- Diastereoselective 'contra-Michael' addition of (-)- sparteine/organolithium complexes to secondary chiral cinnamyl amides
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'Contra-Michael' addition of (-)sparteine/organolithium reagents complexes to cinnamyl secondary amides derived from (R) or (S)-α- Methylbenzylamine occurs with matched or mismatched pairs, and allows an enantioselective access to 2-benzyl-amides,- acids,
- Bremand, Nathalie,Marek, Ilan,Normant, Jean F.
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- Pseudoephenamine: A practical chiral auxiliary for asymmetric synthesis
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Unrestricted: Pseudoephenamine is introduced as a versatile chiral auxiliary and an alternative to pseudoephedrine in asymmetric synthesis. It is free from regulatory restrictions and leads to remarkable stereocontrol in alkylation reactions, especially in those that form quaternary carbon centers. Amides derived from pseudoephenamine exhibit a high propensity to be crystalline substances, and provide sharp, well-defined signals in NMR spectra. Copyright
- Morales, Marvin R.,Mellem, Kevin T.,Myers, Andrew G.
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supporting information; experimental part
p. 4568 - 4571
(2012/06/30)
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- Structural requirements for substrate in highly enantioselective hydrogenation over the cinchonidine-modified Pd/C
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Relationship between substrate structure and enantioselectivity is studied for the asymmetric hydrogenation of 42 different (E)-α, β-disubstituted acrylic acids (propenoic acids) over cinchonidine-modified Pd/C. The β-phenyl group is indispensable for high enantioselectivity of α-phenylcinnamic acid (2,3-diphenylpropenoic acid, 81% ee), and substitution on this group affects markedly the selectivity. The high ee up to 92% was achieved by the β - p-alkoxyphenyl substitution, and the selectivity is ascribed mainly to stronger interaction of the substrate with the chiral modifier on the catalyst surface. In contrast, substitution on the α-phenyl group does not affect notably the enantioselectivity (80-82% ee) or even the α-phenyl group itself is not indispensable but replaceable with a properly bulky group for the high enantioselectivity.
- Sugimura, Takashi,Uchida, Takayuki,Watanabe, Junya,Kubota, Takeshi,Okamoto, Yasuaki,Misaki, Tomonori,Okuyama, Tadashi
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experimental part
p. 57 - 64
(2009/06/17)
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- A cleavable linker strategy for optimising enolate alkylation reactions of a polymer-supported Evans' oxazolidin-2-one
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A cleavable linker strategy has been used to optimise the enolate alkylation reactions of a recyclable l-tyrosine derived polymer-supported oxazolidin-2-one for the asymmetric synthesis of a series of chiral α-alkyl acids. The Royal Society of Chemistry.
- Green, Rachel,Merritt, Andrew T.,Bull, Steven D.
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p. 508 - 510
(2008/09/20)
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- An easy access to enantio-enriched α-substituted aldehydes by carbolithiation of β-phenyl or β-silyl-α,β-ethylenic aldehydes, protected with the monolithioamide of a chiral diamine
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Lithium amide derived from N,N,N′-trimethyl-1,2-diphenylethanediamine converts cinnamaldehyde to a lithium alkoxyamide which undergoes a regio- and stereoselective carbolithiation upon addition of various organolithiums. Subsequent hydrolysis or trapping with MeI delivers α-mono-, or α,β-disubstituted 3-phenylpropanals with e.e.s of 76-96%. Extension to a silylated α-enal is possible.
- Brémand, Nathalie,Mangeney, Pierre,Normant, Jean F.
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p. 1883 - 1885
(2007/10/03)
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- Regioselective addition of nbutyllithium on secondary cinnamyl amides: 'Michael' versus 'contra-Michael' process
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Lithiated secondary cinnamyl amides undergo a preferred 'contra-Michael' addition of nbutyllithium, complexed with (-)sparteine, in a non polar solvent.
- Bremand, Nathalie,Marek, Ilan,Normant, Jean F.
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p. 3379 - 3382
(2007/10/03)
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- Enantioselective carbometalation of cinnamyl derivatives: New access to chiral disubstituted cyclopropanes - Configurational stability of benzylic organozinc halides
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A stoichiometric or catalytic amount of (-)-sparteine can serve asa promoter for the enantioselective carbolithiation of cinnamyl derivatives by primary and secondary organolithium compounds. The enantiofacial choice of the addition reaction is dependent on the stereochemistry of the initial double bond. The resulting benzylic organolithium compounds can be derivatized to a linear phenylated chain that bears two contiguous stereogenic centers with given configurations. The use of the dimethyl acetal of the (E)-cinnamyl alcohol allows the highest enantioselective carbolithiation and by simply warming the reaction mixture to room temperature, the resulting benzylic organo-lithium intermediate undergoes a 1,3-elimination to give the chiral disubstituted cyclopropane in high enantiomeric excess (90-95% ee). Another significant finding is the observation that the Li-Zn transmetalation in a benzylic species occurs with inversion of configuration, and the corresponding acyclic benzylic zinc halides have observable configurational stability at - 30°C.
- Norsikian, Stephanie,Marek, Ilan,Klein, Sophie,Poisson, Jean F.,Normant, Jean F.
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p. 2055 - 2068
(2007/10/03)
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- Synthesis of optically active allenyltitaniums having axial chirality by the reaction of optically active propargylic compounds with a Ti(O-i-Pr)4/2i- PrMgCl reagent
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The reaction of a titanium(II) complex (η2-propene)Ti(O-i-Pr)2, generated in situ from Ti(O-i-Pr)4 and 2 equiv of i-PrMgCl, with optically active secondary propargyl phosphate and tertiary propargyl carbonate proceeds with more than 97% chiral transfer, thus providing an efficient and practical method for synthesizing di- and tri-substituted allenyltitaniums with high optical purity.
- Okamoto, Sentaro,An, Duk Keun,Sato, Fumie
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p. 4551 - 4554
(2007/10/03)
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- Pseudoephedrine as a practical chiral auxiliary for the synthesis of highly enantiomerically enriched carboxylic acids, alcohols, aldehydes, and ketones
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The use of pseudoephedrine as a practical chiral auxiliary for asymmetric synthesis is described in full. Both enantiomers of pseudoephedrine are inexpensive commodity chemicals and can be N-acylated in high yields to form tertiary amides. In the presence of lithium chloride, the enolates of the corresponding pseudoephedrine amides undergo highly diastereoselective alkylations with a wide range of alkyl halides to afford α-substituted products in high yields. These products can then be transformed in a single operation into highly enantiomerically enriched carboxylic acids, alcohols, aldehydes, and ketones.
- Myers, Andrew G.,Yang, Bryant H.,Chen, Hou,McKinstry, Lydia,Kopecky, David J.,Gleason, James L.
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p. 6496 - 6511
(2007/10/03)
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- Diastereoselektive Kupplung anodish erzeugter Radikale mit chiralen Amidgruppen
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Stichworte: Asymmetrische Synthesen * Auxiliare * Kolbe-Elektrolyse * Radikale
- Klotz-Berendes, Bruno,Schaefer, Hans J.,Grehl, Matthias,Froehlich, Roland
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p. 218 - 220
(2007/10/02)
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- Enantioselective aldol chemistry via alkyl enol ethers. Scope of the Lewis acid catalyzed condensation of optically active trimethylsilyl and methyl 2-[(E)-1-alkenyloxy]ethanoates with acetals
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Optically active, mono- and disubstituted trimethylsilyl 2-[(E)-1-alkenyloxy]ethanoates of the type RR1CH = CHOCHR2CO2SiMe3 (R = Me, PhCH2, n-Bu, MeO2CCMe2CH2, PhSCHs
- Faunce, James A.,Grisso, Bryan A.,Mackenzie, Peter B.
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p. 3418 - 3426
(2007/10/02)
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- Asymmetric Synthesis Using Chiral Piperazine. I. Asymmetric Synthesis of 2-Substituted Alcohol and Carboxylic Acid by Diastereoselective Alkylation of Chiral Diamides Derived from Piperazines
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The diastereoselective alkylation of chiral diamides derived from chiral piperazines afforded optically active alcohols and acids in moderate enantiomeric excesses (up to 68percent e.e.).
- Soai, Kenso,Hayashi, Hiroshi,Shinozaki, Akihiro,Umebayashi, Hideaki,Yamada, Yasuyuki
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p. 3450 - 3452
(2007/10/02)
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