- Design of Hemilabile N,N,N-Ligands in Copper-Catalyzed Enantioconvergent Radical Cross-Coupling of Benzyl/Propargyl Halides with Alkenylboronate Esters
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The enantioconvergent radical C(sp3)-C(sp2) cross-coupling of alkyl halides with alkenylboronate esters is an appealing tool in the assembly of synthetically valuable enantioenriched alkenes owing to the ready availability, low toxicity, and air/moisture stability of alkenylboronate esters. Here, we report a copper/chiral N,N,N-ligand catalytic system for the enantioconvergent cross-coupling of benzyl/propargyl halides with alkenylboronate esters (>80 examples) with good functional group tolerance. The key to the success is the rational design of hemilabile N,N,N-ligands by mounting steric hindrance at the ortho position of one coordinating quinoline ring. Thus, the newly designed ligand could not only promote the radical cross-coupling process in the tridentate form but also deliver enantiocontrol over highly reactive alkyl radicals in the bidentate form. Facile follow-up transformations highlight its potential utility in the synthesis of various enantioenriched building blocks as well as in the late-stage functionalization for drug discovery.
- Wang, Peng-Fei,Yu, Jiao,Guo, Kai-Xin,Jiang, Sheng-Peng,Chen, Ji-Jun,Gu, Qiang-Shuai,Liu, Ji-Ren,Hong, Xin,Li, Zhong-Liang,Liu, Xin-Yuan
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p. 6442 - 6452
(2022/04/19)
-
- Asymmetric Aminations and Kinetic Resolution of Acyclic α-Branched Ynones
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An efficient method for asymmetric synthesis of acyclic α-tertiary amine derivatives has been achieved through enantioselective aminations of α-branched ynones with azodicarboxylates enabled by chiral phosphoric acid catalysis. Moreover, kinetic resolution of racemic starting material was realized under these conditions, which gave access to valuable enantioenriched α-substituted ketones. A wide array of α-aryl and alkyl-substitutions, and the substituted alkynyl groups were well compatible with this method, producing both the amination products and the recovered ketones with good to high enantioselectivities.
- He, Faqian,Shen, Guosong,Yang, Xiaoyu
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supporting information
p. 15 - 20
(2021/11/20)
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- Iodoarene-Catalyzed Oxyamination of Unactivated Alkenes to Synthesize 5-Imino-2-Tetrahydrofuranyl Methanamine Derivatives
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Reported here is the room-temperature metal-free iodoarene-catalyzed oxyamination of unactivated alkenes. In this process, the alkenes are difunctionalized by the oxygen atom of the amide group and the nitrogen in an exogenous HNTs2 molecule. This mild and open-air reaction provided an efficient synthesis to N-bistosyl-substituted 5-imino-2-tetrahydrofuranyl methanamine derivatives, which are important motifs in drug development and biological studies. Mechanistic study based on experiments and density functional theory calculations showed that this transformation proceeds via activation of the substrate alkene by an in situ generated cationic iodonium(III) intermediate, which is subsequently attacked by an oxygen atom (instead of nitrogen) of amides to form a five-membered ring intermediate. Finally, this intermediate undergoes an SN2 reaction by NTs2 as the nucleophile to give the oxygen and nitrogen difunctionalized 5-imino-2-tetrahydrofuranyl methanamine product. An asymmetric variant of the present alkene oxyamination using chiral iodoarenes as catalysts also gave promising results for some of the substrates.
- Deng, Xiao-Jun,Liu, Hui-Xia,Zhang, Lu-Wen,Zhang, Guan-Yu,Yu, Zhi-Xiang,He, Wei
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p. 235 - 253
(2021/01/09)
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- Photocatalytic Giese-Type Reaction with Alkylsilicates Bearing C,O-Bidentate Ligands
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Herein, a photocatalytic Giese-type reaction with alkylsilicates bearing C,O-bidentate ligands as stable alkyl radical precursors has been reported. The alkylsilicates were prepared in one step from organometallic reagents. Not only primary, secondary, and tertiary alkyl radicals, but also elusive methyl radicals, could be generated by using the present reaction system. The generated radicals were trapped by electron-deficient olefins bearing various functional groups to give the desired alkyl adducts. The silicon byproduct can be recovered after the photoreaction. The radical generation process was investigated by theoretical calculations, which provided an insight into the facile generation of methyl radicals from methylsilicate bearing C,O-bidentate ligands.
- Morofuji, Tatsuya,Matsui, Yu,Ohno, Misa,Ikarashi, Gun,Kano, Naokazu
-
supporting information
p. 6713 - 6718
(2021/02/26)
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- Harnessing Applied Potential: Selective β-Hydrocarboxylation of Substituted Olefins
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The construction of carboxylic acid compounds in a selective fashion from low value materials such as alkenes remains a long-standing challenge to synthetic chemists. In particular, β-addition to styrenes is underdeveloped. Herein we report a new electrosynthetic approach to the selective hydrocarboxylation of alkenes that overcomes the limitations of current transition metal and photochemical approaches. The reported method allows unprecedented direct access to carboxylic acids derived from β,β-trisubstituted alkenes, in a highly regioselective manner.
- Alkayal, Anas,Buckley, Benjamin R.,Malkov, Andrei V.,Montanaro, Stephanie,Tabas, Volodymyr,Wright, Iain A.
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supporting information
(2020/02/13)
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- Palladium-Catalyzed Alkoxycarbonylation of sec-Benzylic Ethers
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Herein, we report the palladium-catalyzed synthesis of 3-arylpropionate esters starting from secondary benzylic ethers. With this investigation it could be shown that ethers are suitable starting materials in addition to the established carbonylation reactions of olefins, alcohols, or aryl halides.
- Beller, Matthias,Jackstell, Ralf,Maes, Bert U. W.,Schneider, Carolin
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supporting information
(2020/02/25)
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- Palladium catalyzed hydroesterification of substituted alkenes under microwave conditions
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While several catalyst systems have been utilized in the hydroesterification or methoxycarbonylation of alkenes or equivalent substrates, these reactions are conventionally performed in autoclave reactor systems under high CO pressure (20-70 bar) and thermal heating (70 - 110 oC). In this paper, the first methoxycarbonylation reactions performed in a microwave reactor fitted with a gas-Addition accessory system are reported on and compared to the same reactions performed under conventional heating in an autoclave reactor. Thus 1-octene, styrene, allylbenzene, o-and p-methoxyallylbenzene and β-methylstyrene were subjected to methoxycarbonylation over a palladium acetate-aluminum triflate catalyst system at 12 bar and 95 oC. Results obtained indicated the methoxycarbonylation of these alkenes to be much faster under microwave conditions when compared to conventional heating and improvements in conversion ranged between 3 and 5% for the more reactive substrates (1-octene and styrene) and 6 - 20% for the allylbenzenes and β-methylstyrene.
- Du Plessis, Maretha,Marais, Charlene,Bezuidenhoudt, Barend C. B.
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supporting information
p. 40 - 48
(2020/09/16)
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- Photocatalytic Hydromethylation and Hydroalkylation of Olefins Enabled by Titanium Dioxide Mediated Decarboxylation
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A versatile method for the hydromethylation and hydroalkylation of alkenes at room temperature is achieved by using the photooxidative redox capacity of the valence band of anatase titanium dioxide (TiO2). Mechanistic studies support a radical-based mechanism involving the photoexcitation of TiO2 with 390 nm light in the presence of acetic acid and other carboxylic acids to generate methyl and alkyl radicals, respectively, without the need for stoichiometric base. This protocol is accepting of a broad scope of alkene and carboxylic acids, including challenging ones that produce highly reactive primary alkyl radicals and those containing functional groups that are susceptible to nucleophilic substitution such as alkyl halides. This methodology highlights the utility of using heterogeneous semiconductor photocatalysts such as TiO2 for promoting challenging organic syntheses that rely on highly reactive intermediates.
- Zhu, Qilei,Nocera, Daniel G.
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p. 17913 - 17918
(2020/12/04)
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- PYRAZOLOTRIAZOLOPYRIMIDINE DERIVATIVES AS A2A RECEPTOR ANTAGONIST
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Disclosed herein is a pyrazolotriazolopyrimidine derivative or a stereoisomer thereof, or a pharmaceutically acceptable salt thereof useful as an A2A receptor antagonist, and a pharmaceutical composition comprising the same. Also disclosed herein is a method of treating cancer using the pyrazolotriazolopyrimidine derivative or a stereoisomer thereof, or a pharmaceutically acceptable salt thereof as an A2A receptor antagonist.
- -
-
Paragraph 0516; 0518
(2019/11/04)
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- Modeling and optimization of lipase-catalyzed hydrolysis for production of (S)-2-phenylbutyric acid enhanced by hydroxyethyl-β-cyclodextrin
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An efficient reactive system was established to produce (S)-2-phenylbutyric acid (2-PBA) through the enzymatic enantioselective hydrolysis of 2-phenylbutyrate ester (2-PBAE) in aqueous medium. Lipase CALA from Canadian antarctica and hexyl 2-phenylbutyrate (2-PBAHE) were identified upon screening as the best enzyme and substrate, respectively. Adding hydroxyethyl-β-cyclodextrin (HE-β-CD) to improve the solubility of the substrate resulted in a 1.5 times increase in substrate conversion while retaining a high enantioselectivity compared with that when HE-β-CD was not added. The effects of lipase concentration, substrate concentration and HE-β-CD concentration, temperature, pH, and reaction time on enantiomeric excess and conversion rate were investigated, and the optimal conditions were identified using response surface methodology (RSM). Under the optimal conditions, namely 50 mg/mL lipase CALA, 30 mmol/L substrate, 60 mmol/L HE-β-CD, pH of 6.5, temperature of 83 °C and reaction time of 18 h, the enantiomeric excess and overall conversion rate were 96.05% and 27.28%, respectively. This work provides an efficient alternative method for improving the conversion of aromatic ester substrates by including β-cyclodextrin in an aqueous hydrolysis reaction system.
- Zhang, Panliang,Cheng, Qing,Xu, Weifeng,Tang, Kewen
-
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- Enantioselective Copper-Catalyzed Defluoroalkylation Using Arylboronate-Activated Alkyl Grignard Reagents
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A copper-catalyzed system has been introduced for the enantioselective defluoroalkylation of linear 1-(trifluoromethyl)alkenes through C-F activation to synthesize various gem-difluoroalkenes as carbonyl mimics. For the first time, arylboronate-activated alkyl Grignard reagents were uncovered in this cross-coupling reaction. Mechanistic studies confirmed that the tetraorganoborate complexes generated in situ were the key reactive species for this transformation.
- Wang, Minyan,Pu, Xinghui,Zhao, Yunfei,Wang, Panpan,Li, Zexian,Zhu, Chendan,Shi, Zhuangzhi
-
supporting information
p. 9061 - 9065
(2018/08/03)
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- Enantioselective Hydrogen Atom Transfer: Discovery of Catalytic Promiscuity in Flavin-Dependent 'Ene'-Reductases
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Flavin has long been known to function as a single electron reductant in biological settings, but this reactivity has rarely been observed with flavoproteins used in organic synthesis. Here we describe the discovery of an enantioselective radical dehalogenation pathway for α-bromoesters using flavin-dependent 'ene'-reductases. Mechanistic experiments support the role of flavin hydroquinone as a single electron reductant, flavin semiquinone as the hydrogen atom source, and the enzyme as the source of chirality.
- Sandoval, Braddock A.,Meichan, Andrew J.,Hyster, Todd K.
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supporting information
p. 11313 - 11316
(2017/08/30)
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- Indium-Catalyzed Reductive Sulfidation of Esters by Using Thiols: An Approach to the Diverse Synthesis of Sulfides
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A new reductive preparation of unsymmetrical sulfides from esters and thiols in the presence of InI3 and either 1,1,3,3-tetramethyldisiloxane (TMDS) or PhSiH3 as the reductant was developed. This protocol was applied to not only benzoic acid esters that have a methoxy, methyl, chloro, bromo, iodo, or trifluoromethyl group on the aromatic ring but also aliphatic acid esters with either aromatic or aliphatic thiols. A reaction mechanism is proposed by using Hammett plot results and several control experiments. The reductive preparation of unsymmetrical sulfides from esters and thiols by using InI3 and either 1,1,3,3-tetramethyldisiloxane (TMDS) or PhSiH3 was developed. Several mechanistic studies support that the present transformation proceeds through O,S-and S,S-acetals as the reaction intermediates. TMDS = 1,1,3,3-tetramethyldisiloxane, R = aliphatic group.
- Miyazaki, Takahiro,Kasai, Shinsei,Ogiwara, Yohei,Sakai, Norio
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supporting information
p. 1043 - 1049
(2016/03/01)
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- Stereoselective Ketone Rearrangements with Hypervalent Iodine Reagents
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The first stereoselective version of an iodine(III)-mediated rearrangement of arylketones in the presence of orthoesters is described. The reaction products, α-arylated esters, are very useful intermediates in the synthesis of bioactive compounds such as ibuprofen. With chiral lactic acid-based iodine(III) reagents product selectivities of up to 73 % ee have been achieved.
- Malmedy, Florence,Wirth, Thomas
-
supporting information
p. 16072 - 16077
(2016/10/30)
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- Parameters Influencing Reactivity and Regioselectivity in the Methoxycarbonylation of Arylalkenes
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Previous research showed that the steric bulk, electronic character, and bite angle of the ligand have an influence on both the catalyst activity and regioselectivity of hydroformylation and hydroesterification reactions. However, little is known in this regard about the influence of the steric and electronic environment around the double bond of the substrate. A variety of arylalkenes were therefore subjected to methoxycarbonylation to investigate the steric and electronic effects of substituents on the aromatic ring of the substrate on the regioselectivity and reactivity in the methoxycarbonylation reaction of these substrates with a Pd(II)/Al(OTf)3/Ph3P catalyst system.
- Du Plessis, Maretha,Marais, Charlene,Bezuidenhoudt, Barend C. B.
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p. 557 - 565
(2016/02/14)
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- Rh(II)-Catalyzed Reactions of Diazoesters with Organozinc Reagents
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Rh(II)-catalyzed reactions of diazoesters with organozinc reagents are described. Diorganozinc reagents participate in reactions with diazo compounds by two distinct, catalyst-dependent mechanisms. With bulky diisopropylethyl acetate ligands, the reaction mechanism is proposed to involve initial formation of a Rh-carbene and subsequent carbozincation to give a zinc enolate. With Rh2(OAc)4, it is proposed that initial formation of an azine precedes 1,2-addition by an organozinc reagent. This straightforward route to the hydrazone products provides a useful method for preparing chiral quaternary α-aminoesters or pyrazoles via the Paul-Knorr condensation with 1,3-diketones. Crossover and deuterium labeling experiments provide evidence for the mechanisms proposed.
- Panish, Robert,Selvaraj, Ramajeyam,Fox, Joseph M.
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supporting information
p. 3978 - 3981
(2015/09/01)
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- A recyclable CO surrogate in regioselective alkoxycarbonylation of alkenes: Indirect use of carbon dioxide
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Herein, we report a Pd-catalysed alkoxycarbonylation of alkenes based on the use of a recyclable CO2 reduction product, the crystalline and air-stable N-formylsaccharin, as a CO surrogate. The carbonylation proceeds under ambient conditions in an exceptionally complementary regioselective fashion yielding the desired branched products from styrene derivatives and valuable linear esters from alkyl-substituted alkenes.
- Gehrtz,Hirschbeck,Fleischer
-
supporting information
p. 12574 - 12577
(2015/08/06)
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- Cobalt-bisoxazoline-catalyzed asymmetric kumada cross-coupling of racemic α-bromo esters with aryl grignard reagents
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The first cobalt-catalyzed asymmetric Kumada cross-coupling with high enantioselectivity has been developed. The reaction affords a unique strategy for the enantioselective arylation of α-bromo esters catalyzed by a cobalt-bisoxazoline complex. A variety of chiral α-arylalkanoic esters were prepared in excellent enantioselectivity and yield (up to 97% ee and 96% yield). The arylated products were transformed into α-arylcarboxylic acids and primary alcohols without erosion of ee. The new enantioenriched α-arylpropionic esters synthesized herein are potentially useful in the development of nonsteroidal anti-inflammatory drugs. This method was conducted on gram-scale and applied to the synthesis of highly enantioenriched (S)-fenoprofen and (S)-ar-turmerone.
- Mao, Jianyou,Liu, Feipeng,Wang, Min,Wu, Lin,Zheng, Bing,Liu, Shangzhong,Zhong, Jiangchun,Bian, Qinghua,Walsh, Patrick J.
-
supporting information
p. 17662 - 17668
(2015/02/02)
-
- Continuous flow-processing of organometallic reagents using an advanced peristaltic pumping system and the telescoped flow synthesis of (E/Z)-tamoxifen
-
A new enabling technology for the pumping of organometallic reagents such as n-butyllithium, Grignard reagents, and DIBAL-H is reported, which utilises a newly developed, chemically resistant, peristaltic pumping system. Several representative examples of its use in common transformations using these reagents, including metal-halogen exchange, addition, addition-elimination, conjugate addition, and partial reduction, are reported along with examples of telescoping of the anionic reaction products. This platform allows for truly continuous pumping of these highly reactive substances (and examples are demonstrated over periods of several hours) to generate multigram quantities of products. This work culminates in an approach to the telescoped synthesis of (E/Z)-tamoxifen using continuous-flow organometallic reagent-mediated transformations.
- Murray, Philip R. D.,Browne, Duncan L.,Pastre, Julio C.,Butters, Chris,Guthrie, Duncan,Ley, Steven V.
-
supporting information
p. 1192 - 1208
(2013/10/08)
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- Enantioselective hydrogenation of α-substituted acrylic acids catalyzed by iridium complexes with chiral spiro aminophosphine ligands
-
Highly active: Iridium complexes with chiral spiro aminophosphine ligands were synthesized and applied as catalysts for the asymmetric hydrogenation of α-substituted acrylic acids (see scheme). The complexes were highly active catalysts, showing turnover frequencies of up to 6000 h-1, and catalyst loadings could be reduced to 0.01 mol %. Copyright
- Zhu, Shou-Fei,Yu, Yan-Bo,Li, Shen,Wang, Li-Xin,Zhou, Qi-Lin
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supporting information; body text
p. 8872 - 8875
(2012/10/08)
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- Oxidative rearrangement of alkyl aryl/heteroaryl ketones by 1,2-aryl/heteroaryl shift using iodic acid
-
A method for synthesis of α-aryl/heteroaryl alkanoic acids involving oxidative rearrangement of alkyl aryl/heteroaryl ketones by 1,2-aryl/heteroaryl shift using iodic acid is described. ARKAT-USA, Inc.
- Huddar, Sameerana N.,Deshmukh, Swapnil S.,Akamanchi, Krishnacharya G.
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experimental part
p. 67 - 75
(2011/06/19)
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- Kinetic resolution of (R,S)-pyrazolides containing substituents in the leaving pyrazole for increased lipase enantioselectivity
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With hydrolysis of (R,S)-azolides in water-saturated methyl tert-butyl ether (MTBE) via Candida antarctica lipase B (CALB) as the model system, (R,S)-pyrazolides containing a leaving 3-, 4- or 3,4-substituted-pyrazole moiety are selected as the best substrates for preparing various optically pure carboxylic acids containing an α-chiral center. Great improvements of enzyme activity for the (R)-enantiomers with excellent enantioselectivity (VR/VS > 100) are obtainable, if (R,S)-pyrazolides containing a leaving 3- or 3,4-substituted-pyrazole moiety are employed for the hydrolysis or alcoholysis by methanol in anhydrous MTBE. A detailed kinetic analysis for (R,S)-N-2-phenylpropionylpyrazoles indicates that a bulky 3-substituent such as 3-(3-bromophenyl) or 3-(2-pyridyl) in the leaving pyrazole moiety has profound effects on decreasing the nucleophilic attack and proton transfer of catalytic serine for the slow-reacting enantiomer in anhydrous MTBE, as well as that and substrate affinity for both enantiomers in water-saturated MTBE. The resolution platform is also successfully applied to the hydrolysis of (R,S)-pyrazolides in water-saturated cyclohexane via Candida rugosa lipase (Lipase MY) having opposite enantioselectivity to CALB.
- Wang, Pei-Yun,Wu, Chia-Hui,Ciou, Jyun-Fen,Wu, An-Chi,Tsai, Shau-Wei
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experimental part
p. 113 - 119
(2011/02/21)
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- Highly enantioselective hydrogenation of α-aryl-β-substituted acrylic acids catalyzed by Ir-SpinPHOX
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The enantioselective hydrogenation of a series of challenging substrates, α-aryl-β-substituted acrylic acids, was realized with high efficiency and enantioselectivity (up to 96%) under the catalysis of Ir(i) complex of Spiro-based P,N ligand, SpinPHOX.
- Zhang, Yi,Han, Zhaobin,Li, Fuying,Ding, Kuiling,Zhang, Ao
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supporting information; experimental part
p. 156 - 158
(2010/04/02)
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- Synthesis of 3,3-and 4,4-alkyl-phenyl-substituted pyrrolidin-2-one derivatives
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Syntheses of 3,3-and 4,4-alkyl-phenyl-substituted pyrrolidin-2-one derivatives are described. The final compounds were obtained by the reductive cyclization of relevant cyanoalkanoate esters using NaBH4 and CoCl2.6H2O. The obtained pyrroIidin-2-one derivatives are pharmacophoric fragments for the synthesis of various biologically active compounds.
- Kulig,Ignasik,Malawska
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experimental part
p. 1629 - 1636
(2010/07/06)
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- Enantioselective synthesis of β-trifluoromethyl-βlactones via NHC-catalyzed ketene - ketone cycloaddition reactions
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The highly diastereo- and enantioselective synthesis of β-trifluoromethyl-β-lactones bearing two contiguous stereocenters was realized by chiral N-heterocyclic carbene-catalyzed formal cycloaddition reaction of alkyl(aryl)ketenes and trifluoromethyl ketones.
- Wang, Xiao-Na,Shao, Pan-Lin,Lv, Hui,Ye, Song
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supporting information; experimental part
p. 4029 - 4031
(2009/12/06)
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- Asymmetric esterification of ketenes catalyzed by an N-heterocyclic carbene
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The chiral N-heterocyclic carbene precursor 2, derived from L-pyroglutamic acid, was found to be an efficient precatalyst for the enantioselective esterification of alkylarylketenes with benzhydrol to give the corresponding esters in good yields with good to high enantioselectivities (up to 95% ee).
- Wang, Xiao-Na,Lv, Hui,Huang, Xue-Liang,Ye, Song
-
supporting information; experimental part
p. 346 - 350
(2009/03/12)
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- Enantioselective synthesis of dihydrocouniarins via N-heterocyclic carbene-catalyzed cycloaddition of ketenes and o-quinone methides
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Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [4. + 2] cycloaddition reaction of alky(aryl)ketenes and o-quinone methides to give the corresponding 3,3,4-trisubstituted 3,4-dihydrocoumarins in good yields with good dia
- Lv, Hui,You, Lin,Ye, Song
-
body text
p. 2822 - 2826
(2010/03/05)
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- Oxidative rearrangements of arylalkanones with 1H-1-hydroxy-5-methyl-1,2,3-benziodoxathiole 3,3-dioxide, a 'green' analog of Koser's reagent
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Previous methods for the conversion of arylalkanones to alkyl 2-arylesters by oxidative rearrangement utilized reagents which either produced toxic metal salts or halogenated organics as by-products. In this report, 1H-1-hydroxy-5-methyl-1,2,3-benziodoxathiole 3,3-dioxide (HMBI) is used to effect this useful transformation, where the reduced iodine reagent is water-soluble and readily recycled.
- Justik, Michael W.
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p. 3003 - 3007
(2008/02/06)
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- A new synthetic approach to biaryls of the rhazinilam type. Application to synthesis of three novel phenylpyridine-carbamate analogues
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The synthesis of three novel racemic phenylpyridine-carbamate analogues of rhazinilam and their biological evaluation as inhibitors of microtubule assembly and disassembly by interaction with tubulin are described. The sterically hindered ortho-disubstituted biaryl unit as the challenging key structural element is first obtained by a sequential regiocontrolled nucleophilic addition of a lithium ortho-lithiohomobenzylic alkoxide species to 3-bromo-5-oxazolyl pyridine as the electrophile and a subsequent oxidation step. The incorporation of the amino group by replacement of the bromide has been achieved using a Buchwald-Hartwig amination coupling. Ultimate deprotection steps furnished free-amino and free-hydroxyl appendages which were connected by phosgenation to furnish the nine-membered median carbamate ring. This journal is The Royal Society of Chemistry.
- Bonneau, Anne-Laure,Robert, Nicolas,Hoarau, Christophe,Baudoin, Olivier,Marsais, Francis
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p. 175 - 183
(2008/03/28)
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- ANTI-INFECTIVE AGENTS
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Compounds having the formula (I) are hepatitis C (HCV) polymerase inhibitors. Also disclosed are a composition and method for inhibiting hepatitis C (HCV) polymerase, processes for making the compounds, and synthetic intermediates employed in the processes.
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Page/Page column 224
(2010/02/11)
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- Catalytic enantioselective construction of all-carbon quaternary stereocenters: Synthetic and mechanistic studies of the C-acylation of silyl ketene acetals
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With the aid of an appropriate chiral catalyst, acyclic silyl ketene acetals react with anhydrides to furnish 1,3-dicarbonyl compounds that bear all-carbon quaternary stereocenters in good ee and yield. Mechanistic studies provide strong support for a catalytic cycle that involves activation of both the electrophile (anhydride → acylpyridinium) and the nucleophile (silyl ketene acetal → enolate).
- Mermerian, Ara H.,Fu, Gregory C.
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p. 5604 - 5607
(2007/10/03)
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- A facile conversion of aryl alkyl ketones into methyl 2-arylalkanoates using poly[4-(diacetoxyiodo)styrene]
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Treatment of aryl alkyl ketones with poly[4-(diacetoxyiodo)styrene] and trimethyl orthoformate in the presence of sulfuric acid followed by hydrolysis afforded methyl 2-arylalkanoates in good yields. The polymeric reagent can be regenerated and reused as an environmentally benign reagent.
- Sheng, Shou-Ri,Zhong, Ming-Hua,Liu, Xiao-Ling,Luo, Qiu-Yan,Chen, Hui-Zong
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p. 392 - 393
(2007/10/03)
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- Chiral amino ether-controlled catalytic enantioselective arylthiol conjugate additions to α,β-unsaturated esters and ketones: Scope, structural requirements, and mechanistic implications
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Asymmetric conjugate addition reaction of 2-trimethylsilylbenzenethiol with enoates and enones is catalyzed by a chiral amino ether-lithium thiolate complex and affords adducts with high enantioselectivity. Both the s-cis conformation and a steric wall at one side of the carbonyl group are structural requirements in substrates yielding adducts with high enantioselectivity. Reactions with tert-butyl enones gave addition products with high enantioselectivity. Construction of two contiguous chiral centers was possible by this addition-protonation sequence. Methyl tiglate was stereoselectively converted to a single syn-adduct of 95% enantiomeric excess (ee) bearing two contiguous chiral centers. Methyl 2-phenyl-2-butenoate was converted to a single syn-adduct of 95% ee, which was desulfurized to methyl 2-phenylbutanoate of 95% ee. These additions generate a transient lithium enolate that is protonated by a thiol anti to the C-S bond, giving the corresponding product having two adjacent stereocenters.
- Nishimura, Katsumi,Tomioka, Kiyoshi
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p. 431 - 434
(2007/10/03)
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- Observable enols of anhydrides: Claimed literature systems, calculations, and predictions
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The literature describing the observation of enols of carboxylic anhydrides and mixed carboxylic-sulfuric anhydrides was examined. In the phenylbutyric anhydride system, the alleged enol was shown to be ethylphenylketene, and the monoenol EtC(Ph)=C(OH)OC(=O)CH(Ph)Et (5) and the dienol (6) should not be observed according to calculations. Calculations also show that the claimed enols H2C=C(OH)OSO2Y, Y= SO3-, Ac (15) and the enol of 2H-pyran-2,6(3H)-dione (7) are too unstable to be observed. The bulky enols of β,β-ditipylacetic formic (35a) or trifluoroacetic (35b) anhydride were calculated to be unstable with pKEnol=7.7 (6.2). The suggestion that compounds with the 3-acyl or 3-aroyl-2H-pyran-2,6(3H)-dione skeleton are enolic was examined. In the solid state, all the known structures show that enolization takes place on C(5)=O. However, B3LYP/6-31G** calculations show that, for 3-acetyl-4-methyl-2H-pyran-2,6(3H)-dione (10, R1=Me, R2=H), which is completely enolic, the enol on the acetyl group (cf. 12) is only 0.9 kcal/mol more stable than the enol on the anhydride (cf. 11). Calculations also revealed that 3-(trifluoroacetyl)-2H-pyran-2,6(3H)-dione (28) should exist in nearly equal amounts of the enol of anhydride (cf. 30) and the enol of the acyl group (cf. 29), whereas the enol of anhydride (cf. 32) is the only stable species for 3-(methoxycarbonyl)-2H-pyran-2,6(3H)-dione (31). Furan-2,5-diol (27) and 5-hydroxyfuran-2-one (26) are calculated not to give observable isomers of succinic anhydride (25) (pKEnol=30 and 18, resp.) in spite of the expected aromatic stabilization of 27. Surprisingly, the calculations reveal that the enol (NC)2C=C(OH)OCHO (38) is less stable than its tautomeric anhydride (37) (pKEnol=1.6). Comparison of calculated pKEnol values for (NC)2CHC(=O)X (41) and MeC(=O)X indicates that the assumption that substitution by two β-CN groups affects similarly all the systems regardless of X is incorrect. A pKEnol((NC)2CHC(=O)X) vs. pKEnol(MeC(=O)X) plot is linear for most substituents with severe and mild negative deviations, respectively, for X=NH2 and MeO. Appropriate isodesmic reactions have shown that the β,β-(CN)2 substitution increases the stabilization of the enol of amide (X=NH2) by 14.6 kcal/mol over that for the anhydride (X=OCHO), whereas the amide form is 7.1 kcal/mol less destabilized than for the anhydride. The pKEnol value for (MeOCO)2CHCOOCHO (43) is 3.6, i.e., stabilization by these βelectron-withdrawing groups is insufficient to make the enols observable.
- Rappoport, Zvi,Lei, Yi Xiong,Yamataka, Hiroshi
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p. 1405 - 1431
(2007/10/03)
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- Lewis acid-promoted transesterification of N-acyl oxazolidinones under mild conditions
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N-Acyl oxazolidinones are smoothly converted to the corresponding esters by Lewis acid-promoted transesterification. Mild reaction conditions suppress epimerization or racemization of chiral substrates and allow acid-sensitive groups to survive.
- Orita, Akihiro,Nagano, Yoshifumi,Hirano, Junichi,Otera, Junzo
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p. 637 - 639
(2007/10/03)
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- A practical new chiral controller for asymmetric Diels-Alder and alkylation reactions
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(formula presented) The enantiomerically pure hydroxy sulfones (+)- and (-)-2 have been prepared from 1,2-epoxycyclohexane by a simple and practical procedure. The acrylate esters of these alcohols undergo BCl3-catalyzed Diels-Alder reactions with a variety of dienes at -78 to -55°C in CH2Cl2 or C7H8 with high dienophile face selectivity (Table 1). The chiral esters so formed are readily cleaved with recovery of the controllers (+)- or (-)-2. Esters of (+)- and (-)-2 can be converted to Z-polassium enolates and alkylated with high face selectivity.
- Sarakinos, Georgios,Corey
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p. 1741 - 1744
(2008/02/11)
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- Enantiospecific synthesis of 4-(4'-methoxyphenyl)-hexan-3-one as precursor for optically active (pS) or (pR) isomer of (Z) or (E)-3-(2'-((N,N-dimethylamino)methylferrocenyl)-4-(4''-methoxyphenyl)-hex-3-ene
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We describe herein an original method for the preparation of enantiomerically pure (Z)- or (E)-3-(2'-((N,N-dimethylamino)methylferrocenyl)-4-(4''-methoxyphenyl)-hex-3-ene possessing a p(S) or p(R) plane of chirality. The key step of the synthesis lies in obtaining enantiomerically pure (R) or (S) 4-(4'-methoxyphenyl)-hexan-3-one whose reaction with the lithiated N,N-dimethylaminomethylferrocene leads to two enantiomerically pure amino-alcohol diastereomers (pS,3S,4R) and (pR,3S,4R), or (pS,3R,4S) and (pR,3R,4S) respectively. Subsequent dehydration yields a mixture of three olefins, namely, two trisubstituted olefins and either the (Z)- or (E)-tetrasubstituted olefin with respect to the starting amino-alcohol diastereomer. Additionally we obtained the enantiomerically pure (R)- and (S)-4-phenyl-hexan-3-one and the corresponding diastereomeric amino-alcohols.
- Malezieux, Bernard,Gruselle, Michel,Troitskaya, Ludmila,Sokolov, Viatcheslav
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p. 259 - 269
(2007/10/03)
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- Enantioselectivity of the transfer of hydrogen atoms to acyclic prochiral carbon-centred radicals using chiral tin hydrides
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Racemic α-bromo esters 2 have been reduced via prochiral radicals 5 with low to moderate enantioselectivities using chiral tin hydrides 1 with a stereogenic tin atom containing chiral 2-[(1-dimethylaminoalkyl)phenyl] ligands. The tin hydrides 1 were mixtures of diastereomers. It could be shown that the minor diastereomer of tin hydrides 1a and 1b reacts with good enantioselectivity whereas the major diastereomer reacts almost unselectively. The observed enantioselectivities are also strongly influenced by steric effects of the substituents attached to the radical centre.
- Schwarzkopf, Kay,Blumenstein, Michael,Hayen, Ahlke,Metzger, Jürgen O.
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p. 177 - 181
(2007/10/03)
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- Asymmetric construction of benzylic quaternary carbons from chiral malonates: Formal synthesis of both (-)- and (+)-aminoglutethimides AG and analogues
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From a single chiron (R)-(+)-5, available with high enantiomeric excess (97%) by enzymatic hydrolysis (PLE acetonic powder) of a malonate, were prepared convenient precursors of aminoglutethimides (-)-AG-1 and (+)-AG-1. This versatile method also allows preparation of the b-hydroxy ester (R)-9 and its enantiomer (S)-9 as well as the glutethimides (S)-4 and (R)-4 and other analogues.
- Fadel,Garcia-Argote
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p. 1159 - 1166
(2007/10/03)
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- Homolytic Reactions of Ligated Boranes. Part 16. Enantioselective Hydrogen-atom Abstraction by Chiral Amine-Boryl Radicals: Catalytic Kinetic Resolution of Esters and of Camphor
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UV irradiation of an oxirane solution containing di-tert-butyl peroxide, an amine-alkylborane complex (in which the B-alkyl group is optically active) and a racemic ester or camphor as substrate, gives rise initially to the tert-butoxyl radical which rapidly abstracts hydrogen from the complex to form an optically active amine-boryl radical.The amine-boryl radical then abstracts hydrogen enantioselectively from a C-H group α to the carbonyl group in the substrate to regenerate the amine-alkylborane.This abstraction reaction has been used to bring about catalytic kinetic resolution of the substrate, using the bis(isopinocampheylborane) complex of N,N,N',N'-tetramethylethylenediamine and some of its derivatives as catalysts.After partial consumption of the substrate, the amount remaining and its enantiomeric excess (ee) have been used to derive enantioselectivity constants for hydrogen-atom abstraction.Enantioselectivity varies considerably with the structure of the substrate.The highest selectivity was observed for hydrogen abstraction from dimethyl 2,2-dimethyl-1,3-dioxolane-trans-4,5-dicarboxylate, when after 75percent consumption of initially-racemic ester at -90 deg C, the residual substrate showed an ee of 97percent.A transition-state model is proposed to account for the observed enantioselectivities.
- Mok, Pearl L. H.,Roberts, Brian P.,McKetty, Paula T.
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p. 665 - 674
(2007/10/02)
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- ENZYMATIC RESOLUTION OF METHYL 2-ALKYL-2-ARYLACETATES
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Horse liver esterase, used as its inexpensive commercial acetone powder, catalyzes the selective hydrolysis of methy 2-alkyl-2-arylacetates to afford R(-)-2-alkyl-2-arylacetic acids and S(+)-methyl 2-alkyl-2-arylacetates.
- Ahmar, M.,Girard, C.,Bloch, R.
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p. 7053 - 7056
(2007/10/02)
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- W(CO)6 Mediated C-S Bond Cleavage Reactions
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W(CO)6-mediated reactions of thioethers in refluxing chlorobenzene yielded mainly the corresponding dimers.Optically active thioethers give the respective racemic products.Mercaptans, on the other hand, predominantly afford the corresponding reduced products.A deuterium labeling experiments suggest that the SH group is the hydrogen source in the latter reduction reactions.A free-radical mechanism is suggested.
- Ng, Chi Tat,Wang, Xiaojun,Luh, Tien-Yau
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p. 2536 - 2539
(2007/10/02)
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- 3-alkyl-5-(substituted amino)methyl)dihydro-3-phenyl-2(3H)-furanones and imino analogs thereof used for treatment of arrhythmia
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This invention relates to 3-alkyl-5-[(substituted amino) methyl]dihydro-3-phenyl-2(3H)-furanones and imino analogs thereof, and to the pharmaceutical compositions containing such compounds, that are useful as inhibitors of cardiac arrhythmias and are therefore useful in the treatment of irregular heartbeat. This invention also relates to the use of such compounds and pharmaceutical compositions in the treatment of irregular heartbeat.
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- Oxidative Rearrangement of Alkynes to Carboxylic Acid Esters by benzene in Methanol
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A direct synthesis of methyl aryl alkanoate via oxidative rearrangement of alkynes using benzene in methanol is described.
- Moriarty, Robert M.,Vaid, Radhe K.,Duncan, Michael P.,Vaid, Beena K.
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p. 2845 - 2848
(2007/10/02)
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- Conversion of Aromatic Ketones into α-Arylalkanoic Acids. Part 2. Routes Employing Peracid, Chlorine, or Nitrous Acid
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Further methods for effecting the oxidative rearrangement of 1-arylalkanones to α-arylalkanoic esters have been investigated.It has been shown that appropriate α-iodoacetals, readily prepared from the ketones, can be converted into esters on treatment either with a peracid or with chlorine.Using the latter reagent, α-chlorination of the ester can be an unwanted side reaction with some substrates and the factors governing by-product formation are discussed.It is demonstrated that, employing chlorine, the process can be made catalytic in iodine.The acetals of 2-amino-1-arylalkanones have also been shown to give high yields of esters under diazotising conditions adding support to the suggestion that the ion, ArC(OR)2CHR', or an incipient version of the ion, is a key intermediate in the process.
- Higgins, Stanley D.,Thomas, C. Barry
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p. 1483 - 1488
(2007/10/02)
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- 170. Asymmetric Palladium-Assisted Alkylation of Alkenes
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Palladium-promoted alkylation of alkenes using chiral sulfoxide-containing carbanions and chiral lithiated oxazolines results in asymmetric induction (AI) ranging from 3-5 percent (1,5 induction), 20-40 percent (1,3 induction) to 44-52 percent (1,4 induction).No general trend allowing predictions of results was found.With 1-hexene, attack at C(1) is almost exclusive but propene gives a mixture of attack at C(1) and C(2).The use of a chiral ligand together with malonate anion also leads to some asymmetric induction (ca. 20 percent).
- Solladie-Cavallo, Arlette,Haesslein, Jean-Luc
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p. 1760 - 1773
(2007/10/02)
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- Ester Enolates from α-Acetoxy Esters. Synthesis of Aryl Malonic and α-Aryl Alkanoic Esters from Aryl Nucleophiles and α-Keto Esters
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Ester enolates are generated by reductive α-deacetoxylation of α-acetoxy-α-arylmalonic esters or α-acetoxy-α-arylalkanoic esters with lithium in liquid ammonia or sodium α-(dimethylamino)naphthalenide in hexamethylphosphoramide-benzene.Since the requisite α-acetoxy esters are available from aryl nucleophiles, the reductions provide effective new synthetic routes to arylmalonic esters and α-arylalkanoic esters.For example, 2-(p-isobutylphenyl)propionic acid (ibuprofen, a commercially important nonsteroidal antiinflammatory agent) is obtained in 73percent yield overall from isobutylbenzene.Arenes, aryllithiums, or arylmagnesium halides react with α-keto esters, e.g., diethyl oxomalonate, ethyl pyruvate, methyl phenylglyoxalate, or alkyl glyoxylates, to afford α-hydroxy esters.These are acetylated with acetic anhydride-triethylamine and p-(dimethylamino)pyridine as a catalyst.Reductive α-deoxygenation then allows replacement of the acetoxy group by hydrogen or an alkyl group.
- Ghosh, Subrata,Pardo, Simon N.,Salomon, Robert G.
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p. 4692 - 4702
(2007/10/02)
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