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High Diastereoselectivity (high + diastereoselectivity)
Kinds of High Diastereoselectivity Selected Abstracts2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Miglena K. Georgieva Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source] Polymer-Immobilized Pyrrolidine-Based Chiral Ionic Liquids as Recyclable Organocatalysts for Asymmetric Michael Additions to Nitrostyrenes under Solvent-Free Reaction ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pinhua Li Abstract A polymer immobilized pyrrolidine-based chiral ionic liquid 5a was synthesized and was found to be a highly efficient catalyst for the Michael additions of ketones and aldehydes to nitrostyrenes, which afforded the corresponding adducts in good yields (up to 97,%), excellent enantioselectivities (up to >99,% ee) and high diastereoselectivities (up to >99:1 dr) under solvent-free reaction conditions. In addition, the catalyst 5a could be reused at least eight times without a significant loss of its catalytic activity and stereoselectivity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Unusual Magnesium Chloride Catalyzed Non-Evans anti -Aldol Reactions of an Enolizable L -Threose DerivativeEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 34 2007James McNulty Abstract The magnesium chloride catalyzed anti -aldol reaction of phenyl acetate derived oxazolidinones proceeds readily with enolizable L -threose derivative 8 to provide anti -aldol adducts in high yields and with very high diastereoselectivities. The reaction is also efficient with aromatic aldehydes and provides slightly lower diastereoselectivities. This extension allows access to stereochemically defined fragments applicable to the synthesis of alkaloid and phenylpropanoid derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Highly Enantio- and Diastereoselective One-Pot Reactions in Aqueous Media: Combined Asymmetric Rh-Catalyzed Conjugate Addition/Metal-Mediated AllylationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006Sara Källström Abstract 1,3-Disubstituted, enantiopure cyclohexanols have been prepared in very high diastereoselectivities and good yields by a concise one-pot method combining the enantioselective rhodium-catalyzed conjugate addition of arylboronic acids with indium-mediated allylation into a highly efficient one-pot reaction in aqueous media. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Asymmetric Mannich-Type Reaction of a Chiral N -(tert -Butylsulfinyl) Ketimine with Imines: Application to the Synthesis of Chiral 1,3-DiaminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2006Cui-Hua Zhao Abstract Deprotonation of the chiral N -(tert -butylsulfinyl) ketimine 1 followed by trapping with imines 2 afforded the ,-aminoimines 3 as the Mannich-type products in high diastereoselectivities (99:1 dr). As versatile synthons chiral ,-amino imines 3 could be transformed into enantiomeric ,-amino ketone and chiral syn - or anti -1,3-diamines with high diastereomeric excess by hydrolysis or reduction, respectively. Moreover, the nucleophilic addition of organometallicreagents to chiral ,-amino imines 3 could provide 1,1,3-trisubstituted 1,3-diamines with high diastereoselectivities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Diastereoselective Reactions of the Tiglic Acid Functionality Mediated by Oxazolidine Chiral Auxiliaries: A Mechanistic Comparison of DMD andm -CPBA Epoxidations versus Singlet Oxygen and PTAD Ene ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2005Aurelia Pastor Abstract 2,2-Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastereoselective functionalization of the optically active tiglic acid derivatives (S)- 1 by means of epoxidation with DMD or m -CPBA and ene reactions with 1O2 or PTAD. In the DMD and m -CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection were observed. In contrast, the stereochemistry of the 1O2 and PTAD ene reactions depended on the size of the attacking enophile: whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 1O2. The stereochemical results for the DMD and m -CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects. The PTAD ene reaction for these tiglic acids (S)- 1 provides, after removal of the chiral auxiliaries, an attractive synthetic route for optically active ,-amino acid derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Highly Efficient Asymmetric Michael Reaction of Aldehydes to Nitroalkenes with Diphenylperhydroindolinol Silyl Ethers as OrganocatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Ren-Shi Luo Abstract New dihydroindole and perhydroindole derivatives were synthesized in good yields and evaluated as chiral catalysts in the asymmetric Michael reaction of aldehydes to nitroalkenes. (2S,3aS,7aS)-Diphenylperhydroindolinol silyl ether 10 facilitated the reaction of a wide range of aldehyde and nitroalkene substrates, providing Michael adducts in nearly optically pure form (99% ee), good yields and high diastereoselectivities (syn/anti up to 99:1). These results show for the first time that perhydroindole derivatives can also be highly efficient organocatalysts for the asymmetric Michael reaction, exhibiting comparable or even better enantioselectivities than proline derivatives. [source] Addition of Azomethine Ylides to Aldehydes: Mechanistic Dichotomy of Differentially Substituted ,-Imino EstersEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2010Brinton Seashore-Ludlow Abstract The formal 1,3-dipolar cycloaddition of azomethine ylides and aldehydes is explored, as hydrolysis of the resulting oxazolidine product gives facile access to valuable syn -,-aryl-,-hydroxy-,-amino esters. The use of using benzaldehyde-derived imines as the ylide precursor results in 1,3-dipolar cycloaddition with high conversions but low diastereoselectivity. In contrast, the employment of benzophenone-derived imines as the ylide precursor results in an aldol reaction, which gives the intermediate oxazolidine in high diastereoselectivity and requires a weak acid catalyst to achieve higher conversions. [source] Ring Expansion versus Cyclization in 4-Oxoazetidine-2- carbaldehydes Catalyzed by Molecular Iodine: Experimental and Theoretical Study in ConcertADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Benito Alcaide Abstract Molecular iodine (10,mol%) efficiently catalyzes the ring expansion of 4-oxoazetidine-2-carbaldehydes in the presence of tert -butyldimethylsilyl cyanide, or allylic and propargylic trimethylsilanes to afford protected 5-functionalized-3,4-dihydroxypyrrolidin-2-ones with good yield and high diastereoselectivity, through a C3C4 bond cleavage of the ,-lactam nucleus. Interestingly, in contrast to the iodine-catalyzed reactions of 3-alkoxy-,-lactam aldehydes which lead to the corresponding ,-lactam derivatives (rearrangement adducts), the reactions of 3-aryloxy-,-lactam aldehydes under similar conditions gave ,-lactam-fused chromanes (cyclization adducts) as the sole products, through exclusive electrophilic aromatic substitution involving the C3 aromatic ring and the carbaldehyde. In order to support the mechanistic proposals, theoretical studies have been performed. [source] A Highly Diastereoselective Tertiary Amine-Catalyzed Cascade Michael,Michael,Henry Reaction between Nitromethane, Activated Alkenes and ,,,-Unsaturated Carbonyl CompoundsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1 2010Bo Zhang Abstract A new tertiary amine-catalyzed cascade Michael,Michael,Henry reaction between nitromethane, a doubly activated alkene and an ,,,-unsaturated carbonyl compound is described, which provides a convenient and efficient synthesis for densely functionalized cyclohexanes and some bicyclic compounds in moderate to excellent yields with high diastereoselectivity. [source] The Use of Samarium Enolates, A Novel Alternative in the Addition Reactions to Imines.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 20094-Diamino Esters, Amides, Enantiopure , Synthesis of 3-Amino Esters Abstract An efficient reaction of tosylimines with a range of samarium enolates (derived from esters, and amides) is reported. The reaction with the ,-dibenzylamino- N - tert- butanesulfinimine derived from chiral phenylalaninal afforded the corresponding enantiopure 3,4-diamino ester with very high diastereoselectivity. [source] Efficient Stereoselective Synthesis of Nitrocyclopropanes by the Oxidative Cyclization of Michael Adducts of Nitroolefins with Activated Methylene CompoundsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2008Renhua Fan Abstract An efficient oxidative cyclopropanation of the Michael adducts of nitroolefins with activated methylene compounds by the combination of iodobenzene diacetate and tetrabutylammonium iodide is reported. Highly functionalized nitrocyclopropanes are synthesized in moderate to good yields via the Michael addition and cyclopropanation with high diastereoselectivity and enantioselectivity under mild conditions. [source] Aqueous Asymmetric Mukaiyama Aldol Reaction Catalyzed by Chiral Gallium Lewis Acid with Trost-Type Semi-Crown LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2005Hui-Jing Li Abstract The combination of Ga(OTf)3 with chiral semi-crown ligands (1a,e) generates highly effective chiral gallium Lewis acid catalysts for aqueous asymmetric aldol reactions of aromatic silyl enol ethers with aldehydes. A ligand-acceleration effect was observed. Water is essential for obtaining high diastereoselectivity and enantioselectivity. The p -phenyl substituent in aromatic silyl enol ether (2,h) plays an important role and increases the enantioselectivity up to 95% ee. Although aliphatic silyl enol ethers provided low enantioselectivities and silylketene acetal is easily hydrolyzed in aqueous alcohol, the aldol reactions of silylketene thioacetal (12) with aldehydes in the presence of gallium-Lewis acid catalysts give the ,-hydroxy thioester with reasonable yields and high diastereo- (up to 99,:,1) and enantioselectivities (up to 96% ee). [source] 1-(,-Aminobenzyl)-2-naphthol: A New Chiral Auxiliary for the Synthesis of Enantiopure ,-Aminophosphonic AcidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2009Kirill Abstract Ooh Betti! A new diastereoselective synthesis of ,-aminophosphonates has been developed based on the reaction of trialkyl phosphites with chiral imines derived from (R)- or (S)-1-(,-aminobenzyl)-2-naphthol (Betti base; see scheme, X=H, CH3, or Br). The reaction proceeds with high diastereoselectivity. Treatment with HCl results in the formation of the desired ,-aminophosphonic acids. A new diastereoselective synthesis of ,-aminophosphonates has been developed, based on the reaction, in the presence of trifluoroacetic acid, of trialkyl phosphites with chiral imines derived from (R)- or (S)-1-(,-aminobenzyl)-2-naphthol. The reaction proceeds at room temperature in toluene with high diastereoselectivity. The major diastereomer can be separated by crystallization from an appropriate solvent. The relative configuration of both chiral centers of the major diastereomer was determined by single-crystal X-ray structure analysis. The desired ,-aminophosphonic acids can be obtained in enantiopure form by treatment of the corresponding diastereomers with HCl. [source] Asymmetric Sulfonium Ylide Mediated Cyclopropanation: Stereocontrolled Synthesis of (+)-LY354740CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2006Varinder K. Aggarwal Prof. Abstract The reaction of ester-stabilized sulfonium ylides with cyclopentenone to give (+)- 5 ((1S,5R,6S)-ethyl 2-oxobicyclo[3.1.0]hexane-6-carboxylate), an important precursor to the pharmacologically important compound (+)-LY354740, has been studied using chiral sulfides operating in both catalytic (sulfide, Cu(acac)2, ethyl diazoacetate, 60,°C) and stoichiometric modes (sulfonium salt, base, room temperature). It was found that the reaction conditions employed had a major influence over both diastereo- and enantioselectivity. Under catalytic conditions, good enantioselectivity with low diastereoselectivity was observed, but under stoichiometric conditions low enantioselectivity with high diastereoselectivity was observed. When the stoichiometric reactions were conducted at high dilution, diastereoselectivity was reduced. This indicated that base-mediated betaine equilibration was occurring (which is slow relative to ring closure at high dilution). Based on this model, conditions for achieving high enantioselectivity were established as follows: use of a preformed ylide, absence of base, hindered ester (to reduce ylide-mediated betaine equilibration), and low concentration. Under these conditions high enantioselectivity (95,% ee) was achieved, albeit with low diastereocontrol. Our model for selectivity has been applied to other sulfonium ylide mediated cyclopropanation reactions and successfully accounts for the diastereoselectivity observed in all such reported reactions to date. [source] Vinyl Sulfoxides as Stereochemical Controllers in Intermolecular Pauson,Khand Reactions: Applications to the Enantioselective Synthesis of Natural CyclopentanoidsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2004Marta Rodríguez Rivero Abstract The use of sulfoxides as chiral auxiliaries in asymmetric intermolecular Pauson,Khand reactions is described. After screening a wide variety of substituents on the sulfur atom in ,,,-unsaturated sulfoxides, the readily available o -(N,N -dimethylamino)phenyl vinyl sulfoxide (1,i) has proved to be highly reactive with substituted terminal alkynes under N -oxide-promoted conditions (CH3CN, 0,°C). In addition, these Pauson,Khand reactions occurred with complete regioselectivity and very high diastereoselectivity (de=86,>96,%, (S,RS) diastereomer). Experimental studies suggest that the high reactivity exhibited by the vinyl sulfoxide 1,i relies on the ability of the amine group to act as a soft ligand on the alkyne dicobalt complex prior to the generation of the cobaltacycle intermediate. On the other hand, both theoretical and experimental studies show that the high stereoselectivity of the process is due to the easy thermodynamic epimerization at the C5 center in the resulting 5-sulfinyl-2-cyclopentenone adducts. When it is taken into account that the known asymmetric intermolecular Pauson,Khand reactions are limited to the use of highly reactive bicyclic alkenes, mainly norbornene and norbornadiene, this novel procedure constitutes the first asymmetric version with unstrained acyclic alkenes. As a demonstration of the synthetic interest of this sulfoxide-based methodology in the enantioselective preparation of stereochemically complex cyclopentanoids, we have developed very short and efficient syntheses of the antibiotic (,)-pentenomycin I and the (,)-aminocyclopentitol moiety of a hopane triterpenoid. Se ha estudiado la utilización de sulfóxidos como auxiliares quirales en reacciones de Pauson,Khand intermoleculares. Tras considerar una amplia variedad de vinil sulfóxidos diferentemente sustituidos en el átomo de azufre, se ha encontrado que el o -(N,N -dimetilamino)fenil sulfóxido (1,i) presenta una elevada reactividad frente a alquinos terminales en reacciones de Pauson,Khand. Además, estas reacciones transcurren con regioselectividades completas y diastereoselectividades muy elevadas (ed=86,>96,%). Estudios teóricos y experimentales sugieren que la gran reactividad mostrada por el vinil sulfóxido 1,i se debe a la capacidad del grupo amino para coordinarse al complejo de dicobalto del alquino, favoreciendo así la posterior formación del cobaltaciclo intermedio. Por otro lado, estudios tanto teóricos como experimentales han demostrado que la elevada diastereoselectividad del proceso es consecuencia de la fácil epimerización termodinámica en la posición C-5 de las 5-sulfinil-2-ciclopentenonas finales. Teniendo en cuenta que hasta el momento la reacción de Pauson,Khand intermolecular estaba limitada al empleo de alquenos bicíclicos muy reactivos, principalmente norborneno y norbornadieno, este nuevo procedimiento constituye la primera versión asimétrica con alquenos acíclicos no tensionados. Como demostración de la utilidad sintética de esta nueva metodología en la preparación enantioselectiva de sistemas ciclopentánicos complejos, se han desarrollado síntesis muy eficaces del antibiótico (,)-pentenomicina I y de la unidad de aminociclopentitol de un triperpenoide. [source] Asymmetric pinacol coupling of aromatic aldehydes catalyzed by TiCl4(THF)2 -Zn/chiral diaminesCHINESE JOURNAL OF CHEMISTRY, Issue 10 2003You-Gui Li Abstract Asymmetric pinacol coupling of aromatic aldehydes catalyzed by chiral diamines/low-valent titanium complexes gave corresponding pinacols in good yields with high diastereoselectivity and moderate enantioselectivities. [source] | ||||||||||||||||||||||