Chiral Auxiliary (chiral + auxiliary)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Chiral Auxiliary

  • new chiral auxiliary


  • Selected Abstracts


    2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical Approach

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010
    Miglena 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]


    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 Reactions

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2005
    Aurelia 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]


    New S,O-Acetals from (1R)-(-)-Myrtenal as Chiral Auxiliaries in Nucleophilic Additions.

    CHEMINFORM, Issue 24 2004
    Luis Chacon-Garcia
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    Synthesis of Optically Pure Arylsilylcarbinols and Their Use as Chiral Auxiliaries in Oxacarbenium Ion Reactions.

    CHEMINFORM, Issue 21 2004
    John R. Huckins
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    A General Method for the Asymmetric Synthesis of Both Enantiomers of 1-Substituted 1,2,3,4-Tetrahydro-,-carbolines Employing Pyroglutamic Acid Derivatives as Chiral Auxiliaries.

    CHEMINFORM, Issue 37 2003
    Takashi Itoh
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    ChemInform Abstract: O-Silylated Steroidal cis-Amino Alcohols as Chiral Auxiliaries: Highly Diastereoselective Pd-Catalyzed Cyclopropanation of ,,,-Unsaturated Aldimines.

    CHEMINFORM, Issue 29 2002
    M. Dubs
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    ChemInform Abstract: The Influence of Chiral Auxiliaries is Enhanced Within Zeolites

    CHEMINFORM, Issue 3 2001
    Sivaguru Jayaraman
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    ChemInform Abstract: New Chiral Auxiliaries for Highly Stereoselective Asymmetric Methoxyselenenylations.

    CHEMINFORM, Issue 1 2001
    Thomas G. Back
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    Preparation of ,2 -Amino Acid Derivatives (,2hThr, ,2hTrp, ,2hMet, ,2hPro, ,2hLys, Pyrrolidine-3-carboxylic Acid) by Using DIOZ as Chiral Auxiliary,

    HELVETICA CHIMICA ACTA, Issue 8 2005
    Francois Gessier
    The title compounds were prepared from valine-derived N -acylated oxazolidin-2-ones, 1,3, 7, 9, by highly diastereoselective (,,90%) Mannich reaction (,,4,6; Scheme,1) or aldol addition (,,8 and 10; Scheme,2) of the corresponding Ti- or B-enolates as the key step. The superiority of the ,5,5-diphenyl-4-isopropyl-1,3-oxazolidin-2-one' (DIOZ) was demonstrated, once more, in these reactions and in subsequent transformations leading to various t -Bu-, Boc-, Fmoc-, and Cbz-protected ,2 -homoamino acid derivatives 11,23 (Schemes,3,6). The use of , -bromo-acyl-oxazolidinones 1,3 as starting materials turned out to open access to a variety of enantiomerically pure trifunctional and cyclic carboxylic-acid derivatives. [source]


    ChemInform Abstract: Axial Chirality Control During Suzuki,Miyaura Cross-Coupling Reactions: The tert-Butylsulfinyl Group as an Efficient Chiral Auxiliary.

    CHEMINFORM, Issue 13 2010
    Francoise Colobert
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    ChemInform Abstract: Rhodium-Catalyzed Reformatsky-Type Reaction for Asymmetric Synthesis of Difluoro-,-lactams Using Menthyl Group as a Chiral Auxiliary.

    CHEMINFORM, Issue 36 2008
    Atsushi Tarui
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    1-(2,4,6-Triisopropylphenyl)ethylamine: A New Chiral Auxiliary for the Asymmetric Synthesis of ,-Amino Acid Derivatives.

    CHEMINFORM, Issue 21 2007
    Pascale Cividino
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Application of Axially Dissymmetric Ligand Recoverable with Fluorous Solvent as a Chiral Auxiliary.

    CHEMINFORM, Issue 20 2006
    Masaaki Omote
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Enantioselective Phenyl Transfer to Aldehydes Using 1,1,-Bi-2-Naphthol-3,3,-dicarboxamide as Chiral Auxiliary.

    CHEMINFORM, Issue 51 2005
    Katsuji Ito
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    A New Entry to Asymmetric Synthesis of Optically Active ,,,-Substituted ,-Butyrolactones, Using a Carbohydrate Derived Amide as Both a Chiral Auxiliary and a Proton Source.

    CHEMINFORM, Issue 24 2005
    Ling-Lin Huang
    No abstract is available for this article. [source]


    Diastereoselective Heterogeneous Catalytic Hydrogenation of 2-Methyl Nicotinic Acid Using Pyroglutamate Chiral Auxiliary.

    CHEMINFORM, Issue 52 2003
    Najiba Douja
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    An Inexpensive Carbohydrate Derivative Used as a Chiral Auxiliary in the Synthesis of ,-Hydroxy Carboxylic Acids.

    CHEMINFORM, Issue 5 2003
    Hongwu Yu
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    NaBH4 -MnCl2 for Improved Reduction of ,-Keto Esters Attached to a Chiral Auxiliary.

    CHEMINFORM, Issue 52 2002
    Comparison with Zn(BH4)2.
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    ChemInform Abstract: Preparation of Both Enantiomers of 1-Allyl-1,2,3,4-tetrahydro-,-carboline Using Allyltin Reagents and a Chiral Auxiliary Derived from L-Proline.

    CHEMINFORM, Issue 1 2002
    Takashi Itoh
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    1-(,-Aminobenzyl)-2-naphthol: A New Chiral Auxiliary for the Synthesis of Enantiopure ,-Aminophosphonic Acids

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 27 2009
    Kirill
    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]


    2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical Approach

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010
    Miglena 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]


    Stereogenic Evolution of clasto -Lactacystin ,-Lactone from L -Serine

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2007
    Cheol H. Yoon
    Abstract Reported herein is a novel synthesis of clasto -lactacystin ,-lactone. The ,-lactam core was selectively prepared by an intramolecular C,H insertion to establish the stereocenter, C(6). The ensuing construction of the quaternary C(5) and carbinol C(9) centers was facilitated by aldol with excellent stereoselection. All these new stereochemistries were induced by the inherent chirality of L -serine without employing chiral auxiliaries or reagents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [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 Reactions

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2005
    Aurelia 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]


    Asymmetric biomimetic oxidations of phenols using oxazolidines as chiral auxiliaries: the enantioselective synthesis of (+)- and (,)-dehydrodiconiferyl alcohol,

    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 8-9 2006
    Maurizio Bruschi
    Abstract Stereoselective bimolecular radical coupling reactions of phenylpropenoid phenols are described. Evans's 2-oxazolidinone 11a,d derivatives of ferulic acid were prepared and oxidized to give dimeric benzofuran neolignan structures 12,13a,d in 40,50% overall yields. The chiral phenols were dimerized either enzymatically with hydrogen peroxide and horseradish peroxidase (HRP) or with silver oxide. The enantioselectivity after reductive cleavage of the chiral auxiliaries to give dehydrodiconiferyl alcohol ranged from 18% to 62% enantiomeric excess. The conformational analysis and the activation energy using semiempirical PM3 calculations on the intermediate quinomethides is used to explain the observed stereoselectivity. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    Asymmetric Allylation of Methyl Ketones by Using Chiral Phenyl Carbinols

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2009

    Abstract To methyl or to alkyl? High induced facial selectivities and excellent yields are obtained in the allylation of aliphatic methyl ketones by using a structurally simple phenylbenzyl auxiliary to give the corresponding homoallylic ethers (see scheme). The transferred auxiliary has a very good protecting quality and can easily be removed. Novel chiral auxiliaries for the stereoselective allylation of aliphatic methyl ketones with allyltrimethylsilane and their use in the synthesis of homoallylic ethers are described. In a multicomponent domino process catalyzed by trifluoromethanesulfonic acid, the allyl moiety and the auxiliary are transferred onto the substrate to yield tertiary homoallylic ethers. The most useful auxiliary for a general application turned out to be the trimethylsilyl ether of phenyl benzyl carbinol with an induced diastereoselectivity of 90:10 using ethyl methyl ketone and 94:6 using isopropyl methyl ketone as substrates. The transferred substituted benzyl moiety has good protecting properties in subsequent transformations and can easily be removed under reductive conditions to provide the corresponding homoallylic alcohol. The origin of the high selectivity could be elucidated by identifying the relevant transition states using quantum-chemical calculations. An excellent agreement between calculated and experimentally observed selectivities was obtained assuming an oxocarbenium ion as intermediate. [source]


    Iodine Monochloride,Amine Complexes: An Experimental and Computational Approach to New Chiral Electrophiles

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2005
    Jürgen Haas Dr.
    Abstract Lactonizations are important steps in many synthetic sequences. Substrate-controlled reactions that use chiral auxiliaries or chiral alkenes have already been studied in depth. This study focuses on stereoselective reagent-controlled iodolactonizations, by application of a new method that uses complexes of iodine monochloride and various donor molecules. (R)-1,2,3,4-Tetrahydro-1-naphthylamine and other amines with similar structures were found to be efficient in the iodocyclization of 4-aryl-4-pentenoic acids. Calculations were performed on complexes of (R)-1,2,3,4-tetrahydro-1-naphthylamine with XCl (X=I, H) to identify possible reactive species in these iodocyclizations. Calculations were carried out at various levels of theory, including B3,LYP/6-31+G (d,p) by using a modified SDD basis set for iodine. [source]


    Vinyl Sulfoxides as Stereochemical Controllers in Intermolecular Pauson,Khand Reactions: Applications to the Enantioselective Synthesis of Natural Cyclopentanoids

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2004
    Marta 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 Epoxidation of Terminal Olefins with Binaphthyl Strapped Porphyrin Catalysts: (-( Stacking Interaction and Steric Effects on the Enantioselectivities

    CHINESE JOURNAL OF CHEMISTRY, Issue 5 2009
    Qizhi REN
    Abstract Two binaphthyl strapped porphyrins with similar chiral auxiliaries 1b and 2b were used as efficient catalysts for asymmetric epoxidation of both styrene derivatives and non-aromatic olefin substrates. Theoretical calculation of styrene approach to both catalysts has been performed. The subtle difference of the chiral cavities between two porphyrins has been analyzed by 1H NMR. The ,-, stacking interaction between aromatic substrates and catalysts might be one factor for the dramatic different enantioselectivities. Besides, the steric effect of the binaphthyl handle of 1b and 2b also causes the high ee values for non-aromatic olefin epoxidations. [source]


    Tetra- tert -butyltrioxabicyclo[3.3.1]nonadienedicarboxylic Acid: Optical Resolution, Absolute Configuration and Application in Chiral Discrimination

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2008
    Jennifer Kremsner
    Abstract The enantiopure bridged bis-dioxine 4, a dissymmetric dicarboxylic acid exhibiting axial chirality, can easily be synthesized and serve as host for separating and/or transporting chiral guest molecules. Racemic 4 gives with (R)- and (S)-1-phenylethylamine the corresponding pure diastereomeric salts 7 and 8. The absolut configuration of the diacid 4 in the diastereomeric salt 7 containing (R)-1-phenylethylamine was confirmed to be R by X-ray crystal structure analysis, which also confirmed its concave nature. Release of the acid-sensitive pure enantiomers (R)- 4 as well as (S)- 4 was achieved conveniently by use of dry flash-chromatography on silica. The CD spectrum shows a positive Cotton effect of the (S)-enantiomer at 206 nm. The enantiomeric purity was proved by 1H NMR discrimination of the diastereomeric salts with (R,R)-1,2-bis(4-methoxyphenyl)ethane-1,2-diamine as the base. The dicarboxylic acid (R)- 4 can be used as chiral auxiliary as demonstrated by the difficult resolution of racemicN,N,-di- tert -butyl-1,2-bis(4-methoxyphenyl)ethane-1,2-diamine 9.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]


    Synthesis of Enantiopure 1-Aryl-1-butylamines and 1-Aryl-3-butenylamines by Diastereoselective Addition of Allylzinc Bromide to Imines Derived from (R)-Phenylglycine Amide

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2004
    Jan Dalmolen
    Abstract The synthesis of enantiopure 1-aryl-1-butylamines via a highly diastereoselective addition of allylzinc bromide to imines derived from (R)-phenylglycine amide is reported. These are synthesised by a three-step procedure, which involves: (a) formation of the chiral imines; (b) asymmetric addition of the allylzinc reagent; (c) removal of the chiral auxiliary by means of a reductive or non-reductive method. The reductive method provides 1-aryl-1-butylamines whereas the non-reductive method preserves the double bond to afford 1-aryl-3-butenylamines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]