- 2,2′-Bipyridine-α,α′-trifluoromethyl-diol ligand: Synthesis and application in the asymmetric Et2Zn alkylation of aldehydes
-
A chiral 2,2′-bipyridine ligand (1) bearing α,α′-trifluoromethyl-alcohols at 6,6′-positions was designed in five steps affording either the R,R or S,S enantiomer with excellent stereoselectivities, i.e. 97% de, >99% ee and >99.5% de, >99.5% ee, respectively. The key step for reaching high levels of stereoselectivity was demonstrated to be the resolution of the α-CF3-alcohol using (S)-ibuprofen as the resolving agent. An initial application for the 2,2′-bipyridine-α,α′-CF3-diol ligand was highlighted in the ZnII-catalyzed asymmetric ethylation reaction of aromatic, heteroaromatic, and aliphatic aldehydes. Synergistic electron deficiency and steric hindrance properties of the newly developed ligand afforded the corresponding alcohols in good to excellent yields (up to 99%) and enantioselectivities (up to 95% ee). As observed from single crystal diffraction analysis, the complexation of the 2,2′-bipyridine-α,α′-CF3-diol ligand generates an unusual hexacoordinated ZnII.
- Lauzon, Samuel,Ollevier, Thierry
-
supporting information
p. 11025 - 11028
(2021/11/03)
-
- A Heck reaction/photochemical alkene isomerization sequence to prepare functionalized quinolines
-
A route to prepare functionalized quinolines based on a Heck reaction/UV-induced alkene isomerization sequence is described. The method allows for the preparation of quinolines under mild and neutral conditions and has broad functional group tolerance. Acid-sensitive functional groups that would not be tolerated under previous approaches can be included and a one-pot quinoline forming procedure is also reported.
- Donohoe, Timothy J.,Hoff, Oskar,Hoffman, Jack B.,Kelly, Alex,Walker, Johannes C. L.,Werrel, Simon
-
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- Asymmetric transfer hydrogenation of cycloalkyl vinyl ketones to allylic alcohols catalyzed by ruthenium amido complexes
-
A chemoselective 1,2-reduction of cycloalkyl vinyl ketones via asymmetric transfer hydrogenation is described. The reduction proceeded smoothly with a chiral diamine ruthenium complex as a catalyst and a HCOOH-NEt3 azeotrope as both a hydrogen source and solvent under mild conditions. A wide range of 1-cycloalkyl chiral allylic alcohols were obtained in good yields and up to 87% ee. It was found that the alkyl group plays an important role in the enantioselectivity.
- Liu, Sensheng,Cui, Peng,Wang, Juan,Zhou, Haifeng,Liu, Qixing,Lv, Jinliang
-
supporting information
p. 264 - 267
(2019/01/10)
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- Br?nsted Acid Enabled Nickel-Catalyzed Hydroalkenylation of Aldehydes with Styrene and its Derivatives
-
A Br?nsted acid enabled nickel-catalyzed hydroalkenylation of aldehydes and styrene derivatives has been developed. The Br?nsted acid acts as a proton shuttle to transfer a proton from the alkene to the aldehyde, thereby leading to an economical and byproduct-free coupling. A series of synthetically useful allylic alcohols were obtained through one-step reactions from readily available styrene derivatives and aliphatic aldehydes in up to 88 % yield and with high linear selectivity.
- Han, Xing-Wang,Zhang, Tao,Zheng, Yan-Long,Yao, Wei-Wei,Li, Jiang-Fei,Pu, You-Ge,Ye, Mengchun,Zhou, Qi-Lin
-
supporting information
p. 5068 - 5071
(2018/03/27)
-
- Synthesis of Chiral α,β-Unsaturated γ-Amino Esters via Pd-Catalyzed Asymmetric Allylic Amination
-
A Pd-catalyzed asymmetric allylic amination of 4-substituted 2-acetoxybut-3-enoates with amines has been developed for the regiospecific synthesis of chiral α,β-unsaturated γ-amino esters. The desired chiral aminated products can be obtained in up to 98%
- Xia, Chao,Shen, Jiefeng,Liu, Delong,Zhang, Wanbin
-
supporting information
p. 4251 - 4254
(2017/08/23)
-
- Copper-Catalyzed Enantioselective Conjugate Addition to α,β-Unsaturated Aldehydes with Various Organometallic Reagents
-
β-Substituted aldehydes constitute a very important class of compounds found in nature. Synthesis of this motif can be envisioned by C-C bond formation on enals. For this purpose, we report herein the development of enantioselective copper-catalyzed conjugate addition of various organometallic reagents to α,β-unsaturated aldehydes with (R)-H8BINAP, (R)-TolBINAP, and (R)-SEGPHOS as chiral ligands. Three sets of conditions were successfully developed and several enals were used. Reactivity and regio- and enantioselectivities were strongly dependent on reaction conditions and substrates. Good to excellent regio- and enantioselectivities were obtained with zinc reagents R2Zn and aluminum reagents R3Al. However, the asymmetric conjugate addition of Grignard reagents afforded only moderate to good regio- and enantioselectivities.
- Goncalves-Contal, Sylvie,Gremaud, Ludovic,Palais, La?titia,Babel, Lucille,Alexakis, Alexandre
-
p. 3301 - 3308
(2016/09/12)
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- Electrophilic Cyanation of Boron Enolates: Efficient Access to Various β-Ketonitrile Derivatives
-
The highly efficient electrophilic cyanation of boron enolates using readily available cyanating reagents, N-cyano-N-phenyl-p-toluenesulfonamide (NCTS) and p-toluenesulfonyl cyanide (TsCN), is reported. Various β-ketonitriles were prepared by this new protocol, which has a remarkably broad substrate scope compared to existing methods. The present method also allowed efficient synthesis of β-ketonitriles containing a quaternary α-carbon center. In addition, a preliminary result with the use of a chiral boron enolate for the enantioselective cyanation reaction is described.
- Kiyokawa, Kensuke,Nagata, Takaya,Minakata, Satoshi
-
p. 10458 - 10462
(2016/08/24)
-
- Nazarov cyclization of divinyl ketones bearing an ester group at the β-position: A remarkable effect of α-substitution and alkene geometry on regioselectivity
-
The Nazarov cyclization of divinyl ketones with an ester at the β-position was examined with particular reference to where the cyclic double bond forms. We observed unprecedented regioselectivity, dictated by the subtle substitution patterns at the α-position and alkene geometry of α,β and mostly, this selectivity is regardless of substitutions at α′- and β′-positions. The major implications of these observations are an aromatic group at the α-position with E-olefin geometry provides a cyclopentenone in which the double bond is not in conjugation with an ester, whereas Z-olefin provides a cyclopentenone in which the double bond is in conjugation with an ester; and divinyl ketones bearing an ester group at the β-position and an alkyl group at the α-position with E-olefin geometry provide a cyclopentenone in which the double bond is in conjugation with the ester.
- Sudhakar, Gangarajula,Raghavaiah, Jakka,Mahesh, Gaddam,Singarapu, Kiran Kumar
-
supporting information
p. 2866 - 2872
(2016/03/12)
-
- Pincer-Nickel-Catalyzed Allyl-Aryl Coupling between Allyl Methyl Ethers and Arylzinc Chlorides
-
The P,N,N-pincer nickel complex [Ni(Cl){N(2-Ph2PC6H4)(2′-Me2NC6H4)}]-catalyzed allyl-aryl coupling was studied. The reaction of allyl methyl ethers, including (1-methoxyallyl)arenes and (3-methoxyprop-1-en-1-yl)arenes, with arylzinc chlorides afforded linear (E)-alkenes in high yields, whereas the reaction of (E)-1-methoxytridec-2-ene with p-Me2NC6H4ZnCl generated a mixture of linear and branched alkenes.
- Tao, Jian-Long,Yang, Bo,Wang, Zhong-Xia
-
p. 12627 - 12634
(2016/01/09)
-
- Synthetic, structural, NMR and catalytic studies of phosphinic amide-phosphoryl chalcogenides (chalcogen = O, S, Se) as mixed-donor bidentate ligands in zinc chemistry
-
ortho Substituted (diphenylphosphoryl)-, (diphenylphosphorothioyl)- and (diphenylphosphoroselenoyl)-phosphinic amides o-C6H 4(P(X)Ph2)(P(O)NiPr2) (X = O (20a), S (20b), Se (20c)) were synthesized by ortho directed lithiation of N,N-diisopropyl-P,P-diphenylphosphinic amide (Ph2P(O)N iPr2) followed by trapping with Ph2PCl and subsequent oxidation of the o-(diphenylphosphine)phosphinic amide (19) with H2O2, S8 and Se. The reaction of the new mixed-donor bidentate ligands with zinc dichloride afforded the corresponding complexes [ZnCl2(P(X)Ph2)o-C6H 4(P(O)NiPr2)] (21a-c). The new compounds were structurally characterized in solution by nuclear magnetic resonance spectroscopy and in the solid-state by X-ray diffraction analysis of the ligand (20b) and the three complexes (21a-c). The X-ray crystal structure of 20b suggests the existence of a PO→P(S)-C intramolecular nonbonded interaction. The natural bond orbital (NBO) analysis using DFT methods showed that the stabilization effect provided by a nO→σ* P-C orbital interaction was negligible. The molecular structure of the complexes consisted of seven-membered chelates formed by O,X-coordination of the ligands to the zinc cation. The metal is four-coordinated by binding to the two chlorine atoms showing a distorted tetrahedral geometry. Applications in catalysis revealed that hemilabile ligands 20a-c act as significant promoters of the addition of diethylzinc to aldehydes, with 20a showing the highest activity. Chelation of Et2Zn with 20a was evidenced by NMR spectroscopy.
- Del Aguila-Sanchez, Miguel A.,Santos-Bastos, Neidemar M.,Ramalho-Freitas, Maria C.,Garcia Lopez, Jesus,Costa De Souza, Marcos,Camargos-Resende, Jackson A. L.,Casimiro, Maria,Alves-Romeiro, Gilberto,Iglesias, Maria Jose,Lopez Ortiz, Fernando
-
p. 14079 - 14091
(2014/11/12)
-
- Synthesis and structure-activity relationship study of substituted caffeate esters as antinociceptive agents modulating the TREK-1 channel
-
The TWIK-related K+ channel, TREK-1, has recently emerged as an attractive therapeutic target for the development of a novel class of analgesic drugs. It has been reported that TREK-1 -/- mice were more sensitive than wild-type mice to painful stimuli, suggesting that activation of TREK-1 could result in pain inhibition. Here we report the synthesis of a series of substituted caffeate esters (12a-u) based on the hit compound CDC 2 (cinnamyl 3,4-dihydroxyl-α-cyanocinnamate). These analogs were evaluated for their ability to modulate TREK-1 channel by electrophysiology and for their in vivo antinociceptive activity (acetic acid induced-writhing assay) leading to the identification a series of novel molecules able to activate TREK-1 and displaying potent analgesic activity in vivo.
- Rodrigues, Nuno,Bennis, Khalil,Vivier, Delphine,Pereira, Vanessa,Chatelain, Franck C.,Chapuy, Eric,Deokar, Hemantkumar,Busserolles, Jér?me,Lesage, Florian,Eschalier, Alain,Ducki, Sylvie
-
supporting information
p. 391 - 402
(2014/03/21)
-
- C-X (X=Br, I) bond-tolerant aerobic oxidative cross-coupling: A strategy to selectively construct β-aryl ketones and aldehydes
-
Using moelcular oxygen as the terminal oxidant, various aryl halide-containing β-aryl ketones and aldehydes can be synthesized directly from readily available allyic alcohols and boronic acids via palladium-catalyzed oxidative cross-coupling reactions. The dual roles of copper, including electron-carrier and Lewis acid functions, are supposed to be critical for the high reactivity and selectivity of this aerobic oxidative coupling transformation. Copyright
- Chen, Mao,Wang, Jie,Chai, Ziyi,You, Cai,Lei, Aiwen
-
supporting information; scheme or table
p. 341 - 346
(2012/05/04)
-
- Catalytic enantioselective β-alkylation of α,β-unsaturated aldehydes by combination of transition-metal- and aminocatalysis: Total synthesis of bisabolane sesquiterpenes
-
Branching out! The first co-catalytic enantioselective (up to 98:2 e.r.) β-alkylation of α,β-unsaturated aldehydes by combination of simple chiral amine and copper catalysts provides β-branched aldehydes in a one-pot protocol (see scheme). The methodology was applied to the short total syntheses of bisabolane sesquiterpenes (S)-(+)-curcumene, (E)-(S)-(+)-3- dehydrocurcumene and (S)-(+)-tumerone.
- Afewerki, Samson,Breistein, Palle,Pirttil?, Kristian,Deiana, Luca,Dziedzic, Pawel,Ibrahem, Ismail,C?rdova, Armando
-
supporting information; experimental part
p. 8784 - 8788
(2011/09/15)
-
- Phosphonium salt catalyzed addition of diethylzinc to aldehydes
-
The addition of diethylzinc to aromatic, heteroaromatic, and aliphatic aldehydes at room temperature is efficiently catalyzed by 1-7 mol% tetrabutylphosphonium chloride. The corresponding addition products are obtained in good to excellent yields of up to 99%. Moreover, polymer bond phosphonium salts can be used to catalyze this reaction with excellent recovery of the polymer bond catalyst up to three cycles. The application of chiral bifunctional phosphonium salts revealed a remarkable counter anion effect. Changing the anion, the activity of the tetrabutylphosphonium salt decreased in the order Cl- > Br- > I- ≈ TsO- > BF4- ≈ PF6-. However, the nature of the cation had also significant influence. Tetraalkyl-ammonium chlorides showed similar activity compared to phosphonium chlorides, while alkaline metal chlorides proved to be considerably less active. Georg Thieme Verlag Stuttgart.
- Werner, Thomas,Riahi, Abdol Majid,Schramm, Heiko
-
experimental part
p. 3482 - 3490
(2011/12/04)
-
- Structure-based optimization of click-based histone deacetylase inhibitors
-
Previously, we reported a click-chemistry based approach to the synthesis of a novel class of histone deacetylase (HDAC) inhibitors [1]. The lead compound NSC746457 was found to be as potent as SAHA (Vorinostat). Further optimization of NSC746457 by using
- Hou, Jingli,Feng, Congran,Li, Zhonghua,Fang, Qinghong,Wang, Huihui,Gu, Guoxian,Shi, Yikang,Liu, Pi,Xu, Feng,Yin, Zheng,Shen, Jie,Wang, Peng
-
supporting information; experimental part
p. 3190 - 3200
(2011/07/29)
-
- Copper-catalyzed enantioselective 1,4-addition to α,β- unsaturated aldehydes
-
Figure presented The first asymmetric Cu-catalyzed conjugate addition of dialkylzinc zinc reagents to a large scope of enals in presence of phosphoramidite, SimplePhos, or (R)-BINAP ligands with enantiomeric excesses up to 90% is reported. Moreover, ACA of Grignard reagents afforded moderate to good 1,4-regioselectivities with enantioselectivities up to 90%.
- Palais, Laetitia,Babel, Lucille,Quintard, Adrien,Belot, Sebastien,Alexakis, Alexandre
-
supporting information; experimental part
p. 1988 - 1991
(2010/07/10)
-
- Chemoselective conjugate reduction of α,β-unsaturated ketones catalyzed by rhodium amido complexes in aqueous media
-
Although a notable feature of Noyori's Ru-TsDPEN complex is that the transfer hydrogenation reaction is highly chemoselective for the C-O functional group and tolerant of alkenes, our early report indicated that the chemoselectivity could be switched from C-O to C-C bonds in the transfer hydrogenation of activated α,β-unsaturated ketones. Now we have found that a variety of α,β-unsaturated ketones, even without other electron-withdrawing functional groups, could be reduced on the alkenic double bonds with high selectivities employing amido-rhodium hydride complex in aqueous media, and up to 100% chemoselectivity has been achieved. It is notable that the chemoselectivity was improved significantly on going from organic solvent to water. Moreover, a 1,4-addition mechanism has been proposed on the basis of the corresponding experimental details and computational analysis.
- Li, Xuefeng,Li, Liangchun,Tang, Yuanfu,Zhong, Ling,Cun, Linfeng,Zhu, Jin,Liao, Jian,Deng, Jingen
-
supporting information; experimental part
p. 2981 - 2988
(2010/07/05)
-
- Free-radical-initiated coupling reaction of alcohols and alkynes: Not co but C-C bond formation
-
This work demonstrates an efficient method to prepare allylic alcohols via direct C-C bond formation using electron-rich alkynes and aliphatic alcohols initiated by tert-butyl hydroperoxide.
- Liu, Zhong-Quan,Sun, Liang,Wang, Jian-Guo,Han, Jie,Zhao, Yan-Kai,Zhou, Bo
-
supporting information; scheme or table
p. 1437 - 1439
(2009/09/07)
-
- Co-metal-free enantioselective conjugate addition reactions of zinc reagents
-
Asymmetric conjugate addition of diethylzinc to cinnamaldehyde in a co-metal-free fashion by using N,O-ligands with planar and central chirality is described. Different modulations of the ligand structure, including several combinations of the chiral units, indicate that a [2.2]paracyclophane backbone is essential for the activity and the enantioselectivity of the generated active catalyst. By using the optimized ligand, an isolated yield of 90 % was obtained with up to 99 % ee.
- Ay, Sefer,Nieger, Martin,Braese, Stefan
-
experimental part
p. 11539 - 11556
(2009/12/07)
-
- Convenient synthesis of a new class of chiral hydroxymethyl-dihydrooxazole ligands and their application in asymmetric addition of diethylzinc to aromatic aldehydes
-
A number of chiral hydroxymethyl-substituted dihydrooxazoles were synthesized from D- or L-mandelic acid and amino alcohols. The chiral ligands thus obtained were tested as catalyst in the asymmetric addition of diethylzinc to aromatic aldehydes, and the
- Li, Zhi-Ting,Li, Xin-Sheng,Li, Liang-Chao,Xu, Dong-Cheng
-
p. 545 - 549
(2007/10/03)
-
- The synthesis of N,O-ferrocenyl pyrrolidine-containing ligands and their application in the diethyl- and diphenylzinc addition to aromatic aldehydes
-
(Chemical Equation Presented) A facile route to a series of planar chiral N,O-ferrocenyl pyrrolidine-containing ligands with varying substituents at the nitrogen and oxygen donor atoms is described. The oxygen donor atom was introduced via a diastereoselective ortho-metalation of N-methylpyrrolidinyl and N-allylpyrrolidinyl ferrocene intermediates and was quenched with various ketones. The nitrogen substituent was varied through deallylation and subsequent derivatization of a secondary pyrrolidine. The efficacy of these novel ligands was investigated in the enantioselective addition of diethylzinc and diphenylzinc to aromatic aldehydes. The ligands proved highly effective in the diethylzinc addition to benzaldehyde that resulted in high yields of up to 99% and enantioselectivities (ee's) of up to 95%. The role of planar chirality was explored and the results indicated that the planar chirality, and not the central chirality, of the ferrocenyl ligands was the dominant stereo-controlling element. Employment of a mixed ethyl-phenylzinc reagent in the phenylation of aromatic aldehydes led to a mixture of the two additional products, and the phenylated product was obtained in up to 37% ee.
- Ahern, Theresa,Mueller-Bunz, Helge,Guiry, Patrick J.
-
p. 7596 - 7602
(2007/10/03)
-
- The epoxy-Ramberg-Baecklund reaction (ERBR): A sulfone-based method for the synthesis of allylic alcohols
-
The epoxy-Ramberg-Baecklund reaction (ERBR) is outlined, in which α,β-epoxy sulfones are converted into a range of mono-, di- and tri-substituted allylic alcohols, on treatment with base. Modification of this method enabled the preparation of enantio-enriched allylic alcohols following the diastereoselective epoxidation of enantio-enriched vinyl sulfones that were accessed efficiently from the chiral pool. The scope, optimisation and limitations of the ERBR as a method for the preparation of allylic alcohols are discussed. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Evans, Paul,Johnson, Paul,Taylor, Richard J. K.
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p. 1740 - 1754
(2007/10/03)
-
- O-DPPB-directed copper-mediated and -Catalyzed allylic substitution with grignard reagents
-
The ortho-diphenylphosphanylbenzoyl (o-DPPB) group was explored as a directing leaving group in copper-mediated and copper-catalyzed allylic substitution with Grignard reagents. Complete control of chemo-, regio- and stereoselectivity with complete syn-1,3-chirality transfer was observed as a result of the directed nature of the reaction. No excess of or ganometallic reagent is required and the directing group can be recovered quantitatively. Coordination studies in the solid state and in solution have shown that two substrates are bound via the phosphine function of the directing group at copper. Dynamic NMR experiments in solution are in agreement with a ligand-exchange process at copper, a prerequisite for the development of a substoichiometric process.
- Demel, Peter,Keller, Manfred,Breit, Bernhard
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p. 6669 - 6683
(2008/09/16)
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- Development of an anomalous heck reaction: Skeletal rearrangement of divinyl and enyne carbinols
-
(Chemical Equation Presented) A general set of conditions that achieves the union of aryl halides and divinyl or enyne carbinols to afford tri- or tetrasubstituted olefins in good yields (up to 83%) is described. The mechanism by which this proceeds is believed to involve the intermediacy of a cyclopropanol, followed by a novel skeletal reorganization. The ability to suppress β-hydride elimination of organopalladium intermediates appears to be critical to the success of these processes.
- Ndungu, J. Maina,Larson, Kimberly K.,Sarpong, Richmond
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p. 5845 - 5848
(2007/10/03)
-
- Formation and reactions of alkylzinc reagents in room-temperature ionic liquids
-
The presence of a suitable amount of bromide or chloride ions was found to be critical in forming the alkylzinc reagents from alkyl iodides and zinc metal in the room-temperature ionic liquid, N-butylpyridinium tetrafluoroborate. β-Hydride transfer in the reactions of butylzinc reagents with aldehydes can also be reduced by a bromide ion.
- Law, Man Chun,Wong, Kwok-Yin,Chan, Tak Hang
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p. 10434 - 10439
(2007/10/03)
-
- Pd-catalyzed nucleophilic allylic alkylation of aliphatic aldehydes by the use of allyl alcohols
-
Under catalysis of Pd(OAc)2-(P-n-Bu)3, Et 2Zn promotes a variety of allyl alcohols to undergo nucleophilic allylation of aliphatic aldehydes and ketones at room temperature and provides homoallyl alcohols in 60-90 and ca. 60% isolated yield, respectively. The reaction is irreversible and kinetically controlled, and unique regio- and stereoselectivities observed for the allylation with unsymmetrically substituted allyl alcohols are discussed.
- Kimura, Masanari,Shimizu, Masamichi,Tanaka, Shuji,Tamaru, Yoshinao
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p. 3709 - 3718
(2007/10/03)
-
- Regioselective SN2 opening of vinylic epoxides with trialkylzincates and trialkylaluminates
-
The use of trialkylorganozincates and tetraalkylaluminates allows regioselective SN2 nucleophilic opening of vinylic epoxides. The reaction occurs with an anti-substitution pattern and can be applied to a wide range of substrates. We also show that the solvent and the structure of the epoxide have an influence on the substitution products' ratio. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.
- Equey, Olivier,Vrancken, Emmanuel,Alexakis, Alexandre
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p. 2151 - 2159
(2007/10/03)
-
- Bifunctional pyridyl alcohols with the bicyclo[3.3.0]octane scaffold in the asymmetric addition of diethylzinc to aldehydes
-
Some new pyridyl alcohols with the cis-bicyclo[3.3.0]octane scaffold were synthesized and used as chiral ligands for the enantioselective addition of diethylzinc to aldehydes. Ligands 4 were found to be far superior to the C 2-symmetric ligands
- Zhong, Yu-Wu,Jiang, Chang-Sheng,Xu, Ming-Hua,Lin, Guo-Qiang
-
p. 8861 - 8868
(2007/10/03)
-
- Towards more chemically robust polymer-supported chiral catalysts for the reactions of aldehydes with dialkylzincs.
-
N-Methyl-alpha,alpha-diphenyl-L-prolinol derivatives with para-bromo substituents in one or both of the phenyl rings are easily bound to crosslinked polystyrene beads containing phenylboronic acid residues using Suzuki reactions. When the products were used as catalysts for the reactions of aldehydes with diethylzinc in toluene at 20 degrees C, the alcohols were produced in chemical yields >90% and with ees of upto 94%. The better of the two supported catalysts gave ees only 0-9% lower than those obtained with the corresponding soluble catalyst. One of the supported catalysts was recycled successfully nine times.
- Kell, Roger J,Hodge, Philip,Nisar, Mohammad,Watson, David
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p. 1803 - 1807
(2007/10/03)
-
- Effect of InCl3 on the addition of Grignard reagents to α,β-unsaturated carbonyl compounds
-
Control of 1,2- versus 1,4-addition of organometallic reagents to enones remains a long-standing problem. There is still no satisfactory 1,2-directing agent comparable to the 1,4-directing effect of copper salts. We report that the presence of just 5 mol% indium(III) chloride can significantly alter the amount of 1,2-product formed in these reactions.
- Kelly, Brian G.,Gilheany, Declan G.
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p. 887 - 890
(2007/10/03)
-
- New polymer anchored chiral amino oxazolines as effective catalysts for enantioselective addition of diethylzinc to aldehydes
-
The application of a new type of polymer anchored chiral amino-oxazolinyl ligand as catalyst for the enantioselective addition of diethylzinc to aldehydes is reported. The catalyst is effective at a low ligand concentration and can be reused with minimal loss of activity.
- Shaikh, Nadim S,Deshpande, Vishnu H,Bedekar, Ashutosh V
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p. 5587 - 5589
(2007/10/03)
-
- Chiral ligands derived from abrine. Part 7: Effect of O, S, N in aromatic ring substituents at C-1 on enantioselectivity induced by tetrahydro-β-carboline ligands in diethylzinc addition to aldehydes
-
The effect of O, S and N atoms in aromatic ring substituents at C-1 position of tetrahydro-β-carboline ligands on the enantioselectivity of diethylzinc additions to benzaldehyde was studied when esters or tertiary alcohol functions were present at C-3. A mechanism is proposed to explain why the ester ligands 2c and 2d, in which the pyridyl N atom is at C′-2 in 2c and at C′-3 in 2d, catalyzed the addition of diethylzinc to benzaldehyde to form the (R)- and (S)-enantiomers of 1-phenyl-1-propanol, respectively. An explanation was also proposed for the moderate enantioselectivity induced by tert-alcohol 3c versus the very small enantioselectivity induced by 3d, containing a 3-pyridyl function at C-1, during diethylzinc additions. A -CH2-t-Bu substituent at C-1 leads to very high enantioselectivities.
- Zhu,Zhao,Zuo,Pittman Jr.,Dai,Hao
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p. 2613 - 2619
(2007/10/03)
-
- Synthesis of enantiopure C2-symmetric VERDI disulfonamides and their application to the catalytic enantioselective addition of diethylzinc to aromatic and aliphatic aldehydes
-
The enantiopure disulfonamides 7a-c have been prepared from the C2- symmetric diketone 2, a starting material conveniently accessible from the 'dimerization' of (+)-verbenone. These ligands, when treated with titanium isopropoxide and diethylzinc, function as catalysts for the enantioselective alkylation of aldehydes. Stereoselectivity levels ranging from 72 to 98% ee are seen depending on the structural characteristics of the aldehyde. In all cases, the absolute configuration of the carbinol product is R. A working mechanistic model is advanced for the purpose of rationalizing the high levels and direction of asymmetric induction exhibited by these VerDI catalysts.
- Paquette, Leo A.,Zhou, Renjie
-
p. 7929 - 7934
(2007/10/03)
-
- The effect of high pressure on the diastereoselectivity of intermolecular all-carbon Diels-Alder reactions
-
The influence of high pressure on the diastereoselectivity of the intermolecular all-carbon Diels-Alder reaction of the phenylbutadienes 1 a- c with the dicyanoethylenes 2a-d to give the cyclohexenes 3-8 is described. The differences in activation volume, ΔΔV(≠), for the two pathways leading to cis and trans diastereomers range from - (0.7 ± 0.8) to - (6.4 ± 0.6) cm3mol-1 indicating a pressure-induced increase of diastereoselectivity in favour of the cis adducts 3a-d, 5a-d and 7b-d.
- Tietze, Lutz F.,Henrich, Marielouise,Niklaus, Anja,Buback, Michael
-
p. 297 - 304
(2007/10/03)
-
- The Epoxy-Ramberg-Backlund reaction: A new route to allylic alcohols
-
A new variant of the Ramberg-Backlund reaction is described, the epoxy-Ramberg-Backlund reaction (ERBR), in which α,β-epoxysulfones, on treatment with base, are converted into a range of mono-, di- and tri-substituted allylic alcohols. The scope and limitations of the ERBR are discussed.
- Evans, Paul,Taylor, Richard J. K.
-
p. 3055 - 3058
(2007/10/03)
-
- Stereoselective hydrogen transfer reactions of vinyl radicals: Cyclization of alkynyl iodides by unimolecular chain transfer from silicon hydrides
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The cyclization of several substituted hexynyl and heptynyl iodides proceeds stereoselectively to give either E- or Z-exocyclic double bonds depending on the type of precursor and radical chain used, In UniMolecular Chain Transfer (UMCT) reactions, the intramolecular abstraction of hydrogen by the intermediate vinyl radical leads exclusively to the E-isomer while the traditional tin hydride method usually provides the Z-isomer with good selectivity.
- Martinez-Grau, Angeles,Curran, Dennis P.
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p. 5679 - 5698
(2007/10/03)
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- Polymer-bound palladium-catalyzed coupling of allylic alcohols with hypervalent iodonium salts
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The polymer-bound palladium catalyzed cross-coupling reaction of allylic alcohols with hypervalent iodonium sails to form carbon-carbon bonds was achieved at room temperature under extremely mild and aqueous conditions even in the absence of base with very high activity in the Stille coupling reaction. The polymeric catalyst can be easily separated from a reaction mixture and reused more than 10 times with no decrease in activity.
- Jang, Su-Bum
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p. 4421 - 4424
(2007/10/03)
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- Synthesis of a scalemic β-amino disulfide from (S)-phenylglycine and (R)-styrene oxide and use as a catalyst in enantioselective additions of diethylzinc to aldehydes
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Two routes to the novel scalemic β-amino disulfide 7 have been developed from (S)- phenylglycine and (R)-styrene oxide. The β-amino disulfide 7 was used as a catalyst in the enantioselective addition of diethylzine to aldehydes providing (R)-secondary alcohols in 39-80% ee.
- Fulton, David A.,Gibson, Colin L.
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p. 2019 - 2022
(2007/10/03)
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- On the conformational preferences of the dehydrochlorination of α-chlorosulfoxides
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Several acyclic α-chlorosulfoxides have been shown to undergo a γ-dehydrochlorination upon treatment with LDA.The proposed immediate products of γ-dehydrochlorination, thiirane-S-oxides, are unstable under the basic conditions and react further with the LDA; the isolated products are usually E-alkenes and (or) E-vinyl sulfoxides.Some of the proposed intermediate thiirane-S-oxides, compounds 6, 7, 8, and 18, were synthesized independently and treated with one equivalent of LDA in order to mimic the second step of the overall dehydrochlorination/ring opening sequence.The products obtained from the reactions of compounds 6 and 18 compared favourably with those products which were believed to arise from certain conformations of α-chlorosulfoxides 1kB and 1e, respectively.Tha addition of one equivalent of LDA to 1kA afforded a mixture containing thiirane-S-oxide 8, which is proposed as the immediate product of γ-dehydrochlorination of 1kA.The configurations of 1kB and 1hA were both shown to be threo by X-ray crystallographic studies.Those conformations which are preferred for the dehydrochlorination possess a geometry where the sulfinyl oxygen is anti to any of the substituents of the ring carbons.
- Schwan, Adrian L.,Roche, Michael R.,Gallagher, John F.,Ferguson, George
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p. 312 - 324
(2007/10/02)
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- ENANTIOSELECTIVE LIPASE-CATALYSED HYDROLYSIS OF ESTERS OF EPOXY SECONDARY ALCOHOLS: AN ALTERNATIVE TO SHARPLESS OXIDATION
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The enantioselectivity and yield of lipase-catalysed hydrolyses of epoxy butanoates (4) depends on R.Sharpless oxidation of the secondary allylic alcohol (8, R2=Pr) established that in the lipase-catalysed hydrolysis of (4, R2=Pr) th
- Marples, Brian A.,Rogers-Evans, Mark
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p. 261 - 264
(2007/10/02)
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- CHIRAL CATALYSTS FOR THE ENANTIOSELECTIVE ADDITION OF ORGANOMETALLIC REAGENTS TO ALDEHYDES
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A mechanistic model for the enantioselective addition of diethylzinc to benzaldehyde with chiral tridentate lithium complexes as catalysts correctly predicts the observed direction of enantioselectivity which occurs at levels of 85-95percent ee.
- Corey, E. J.,Hannon, Francis J.
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p. 5233 - 5236
(2007/10/02)
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