA amides were as high as 83-98percent ee.The optimum rate of conversion was obtained when the reaction was carried out at pH 8 and low concentration of substrates.The absolute configuration of resulting (+)-1-nitro-2-phenylpropane was determined to be R by comparing the specific rotation with that of an authentic specimen after reductive hydrolysis to the corresponding aldehyde.
- Ohta, Hiromichi,Kobayashi, Naoki,Ozaki, Kazuhiko
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p. 1802 - 1804
(2007/10/02)
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