- Chiral conflict. The effect of temperature on the helical sense of a polymer controlled by the competition between structurally different enantiomers: From dilute solution to the lyotropic liquid crystal state
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Helical polymers appended with paired structurally different enantiomers, which have opposing helical sense preferences, yield a new kind of relationship between optical activity and temperature, and also reveal unusual details of the nature of chiral int
- Tang, Kai,Green, Mark M.,Cheon, Kap Soo,Selinger, Jonathan V.,Garetz, Bruce A.
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Read Online
- Catalytic Regioselective Isomerization of 2,2-Disubstituted Oxetanes to Homoallylic Alcohols
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The selective isomerization of strained heterocyclic compounds is an important tool in organic synthesis. An unprecedented regioselective isomerization of 2,2-disubstituted oxetanes into homoallylic alcohols is described. The use of tris(pentafluorophenyl
- Cabré, Albert,Lledós, Agustí,Rafael, Sergi,Riera, Antoni,Sciortino, Giuseppe,Ujaque, Gregori,Verdaguer, Xavier
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p. 7521 - 7527
(2020/03/24)
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- Asymmetric Umpolung Hydrogenation and Deuteration of Alkenes Catalyzed by Nickel
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Nickel-catalyzed asymmetric hydrogenation of several types of alkenes proceeds in high enantioselectivity, using acetic acid or water as the hydrogen source and indium powder as electron donor. The scope of alkenes herein include α,β-unsaturated esters, n
- Guo, Siyu,Wang, Xiuhua,Zhou, Jianrong Steve
-
supporting information
p. 1204 - 1207
(2020/02/04)
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- CuH-Catalyzed Asymmetric Reduction of α,β-Unsaturated Carboxylic Acids to β-Chiral Aldehydes
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The copper hydride (CuH)-catalyzed enantioselective reduction of α,β-unsaturated carboxylic acids to saturated aldehydes is reported. This protocol provides a new method to access a variety of β-chiral aldehydes in good yields, with high levels of enantioselectivity and broad functional group tolerance. A reaction pathway involving a ketene intermediate is proposed based on preliminary mechanistic studies and density functional theory calculations.
- Zhou, Yujing,Bandar, Jeffrey S.,Liu, Richard Y.,Buchwald, Stephen L.
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p. 606 - 609
(2018/01/26)
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- Enantioselective β-Protonation of Enals via a Shuttling Strategy
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Remote asymmetric protonation is a longstanding challenge due to the small size of protons. Reactions involving electron-deficient olefins pose a further difficulty due to the electrophilic nature of these substrates. We report a shuttling system that delivers a proton in a highly enantioselective manner to the β-carbon of enals using a chiral N-heterocyclic carbene (NHC) catalyst. Choices of a Br?nsted base shuttle and a Br?nsted acid cocatalyst are critical for highly stereoselective β-protonation of the homoenolate intermediate and regeneration of the NHC catalyst results in functionalization of the carbonyl group. Thioesters with a β-chiral center were prepared in a redox-neutral transformation with an excellent yield and ee.
- Chen, Jiean,Yuan, Pengfei,Wang, Leming,Huang, Yong
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p. 7045 - 7051
(2017/06/01)
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- Asymmetric hydrogenation of allylic alcohols using ir?N,P-Complexes
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In this study, a series of γ,γ-disubstituted and β,γ-disubstituted allylic alcohols were prepared and successfully hydrogenated using suitable N,P-based Ir complexes. High yields and excellent enantioselectivities were obtained for most of the substrates studied. This investigation also revealed the effect of the acidity of the N,P?Ir-complexes on the acid-sensitive allylic alcohols. DFT ΔpKa calculations were used to explain the effect of the N,P-ligand on the acidity of the corresponding Ir-complex. The selectivity model of the reaction was used to accurately predict the absolute configuration of the hydrogenated alcohols.
- Li, Jia-Qi,Liu, Jianguo,Krajangsri, Suppachai,Chumnanvej, Napasawan,Singh, Thishana,Andersson, Pher G.
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p. 8342 - 8349
(2018/05/23)
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- Enantioselective Hydrogenation of β,β-Disubstituted Unsaturated Carboxylic Acids under Base-Free Conditions
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An additive-free enantioselective hydrogenation of β,β-disubstituted unsaturated carboxylic acids catalyzed by the Rh-(R,R)-f-spiroPhos complex has been developed. Under mild conditions, a wide scope of β,β-disubstituted unsaturated carboxylic acids were hydrogenated to the corresponding chiral carboxylic acids with excellent enantioselectivities (up to 99.3% ee). This methodology was also successfully applied to the synthesis of the pharmaceutical molecule indatraline.
- Yan, Qiaozhi,Kong, Duanyang,Zhao, Wei,Zi, Guofu,Hou, Guohua
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p. 2070 - 2077
(2016/03/15)
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- CROSS-COUPLING OF UNACTIVATED SECONDARY BORONIC ACIDS
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Provided are methods for site- and stereo-retentive cross-couplings with unactivated secondary boronic acids, particularly useful in building block-based approach for small molecule synthesis. Also provided is a method of forming an air-stable chiral secondary boronic acid.
- -
-
Page/Page column 56; 57
(2015/05/19)
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- Iridium-catalyzed asymmetric hydrogenation of 3,3-disubstituted allylic alcohols in ethereal solvents
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Ir-phosphinomethyl-oxazoline complexes have been identified as efficient, highly enantioselective catalysts for the asymmetric hydrogenation of 3,3-disubstituted allylic alcohols and related homoallylic alcohols. In contrast to other N,P ligand complexes, which require weakly coordinating solvents, such as dichloromethane, these catalysts perform well in more ecofriendly THF or 2-MeTHF. Their synthetic potential was demonstrated with the formal total synthesis of four bisabolane sesquiterpenes. Particularly high enantioselectivity values in the asymmetric hydrogenation of 3,3-disubstituted allylic alcohols and related homoallylic alcohols have been achieved with Ir-phosphinomethyloxazoline catalysts. In contrast to other N,P-ligand complexes, which require weakly coordinating solvents, such as CH 2Cl2, these catalysts perform well in more ecofriendly THF or 2-MeTHF (see scheme; CODa =a 1,5-cyclooctadiene). Copyright
- Bernasconi, Maurizio,Ramella, Vincenzo,Tosatti, Paolo,Pfaltz, Andreas
-
supporting information
p. 2440 - 2444
(2014/03/21)
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- Iridium catalysts with Chiral bicyclic pyridine-phosphane ligands for the asymmetric hydrogenation of olefins
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New bicyclic pyridine-phosphane ligands were prepared, and their iridium complexes were evaluated in asymmetric hydrogenation of trisubstituted olefins with non-coordinating and weakly coordinating substituents. The iridium catalysts showed high reactivity and enantioselectivity for both types of olefins. New pyridine-derived N,P-chelated iridium catalysts were prepared and evaluated in the asymmetric hydrogenation of trisubstituted olefins. High conversions and enantioselectivities were obtained. Copyright
- Quan, Xu,Parihar, Vijay Singh,Bera, Milan,Andersson, Pher G.
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p. 140 - 146
(2014/01/06)
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- Enantioselective isomerization of primary allylic alcohols into chiral aldehydes with the tol-binap/dbapen/ruthenium(II) catalyst
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Efficient isomerization: The title reaction was catalyzed by the [RuCl 2{(S)-tol-binap}{(R)-dbapen}]/KOH system in ethanol at 25°C (see scheme). A series of E- and Z-configured aromatic and aliphatic allylic alcohols, including a simple primary alkyl-substituted compound (E)-3-methyl-2-hepten-1-ol, were transformed into the chiral aldehydes with at least 99 % ee. dbapen=2-dibutylamino-1-phenylethylamine, tol-binap=2,2′- bis(di-4-tolylphosphanyl)-1,1′-binaphthyl. Copyright
- Arai, Noriyoshi,Sato, Keisuke,Azuma, Keita,Ohkuma, Takeshi
-
supporting information
p. 7500 - 7504
(2013/07/26)
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- Ruthenium-catalyzed asymmetric transfer hydrogenation of allylic alcohols by an enantioselective isomerization/transfer hydrogenation mechanism
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Reducing hazards: A asymmetric transfer hydrogen reaction was developed to reduce prochiral allylic alcohols in high yield and excellent enantioselectivity (see example). Mechanistic studies indicate a novel enantioselective isomerization/transfer hydrogenation mechanism. This new reaction is much safer than high-pressure hydrogenation using H2 gas. Copyright
- Wu, Ruoqiu,Beauchamps, Marie G.,Laquidara, Joseph M.,Sowa Jr., John R.
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p. 2106 - 2110
(2012/04/11)
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- Chiral dihydrobenzo[1,4]oxazines as catalysts for the asymmetric transfer-hydrogenation of α,β-unsaturated aldehydes
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A new class of organocatalysts based on the structure of 2,3-dihydrobenzo[1,4]oxazine was prepared and applied in the enantioselective transfer-hydrogenation of α,β-unsaturated aldehydes with Hantzsch ester as hydride donor. These catalysts proved to be particularly effective for the conjugate reduction of β,β-diaryl-substituted acrylaldehydes leading to saturated aldehydes bearing a stereogenic center with two different aryl groups with enantioselectivities of up to 91% ee.
- Ebner, Christian,Pfaltz, Andreas
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supporting information; experimental part
p. 10287 - 10290
(2012/02/01)
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- C-O hydrogenolysis catalyzed by Pd-PMHS nanoparticles in the company of chloroarenes
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Catalytic Pd(OAc)2 and polymethylhydrosiloxane (PMHS), in conjunction with aqueous KF, and a catalytic amount of an aromatic chloride, effects the chemo-, regio-, and stereoselective deoxygenation of benzylic oxygenated substrates at room temperature in THF. Preliminary mechanistic experiments suggest the process to involve palladium-nanoparticle-catalyzed hydrosilylation followed by C-O reduction. The chloroarene additive appears to facilitate the hydrogenolysis process through the slow controlled release of HCl.
- Rahaim, Ronald J.,Maleczka, Robert E.
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p. 584 - 587
(2011/04/23)
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- Proline-based P,O ligand/iridium complexes as highly selective catalysts: Asymmetric hydrogenation of trisubstituted alkenes
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P,O joins the mix: P,O ligands (L1) form efficient iridium catalysts for the asymmetric hydrogenation of olefins. The proline-derived ligands lead to high enantioselectivities with several classes of alkenes, most notably with α,β-unsaturated carboxylic e
- Rageot, Denise,Woodmansee, David H.,Pugin, Benoet,Pfaltz, Andreas
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supporting information; experimental part
p. 9598 - 9601
(2011/12/05)
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- 1,3-Benzodithiole-1,1,3,3-tetraoxide (BDT) as a versatile methylation reagent in catalytic enantioselective Michael addition reaction with enals
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A protocol of an organocatalytic highly enantioselective conjugate addition of nucleophilic BDT to enals has been developed and the versatile Michael adducts serve as useful building blocks for a variety of organic transformations.
- Zhang, Shilei,Li, Jian,Zhao, Sihan,Wang, Wei
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supporting information; experimental part
p. 1766 - 1769
(2010/05/19)
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- Helical triskelion monophosphites as ligands in asymmetric catalysis
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Members of a new family of chiral triskelion P ligands, namely helical C3-symmetric monophos- phites P(OR)3, have been prepared in two steps Dy monoacylation of (R)- or (S)-1,1'-binaphthyl-2,2'-diol (BINOL) or diphenol using a carboxylic acid chloride followed Dy PCl3 phosphorylation. The most sterically hindered member of these monophosphites, derived from the compound accessible by monoacylation of BINOL using adamantane carboxylic acid chloride, has been characterized by X-ray crystallography and NMR spectroscopy as a single well-defined compound. It exists exclusively in the syn conformation, with a propeller-like (twisted) geometry resulting in helicity. Upon utilization of(R)- or (S)-BINOL in the two-step synthesis, the helicity proves to be P or M, respectively. When used as ligands in the Rh-catalyzed asymmetri c hydrogenation of prochiral homoallylic alcohols, these bulky helical ligands lead to respectable enantioselectivities (79-98percent ee). In contrast, the less sterically congested and more flexible BINOL-derived phenyl analogue exists in several conformeric forms, even in the crystal, and this leads to poor enantioselectivity in the model reactions (ee = 32percent). For the purpose of structural comparison, the analogous monophosphites derived from diphenol were also prepared and characterized. These compounds, again in contrast to the BINOL-derived adamantyl derivatives, occur in several different conformeric states.
- Reetz, Manfred T.,Guo, Hongchao,Jun-An, Ma.,Goddard, Richard,Mynott, Richard J.
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supporting information; experimental part
p. 4136 - 4142
(2009/09/05)
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- Asymmetric transfer hydrogenation in aqueous media catalyzed by resin-supported peptide having a polyleucine tether
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A resin-supported N-terminal prolyl peptide having a β-turn motif and a polyleucine tether has been developed for the organocatalytic asymmetric transfer hydrogenation under aqueous conditions. Polyleucine accelerated the reaction in a highly enantioselective manner by providing a hydrophobic microenvironment around the prolyl residue. The investigation of catalyst structures indicates that the l-form of polyleucine is essential for both reaction efficiency and enantioselectivity.
- Akagawa, Kengo,Akabane, Hajime,Sakamoto, Seiji,Kudo, Kazuaki
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scheme or table
p. 461 - 466
(2009/09/06)
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- Catalytic conjugate additions of geminal bis(sulfone)s: Expanding the chemistry of sulfones as simple alkyl anion equivalents
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The value of cyclic gem-bis-(sulfone) 4 as a simple alkyl nucleophile equivalent in catalytic C-C bondforming reactions is demonstrated. The 1,4-type nucleophilic additions of bis-(sulfone) 4 to α,β-unsaturated ketones take place by assistance of catalyti
- Landa, Aitor,Puente, Angel,Santos, J. Ignacio,Vera, Silvia,Oiarbide, Mikel,Palomo, Claudio
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experimental part
p. 11954 - 11962
(2010/05/02)
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- Stereochemical course of baker's yeast mediated reduction of the tri- and tetrasubstituted double bonds of substituted cinnamaldehydes
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A comprehensive study of the stereochemical course of baker's yeast mediated reduction of substituted cinnamaldehydes is reported. Hydride addition to the β position of β-methylcinnamaldehydes preferentially afforded isomers of (3S)-3-phenylbutan-1-ol. The reduction of (E)-2,3-dimethyl- cinnamaldehyde (15) produced a mixture of (2S,3S)- and (2R,3S)-2-methyl-3- phenylbutan-1-ol (13 and 14), respectively, with 93 % ee. Conversely (Z)-2,3-dimethylcinnamal-dehyde (16) afforded, a mixture of 13 and 14 with 33 % ee. Accordingly, the reduction of trisubstituted β-methylcinnam-aldehydes 34 and 35 proceeded with the same stereochemical preference and with higher enantioselectivity to give (S) 3-phenylbutan-1-ol (37). In addition, deuterium, incorporation and 2H NMR studies demonstrated that the addition of the second hydrogen atom to the a position proceeded with very low stereochemical control and the overall process is formally a mixture of cis/trans hydrogen addition to the double bond. Alternatively, α-methylcinnamaldehyde is reduced to (S)-2-methyl-3-phenylpropan-1-ol (24) with preferential addition of the hydride to the opposite β face with good stereochemical control of the irons addition of hydrogen to the double bond. Wiley-VCH Verlag GmbH & Co. KGaA.
- Fronza, Giovanni,Fuganti, Claudio,Serra, Stefano
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experimental part
p. 6160 - 6171
(2010/03/24)
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- Development of new thiazole-based iridium catalysts and their applications in the asymmetric hydrogenation of trisubstituted olefins
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New thiazole-based chiral N,P-ligands that are open-chain analogues of known cyclic thiazole ligands have been synthesized and evaluated in the iridium-catalyzed asymmetric hydrogenation of trisubstituted olefins. Chirality was introduced into the ligands through a highly diastereoselective alkylation using Oppolzer's camphorsultam as chiral auxiliary. In general, the new catalysts are as reactive and selective as their cyclic counterparts for the asymmetric hydrogenation of various trisubstituted olefins. This journal is The Royal Society of Chemistry.
- Cheruku, Pradeep,Paptchikhine, Alexander,Ali, Muhammad,Neudoerfl, Joerg-M.,Andersson, Pher G.
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p. 366 - 373
(2008/10/09)
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- Iridium catalysts with chiral imidazole-phosphine ligands for asymmetric hydrogenation of vinyl fluorides and other olefins
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New chiral bidentate imidazole-phosphine ligands have been prepared and evaluated for the iridium-catalysed asymmetric hydrogenation of olefins. The imidazole-phosphine-ligated iridium catalysts hydrogenated trisubstituted olefins with the same sense of enantiodiscrimination as known iridium catalysts possessing oxazole and thiazole as N-donors. The imidazole-based catalysts were shown to hydrogenate vinyl fluorides, in some cases with the highest ee values published to date.
- Kaukoranta, Paeivi,Engman, Mattias,Hedberg, Christian,Bergquist, Jonas,Andersson, Pher G.
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supporting information; experimental part
p. 1168 - 1176
(2009/05/27)
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- Development of pinene-derived N,P ligands and their utility in catalytic asymmetric hydrogenation
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New diastereomeric N,P-ligands, derived from the natural product (+)-α-pinene, have been synthesized and evaluated in iridium-catalyzed asymmetric hydrogenation. The ligands are tetrahydroquinoline derivatives synthesized directly from commercially available α-pinene utilizing resolution or recrystallization to separate diastereomers. In reduction of a range of different trisubstituted alkenes the catalysts express very different activities ranging from no activity to high activity. One of the catalysts gives good ee values for some substrates. The Royal Society of Chemistry.
- Verendel, J. Johan,Andersson, Pher G.
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p. 5603 - 5610
(2008/09/17)
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- (S,S)-(+)-pseudoephedrine as chiral auxiliary in asymmetric conjugate addition and tandem conjugate addition/α-alkylation reactions
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(Chemical Equation Presented) Organolithium reagents undergo highly regio- and diastereoselective 1,4-addition to (S,S)-(+)-pseudoephedrine enamides furnishing the corresponding β-alkyl-substituted adducts in excellent yields and diastereoselectivities. In addition, the intermediate lithium enolates generated after the conjugate addition step undergo a highly diastereoselective alkylation reaction, furnishing α,β-dialkyl- substituted amides in high yields. The obtained adducts have been converted into chiral nonracemic β-alkyl- and α,β-dialkyl-substituted carboxylic acids and γ-alkyl- and β,γ-dialkyl-substituted alcohols using very simple and high-yielding procedures.
- Reyes, Efraim,Vicario, Jose L.,Carrillo, Luisa,Badia, Dolores,Uria, Uxue,Iza, Ainara
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p. 7763 - 7772
(2007/10/03)
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- Chiral molecular recognition by aluminum tris(2,6-diphenylphenoxide) in an asymmetric 1,4-addition
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A precomplex of a chiral α,β-unsaturated ester and a bulky aluminum oxide is crucial to setting the diastereoselectivity in the 1,4-addition of a Grignard or organolithium reagent. This approach based on chiral recognition broadens the potential of the strategies relying on stoichiometric reagents.
- Ito, Hirotsugu,Nagahara, Takashi,Ishihara, Kazuaki,Saito, Susumu,Yamamoto, Hisashi
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p. 994 - 997
(2007/10/03)
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- Application of P,N-Sulfinyl Imine Ligands to Iridium-Catalyzed Asymmetric Hydrogenation of Olefins
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The utility of a novel class of P,N-ligands incorporating a chiral sulfinyl imine moiety is demonstrated in the iridium-catalyzed hydrogenation of both functionalized and unfunctionalized olefins, in which enantioselectivities of up to 94% are achieved. T
- Schenkel, Laurie B.,Ellman, Jonathan A.
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p. 1800 - 1802
(2007/10/03)
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- SuperQuat N-acyl-5,5-dimethyloxazolidin-2-ones for the asymmetric synthesis of α-alkyl and β-alkyl aldehydes
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The proclivity of α-branched N-2′-benzyl-3′-phenylpropionyl derivatives of (S)-4-benzyl-5,5-dimethyl-, (S)-4-phenyl-5,5-dimethyl-, (S)-4-isopropyl-5,5-dimethyl-, (S)-4-benzyl- and (S)-4-benzyl-5,5-diphenyl-oxazolidin-2-ones to generate directly 2-benzyl-3-phenylpropionaldehyde upon hydride reduction with DIBAL is investigated. The (S)-4-benzyl-5,5-dimethyl-derivative proved optimal for inhibition of endocyclic nucleophilic attack, giving 2-benzyl-3-phenylpropionaldehyde in good yield upon reduction. Application of this methodology for the asymmetric synthesis of chiral aldehydes via diastereoselective enolate alkylation of a range of (S)-N-acyl-4-benzyl-5,5-dimethyloxazolidin-2-ones to afford an array of α-substituted-N-acyl-5,5-dimethyloxazolidin-2-ones (85-94% de) and subsequent reduction with DIBAL afforded directly non-racemic α-substituted aldehydes without loss of stereochemical integrity (87-94% ee). The extension of this protocol for the asymmetric synthesis of β-substituted aldehydes is demonstrated, via the diastereoselective conjugate addition of a range of organocuprates to (S)-N-acyl-4-phenyl-5,5-dimethyloxazolidin-2-ones which proceeds with high diastereoselectivity (generally >95% de). Reduction of the conjugate addition products with DIBAL gives non-racemic β-substituted aldehydes in high yields and in high ee (generally >95% ee). This methodology is exemplified by the asymmetric synthesis of (R)-3-isopropenylhept-6-enal, which has previously been used in the synthesis of (3Z,6R)-3-methyl-6-isopropenyl-3,9-decadien-1-yl acetate, a component of the sex pheromones of the California red scale.
- Bull, Steven D.,Davies, Stephen G.,Nicholson, Rebecca L.,Sanganee, Hitesh J.,Smith, Andrew D.
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p. 2886 - 2899
(2007/10/03)
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- A versatile new catalyst for the enantioselective isomerization of allylic alcohols to aldehydes: Scope and mechanistic studies
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A new planar-chiral bidentate phosphaferrocene ligand (2) has been synthesized and structurally characterized. The derived rhodium complex, [Rh(cod)(2)]BF4, serves as an effective catalyst for asymmetric isomerizations of allylic alcohols to aldehydes, furnishing improved yields, scope, and enantioselectivities relative to previously reported methods. The catalyst is air-stable and can be recovered at the end of the reaction. Mechanistic studies establish that the isomerization proceeds via an intramolecular 1,3-hydrogen migration and that the catalyst differentiates between the enantiotopic C1 hydrogens.
- Tanaka, Ken,Fu, Gregory C.
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p. 8177 - 8186
(2007/10/03)
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- Design, synthesis, and application of a C2 symmetric chiral ligand for enantioselective conjugate addition of organolithium to α,β-unsaturated aldimine
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A C2 symmetric chiral diether ligand, (1R,2R)-1,2-dimethoxy-1,2- diphenylethane, was designed and synthesized on the basis of the concept of an asymmetric oxygen atom. Mediated by the chiral diether, high enantioselectivities were achieved in conjugate addition of organolithiums to naphthaldehyde imine and cyclic and acyclic α,β-unsaturated aldimines. The absolute configuration of the product is predictable by the model.
- Shindo, Mitsuru,Koga, Kenji,Tomioka, Kiyoshi
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p. 9351 - 9357
(2007/10/03)
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- Rhodium(II)-Catalyzed CH Insertions with imino>phenyl-λ3-iodane
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The catalyzed decomposition of imino>phenyl-λ3-iodane (NsN=IPh) resulted in formal insertions into CH bonds, activated by phenyl or vinyl groups, or by O-substituents.Scope and limitations of the reaction were investigated.Yields of up to 84percent were achieved in the most favorable cases.Yields were enhanced by electron-releasing substituents and decreased by steric hindrance.Aziridination competed with allylic insertion with olefinic substrates.The insertion reaction proceeded with retention of configuration.With chiral RhII catalysts, a modest asymmetric induction was observed.A mechanism involving direct insertion by a Rh-complexed nitrene into the CH bond is proposed.
- Naegeli, Ivo,Baud, Corine,Bernardinelli, Gerald,Jacquier, Yvan,Moran, Mary,Mueller, Paul
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p. 1087 - 1105
(2007/10/03)
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- Sterically constrained tricyclic 2-oxazolidinone as excellent chiral auxiliary
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A new class of conformationally rigid 2-oxazolidinones with effectively bulky substituents, derived from the [4+2] cycloadduct of cyclopentadiene and a-oxazolone, serve as extremely powerful chiral auxiliaries for asymmetric alkylations, Diels-Alder reactions and conjugate addition reactions.
- Nakamura, Taiju,Hashimoto, Noriaki,Ishizuka, Tadao,Kunieda, Takehisa
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p. 559 - 562
(2007/10/03)
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- Probing the abilities of synthetically useful serine proteases to discriminate between the configurations of remote stereocenters using chiral aldehyde inhibitors
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The abilities of the synthetically useful serine proteases, subtilisin Carlsberg (SC) and α-chymotrypsin (CT), to discriminate between R- and S-configurations of stereocenters remote from the catalytic site have been explored using chiral aldehyde transition state analog inhibitors as probes. The inhibitors evaluated were (R)- and (S)-3-phenylbutanal and (R)- and (S)-4-phenylpentanal, for which the stereocenters at C-3 and C-4 respectively are distant from the aldehyde functionality that interacts with the catalytic serine residue. The achiral parent compounds, 3-phenylpropanal and 4-phenylbutanal, respectively, were also assessed for reference purposes. Each aldehyde was found to be a competitive inhibitor for both enzymes, with CT being significantly more potently inhibited than SC. Within this series, the presence of an R-center methyl group improved binding significantly over that of the achiral parent aldehyde for both enzymes. In contrast, the effects on binding of S-methyl substituents in the same positions were modest, and generally somewhat deleterious. Furthermore, the greater the separation of the stereocenter from the aldehyde group, the lower the degree of configuration discrimination. The most effective inhibition, and the highest degree of remote stereocenter discrimination, observed was that by CT of (R)-3-phenylbutanal, whose K(I) of 8.4 μM was 61-fold lower than that of its achiral parent 3-phenylpropanal, and 88-fold lower than the K(I) of its S-enantiomer. Molecular mechanics and molecular dynamics calculations were performed to identify each favored aldehyde-enzyme complex and to reveal the binding and orientation differences responsible for the R- and S-enantiomer binding discriminations observed.
- Lee, Taekyu,Jones, J. Bryan
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p. 502 - 508
(2007/10/03)
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- Dispiroketals in Synthesis (Part 14): Functionalised Dispiroketals as New Chiral Auxiliaries; Highly Stereoselective Michael Additions to a Bifunctional, C2-Symmetrical Chiral Auxiliary.
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A bifunctional, C2-symmetrical chiral auxiliary derived from dihydroxylated dispiroketals has been used to induce a high degree of asymmetry in Michael additions of cuprates to a variety of di-α,β-unsaturated ester systems.
- Castle, Grant H.,Ley, Steven V.
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p. 7455 - 7458
(2007/10/02)
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- Stereospecific Friedel-Crafts Alkylation of Aromatic Compounds: Synthesis of Optically Active 2- and 3-Arylalkanoic Esters
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The alkylation of aromatic compounds, such as benzene, toluene, chlorobenzene, and naphthalene, with optically active (S)-alkyl 2-(sulfonyloxy)propionates and (R)-alkyl 3-(sulfonyloxy)butanoates in the presence of AlCl3 afforded optically active (S)-alkyl 2-arylpropionates and (S)-alkyl 3-arylbutanoates in fair to good chemical yields (40-84percent) and in good to excellent optical yields (61-97percent).As usually occurs in Friedel-Crafts alkylation reactions, poor regioselectivity was observed.
- Piccolo, Oreste,Azzena, Ugo,Melloni, Giovanni,Delogu, Giovanna,Valoti, Ermanno
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p. 183 - 187
(2007/10/02)
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- Chiral Homoenolate Equivalents, II. - Asymmetric Synthesis of 3-Substituted 3-Phenylpropionaldehydes via Metallated Chiral Cinnamylamines
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The diastereomeric excess obtained in alkylation reactions of the chiral homoenolate equivalent 22 with prolinol ether as chiral auxiliary leading to the formation of phenylpropionaldehydes 24 depends strongly on the solvent used.The structure of the alkylating reagent on the other hand is not important.The best results (about 9:1) are obtained in tert-butyl methyl ether as solvent.Other chiral auxiliaries testet were uneffective. - Key Words: Chiral homoenolate equivalents / Alkylation / Chiral 1-aminoallyl anions / Chiral aldehydes
- Ahlbrecht, Hubertus,Enders, Dieter,Santowski, Ludger,Zimmermann, Gerd
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p. 1995 - 2004
(2007/10/02)
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- ASYMMETRIC SYNTHESES BASED ON HEXAHYDRO-4,4,7-TRIMETHYL-1,3-BENZOXATHIANS
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Earlier work concerned with a highly stereoselective asymmetric synthesis based on a 1,3-oxathiane as the chiral auxiliary reagent is reviewed and recent applications to the synthesis of the four stereoisomers of malyngolide, of (R)-(+)-γ-caprolactone (a
- Eliel, Ernest L.
-
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- Stereochemistry of Friedel-Crafts Reaction of Benzene with Optically Active 2-Methyloxetane
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The Friedel-Crafts alkylation of benzene with (+)-2-methyloxetane in the presence of Lewis acids (AlCl3, SnCl4, and TiCl4) gave 3-phenyl-1-butanol with 20-60percent inversion of configuration at the reaction center and a mixture of 4-chloro-2-butanol and 3-chloro-1-butanol in optically active form as the by-products. These by-products were formed by the attack of the chlorine atom in Lewis acid. The stereochemical course of the reaction to 3-chloro-1-butanol varied with the kind of catalyst, i.e., inversion with AlCl3 or TiCl4 and retention with SnCl4. The addition of nitromethane to the reaction system promoted the retentive ring-opening to 3-chloro-1-butanol.
- Segi, Masahito,Takebe, Masaki,Masuda, Shinji,Nakajima, Tadashi,Suga, Sohei
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p. 167 - 170
(2007/10/02)
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- Asymmetric Synthesis Catalyzed by Chiral Ferrocenylphosphine-Transition Metal Complexes. 2. Nickel- and Palladium-Catalyzed Asymmetric Grignard Cross-Coupling
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Various kinds of chiral ferrocenylphosphines, which have both planar and central elements of chirality and also a functional group on the side chain, have been used as ligands for nickel or palladium complex catalyzed asymmetric cross-coupling of secondary alkyl (1-phenylethyl, 2-octyl, and 2-butyl) Grignard reagents with organic halides such as vinyl bromide, (E)-β-bromostyrene, 2-bromopropene, and bromobenzene. (S)-N,N-Dimethyl-1-ethylamine was one of the most effective ligands giving the coupling product, 3-phenyl-1-butene, of up to 68percent ee in the reaction of 1-phenylethylmagnesium chloride with vinyl bromide, and it was found that the ferrocene planar chirality is more important than the carbon central chirality and the dimethylamino group is the first requisite for the high selectivity.The stereoselectivity was not affected by introduction of substituents onto the diphenylphosphino group of ligand, but was strongly affected by changing the steric bulkiness of the secondary amino group on the ferrocenylphosphine side chain.A mechanism, where the coordination of the amino group on the ligand with the magnesium atom in the Grignard reagent plays a key role in a diastereomeric transition state, is proposed to account for the ferrocenylphosphine ligands causing a high asymmetric induction.
- Hayashi, Tamio,Konishi, Mitsuo,Fukushima, Motoo,Mise, Takaya,Kagotani, Masahiro,et al.
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p. 180 - 186
(2007/10/02)
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- Synthese chiraler Azobenzole und Untersuchung der in nematischen Fluessigkristallen durch sie induzierten cholesterischen Phasen
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The chiral cis- and trans-azo compounds 8a - d and 9a - d with para- or ortho-standing chiral side chains as well as the trans-azoxy derivatives 17a - d and 18a - d are synthesized.The influence of the molecular structure and the distance of the chiral centre from the aromatic nucleus on screw sense and pitch of induced cholesteric phases is investigated.The cis-azo compounds 9c and d show atropisomerism.
- Heppke, Gerd,Marschall, Helga,Nuernberg, Peter,Oestreicher, Feodor,Scherowsky, Guenter
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p. 2501 - 2518
(2007/10/02)
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- CHIRAL HOMOENOLATE EQUIVALENTS. I. ASYMMETRIC SYNTHESIS OF β-SUBSTITUTED ALDEHIDES VIA METALATED CHIRAL ALLYLAMINES
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Metalated chiral allylamines of type 2 (M = Li, K) are used as chiral homoenolate equivalents and allow after alkylation and acidic hydrolysis asymmetric C-C bond formations to β-substituted aldehydes in enantiomeric excesses up to 67percent.
- Ahlbrecht, Hubertus,Bonnet, Gerhard,Enders, Dieter,Zimmermann, Gerd
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p. 3175 - 3178
(2007/10/02)
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