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Stereogenic Centers (stereogenic + center)
Kinds of Stereogenic Centers Selected AbstractsChemInform Abstract: Enantioselective Addition of Alkynylzinc to Arylaldehydes Catalyzed by Azetidino Amino Alcohols Bearing and Additional Stereogenic Center.CHEMINFORM, Issue 17 2010Jun-Long Niu 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: Remote Induction of Asymmetry in [13]-Macro-dilactone Topology by a Single Stereogenic Center.CHEMINFORM, Issue 4 2009W. Sean Fyvie 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] Copper-Catalyzed Preparation of Ketones Bearing a Stereogenic Center in , Position.CHEMINFORM, Issue 39 2006Darunee Soorukram 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] ChemInform Abstract: Julia,Colonna Stereoselective Epoxidation of Some ,,,-Unsaturated Enones Possessing a Stereogenic Center at the ,-Position: Synthesis of a Protected Galactonic Acid Derivative.CHEMINFORM, Issue 18 2001Peter C. Ray 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] Catalytic Enantioselective Dieckmann-Type Annulation: Synthesis of Pyrrolidines with Quaternary Stereogenic Centers,ANGEWANDTE CHEMIE, Issue 10 2010Jonathan Neues gelernt: Eine Cyclisierung vom Dieckmann-Typ ermöglichte die Synthese der Titelverbindungen mit bis zu 96,%,ee (siehe Schema; Bn=Benzyl). Das Vorliegen einer ,-koordinierenden Einheit im Substrat führt zu einer Konkurrenz zwischen Cyclisierung und Eliminierung, die durch die Art des chiralen Liganden beeinflusst wird. Eine mechanistische Erklärung für diese Beobachtungen wird vorgestellt. [source] Highly Stereoselective One-Pot Synthesis of Bicyclic Isoxazolidines with Five Stereogenic Centers by an Organocatalytic Process,ANGEWANDTE CHEMIE, Issue 33 2009Di Zhu Fünf auf einen Streich! Eine neuartige, einfache und hoch stereoselektive Synthese der Titelverbindungen wird vorgestellt, bei der fünf stereogene Zentren mithilfe eines organokatalytischen asymmetrischen Eintopf-Tandemprozesses unter Beteiligung einer diastereoselektiven intramolekularen [3+2]-Nitron-Cycloaddition kontrolliert erzeugt werden (siehe Schema). [source] ChemInform Abstract: Stereoselective Construction of Halogenated Quaternary Stereogenic Centers via Catalytic Asymmetric Diels,Alder Reaction.CHEMINFORM, Issue 35 2010Kazutaka Shibatomi No abstract is available for this article. [source] ChemInform Abstract: Rhodium(I)-Catalyzed Enantioselective Activation of Cyclobutanols: Formation of Cyclohexane Derivatives with Quaternary Stereogenic Centers.CHEMINFORM, Issue 29 2010Tobias Seiser 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(I)-Catalyzed Enantioselective Activation of Cyclobutanols: Formation of Cyclohexane Derivatives with Quaternary Stereogenic Centers.CHEMINFORM, Issue 29 2010Tobias Seiser 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] All-Carbon Quaternary Stereogenic Centers by Enantioselective Cu-Catalyzed Conjugate Additions Promoted by a Chiral N-Heterocyclic Carbene.CHEMINFORM, Issue 23 2007M. Kevin Brown 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] High Chelation Control of Three Contiguous Stereogenic Centers in the Reformatsky Reactions of Indium Enolates with ,-Hydroxy Ketones: Unexpected Stereochemistry of Lactone Formation.CHEMINFORM, Issue 46 2006Srinivasarao Arulananda Babu 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] Catalytic Enantioselective Synthesis of Quaternary All-Carbon Stereogenic Centers.CHEMINFORM, Issue 33 2005-Disubstituted, -Unsaturated Esters Through Cu-Catalyzed Asymmetric Allylic Alkylations., Preparation of Abstract For Abstract see ChemInform Abstract in Full Text. [source] Binol-Derived Monodentate Phosphites and Phosphoramidites with Phosphorus Stereogenic Centers: Novel Ligands for Transition-Metal Catalysis.CHEMINFORM, Issue 21 2005Manfred T. Reetz Abstract For Abstract see ChemInform Abstract in Full Text. [source] Diastereoselective Alkylation and Reduction of ,-Alkoxyacylsilanes: Stereoselective Construction of Three Contiguous Stereogenic Centers.CHEMINFORM, Issue 6 2004Mitsunori Honda Abstract For Abstract see ChemInform Abstract in Full Text. [source] Chiral and Flexible 2,4-Pentanediol-Tethered Cyclopropanation of Olefins with a Carbenoid Derived from a Diazo Ester to Construct Three Stereogenic Centers.CHEMINFORM, Issue 31 2003Takashi Sugimura No abstract is available for this article. [source] ChemInform Abstract: Asymmetric Trialkylaluminum Addition to Aldehydes Catalyzed by Titanium Complexes of N-Sulfonylated Amino Alcohols with Two Stereogenic Centers.CHEMINFORM, Issue 52 2001Jing-Song You 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: Reversal of Enantioselectivity Using Catalysts Containing Multiple Stereogenic Centers.CHEMINFORM, Issue 47 2001Alexander J. A. Cobb 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: Hydroxy-Group Directivity in the Regioselective and Diastereoselective [2 + 2] Photocycloaddition (Paterno,Buechi Reaction) of Aromatic Carbonyl Compounds to Chiral and Achiral Allylic Substrates: The Preparation of Oxetanes with up to Three Stereogenic Centers as Synthetic Building Blocks.CHEMINFORM, Issue 47 2001Waldemar Adam 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] P-Chirogenic Benzo-Fused Phenoxaphosphane: Synthesis, Resolution and Study of the Stereochemical Properties of the Corresponding Palladium ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2008Franco Doro Abstract The synthesis and resolution of chiral phenoxaphosphane 3, with the stereogenic center at the phosphorus atom, is described. Compound 3 has been synthesized following a well-known procedure for trapping a phosphorus atom within a six-membered ring. The resolution of the racemic mixture of 3 was achieved through separation of its diastereomeric palladacycle derivatives 7a,b and 9a,b. The absolute configuration of enantiopure phosphanes 3a,b was assigned unequivocally by means of X-ray crystal structure determination for complex 9a and by combination of NOE(1H,1H)/COSY(1H,1H) spectroscopy and DFT calculations for complexes 7a,b, which in both cases led to identical results. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Syntheses, Spectroscopic Studies, and Crystal Structures of Chiral [Rh(aminocarboxylato)(,4 -cod)] and Chiral [Rh(amino alcohol)(,4 -cod)](acetate) Complexes with an Example of a Spontaneous Resolution of a Racemic Mixture into Homochiral Helix-EnantiomersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2006Mohammed Enamullah Abstract The dimeric complex acetato(,4 -cycloocta-1,5-diene)rhodium(I), [Rh(O2CMe)(,4 -cod)]2 (cod = cycloocta-1,5-diene), reacts with amino acids [HAA = L -alanine, (S)-2-amino-2-phenylacetic acid (L -phenylglycine), N -methylglycine, and N -phenylglycine] and with the amino alcohol (S)-2-amino-2-phenylethanol to afford the aminocarboxylato(,4 -cycloocta-1,5-diene)rhodium(I) complexes [Rh(AA)(,4 -cod)] (AA = deprotonated amino acid = aminocarboxylato ligand) and [(S)-2-amino-2-phenylethanol](,4 -cycloocta-1,5-diene)rhodium(I) acetate, [Rh{(S)-HOCH2,CH(Ph)-NH2}(,4 -cod)](O2CMe) (V). The complexes are characterized by IR, UV/Vis, 1H/13C NMR and mass spectroscopy. The achiral N -phenylglycine ligand gives a chiral N -phenylglycinato complex [Rh(O2C,CH2,NHPh)(,4 -cod)] (IV) with the amine nitrogen atom becoming the stereogenic center upon metal coordination. Complex IV crystallizes in the tetragonal, chiral space group P43 and the crystal structure reveals twofold spontaneous resolution of a racemic mixture into homochiral helix-enantiomers. The investigated crystal contained only one type of helix, namely (left-handed or M- ) 43 -helical chains. This is traced first to an intermolecular N,H···O hydrogen bonding from the stereogenic amino group to a neighboring unligated carboxyl oxygen atom that connects only molecules of the same (R)-configuration into (left-handed or M- ) 43 -helical chains. This intrachain homochirality is supplemented, secondly, by the interlocking of adjacent chains with their corrugated van der Waals surface to allow for an interchain transmission of the sense of helicity, building the single crystal from the same homochiral helix-enantiomer. The enantiomeric amino alcohol complex V crystallizes in the monoclinic, noncentrosymmetric (Sohncke) space group P21. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis and Hormonal Activity of the (25S)-Cholesten-26-oic Acids , Potent Ligands for the DAF-12 Receptor in Caenorhabditis elegansEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2009René Martin Abstract Using a highly stereoselective Evans aldol reaction for the introduction of the stereogenic center at C-25, we describe an efficient synthesis of the orthogonally diprotected (25S)-26-hydroxycholesterol 11. In a few synthetic steps, this crucial intermediate 11 has been converted into the four (25S)-cholesten-26-oic acids 1,4, which have been obtained in 12,15 steps and 19,53,% overall yield based on commercially available 3,-hydroxychol-5-en-24-oic acid (5). Our biological studies of the compounds 1,4 reveal that (25S)-,7 -dafachronic acid (1) represents the most active steroidal ligand for the hormonal receptor DAF-12 in Caenorhabditis elegans. Moreover, the saturated (25S)-dafachronic acid (3) represents a new ligand for this receptor and the (25S)-steroidal acids are more active as compared to their corresponding (25R)-counterparts.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Boron-Based Diastereomerism and Enantiomerism in Imine Complexes , Determination of the Absolute Configuration at Boron by CD SpectroscopyEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 31 2008Manfred Braun Abstract Boron turns out to be a stable stereogenic center in imine complexes of aryl and alkyl boronates. Diastereomerically pure complexes 7a,c are obtained from chiral imine ligands 5a,b that are derived from the amino alcohol (R)- 4. The configuration at the boron atom is determined by crystal structure analyses. Racemic boronates 10a,c, available from a condensation of aryl boronic acids 6 with the achiral imine ligand 9, can be separated into stable enantiomers by HPLC on a chiral column. The racemization barrier ,G, has been determined to amount to 105,115 kJ,mol,1. The comparison of calculated and measured CD spectra permits to assign unambiguously the absolute configuration to boron in the enantiomeric boronate-imine complex 10a.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Convenient Synthesis of (,)-ParoxetineEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 15 2004László Czibula Abstract A convenient synthesis of the antidepressant paroxetine starting from 1-benzyl-4-piperidone (2) is reported. A stereoselective reduction resulted in cis -piperidine-3-methanol [(+)- 6]. The reaction between cis -piperidine-3-methanol mesylate (7) and sesamol led to benzyl-protected trans -paroxetine (9) through an inversion reaction of the stereogenic center at position 3. The latter compound was deprotected by hydrogenolysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] The Stereostructure of Porphyra-334: An Experimental and Calculational NMR Investigation.HELVETICA CHIMICA ACTA, Issue 3 2007Evidence for an Efficient, Proton Sponge' Abstract The mycosporine-like amino acid (MAA) porphyra-334 (1) is subjected to extensive 1H- and 13C-NMR analysis as well as to density-functional-theory (DFT) calculations. All 1H- and 13C-NMR signals of 1 are assigned, as well as the resonances of prochiral proton pairs. This is achieved by 500-MHz standard COSY, HMQC, and HMBC experiments, as well as by one-dimensional (DPFGSE-NOE) and two-dimensional (NOESY) NOE experiments. Diffusion measurements (DOSY) confirm that 1 is monomeric in D2O solution. DFT Calculations yield 13C-NMR chemical shifts which are in good agreement for species 6 which is the imino N-protonated form of 1. An exceptionally high proton affinity of 265.7,kcal/mol is calculated for 1, indicating that 1 may behave as a very powerful ,proton sponge' of comparable strength as synthetic systems studied so far. Predictions of 13C-NMR chemical shifts by the ,NMRPredict' software are in agreement with the DFT data. The absolute configuration at the ring stereogenic center of 1 is concluded to be (S) from NOE data as well as from similarities with the absolute configuration (S) found in mycosporine-glycine 16. This supports the assumption that 1 is biochemically derived from 3,3- O -didehydroquinic acid (17). The data obtained question the results recently published by a different research group claiming that the configuration at the imino moiety of 1 is (Z), rather than (E) as established by the here presented study. [source] Synthesis of Pederic Acid and Related Model StudiesHELVETICA CHIMICA ACTA, Issue 5 2004Steffen Breitfelder {[2-(Trimethylsilyl)ethoxy]methyl} (SEM)-protected pederic acid 16 was prepared by deriving the stereogenic center at C(7) from mannitol and those at C(2) and C(3) (mycalamide numbering) from trans -2,3-dimethyloxirane. Routes to pederamides involving a late oxygenation at C(7) were explored. [source] Rationalization of the stereochemistry of an addition of dialkyl phosphites to certain chiral aldimines: The experimental and theoretical approachHETEROATOM CHEMISTRY, Issue 2 2002Ryszard B. Nazarski The absolute configuration of an ,-P stereogenic center in two diastereomeric O,O-dialkyl ,-aminophosphonates (3), arising from an induced 1,3-asymmetric phosphite addition to the CN bond of furfural-derived Schiff bases (1), was established from single product 1H NMR data. Such spectra were interpreted with anisotropic shielding in relation to the AM1 and MNDO/d structures of 3; the former ones turned out to be closer to the obtained experimental results (1H NMR spectra of 3, crystallographic database study). Since favored 3-21G geometries of starting imines 1 were modeled as well, it was inferred that a stereochemical outcome of this reaction is governed by Cram selectivity. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:120,125, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10005 [source] Efficient Enantioselective Syntheses of Sertraline, 2-Epicatalponol and Catalponol from Tetralin-1,4-dioneADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Alvaro Enriquez Garcia Abstract Tetralin-1,4-dione, the stable tautomer of dihydroxynaphthalene, was reduced with catecholborane in the presence of 3,3-diphenyl-1-butyltetrahydro-3H -pyrrolo[1,2- c][1,3,2]oxazaborole as catalyst to give enantiomerically highly enriched 4-hydroxy-1-tetralone (99% ee) in an efficient one-pot procedure. The R -enantiomer provided a rapid access to sertraline while the S -enantiomer was converted into 2-epicatalponol and catalponol. A more selective enantioselective route to the antithermitic catalponol made use of the planar chiral tricarbonylchromium complex of hydroxytetralone. Its precursor chromium(tricarbonyl)[,6 -(1-4,4a,8a)-tetralin-5,8-dione] was obtained via direct complexation of 1,4-dihydroxynaphthalene using chromium(tricarbonyl)- tris(ammonia) and boron trifluoride etherate as source of the chromium(tricarbonyl) fragment. Enolate prenylation was best carried out in the presence of a tetraamine ligand. Complete inversion of the stereogenic center bearing the prenyl group of the initially obtained tetralone complex was achieved via enolate formation followed by protonation. [source] Enantioselective Electrophilic Amination of ,-Cyanothioacetates with Azodicarboxylates Catalyzed by an Axially Chiral Guanidine BaseADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 17 2009Masahiro Terada Abstract An enantioselective electrophilic amination of ,-substituted cyanothioacetates with azodicarboxylate is demonstrated using an axially chiral guanidine as a chiral Brønsted base catalyst. The corresponding product, having a quaternary stereogenic center at the ,-carbon atom, is formed in excellent enantioselectivity. [source] Synthesis of Functionalized Indoles with an ,-Stereogenic Ketone Moiety Through an Enantioselective Friedel,Crafts Alkylation with (E)-1,4-Diaryl-2-butene-1,4-dionesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Gonzalo Blay Abstract Chiral complexes of BINOL-based ligands with hafnium tert -butoxide catalyze the enantioselective Friedel,Crafts alkylation of indoles with (E)-1,4-diaryl-2-butene-1,4-diones at room temperature, with good yields and ee up to 94%. Hafnium(IV) was found to be a more effective Lewis acid than other frequently used metal ions such as titanium(IV) or zirconium(IV). Unlike the enantioselective Friedel,Crafts alkylation of indoles with ,,,-unsaturated compounds where the stereogenic center is generated in the ,-position to a carbonyl group, the Friedel,Crafts alkylation with 2-butene-1,4-diones described here generates an ,-stereogenic center with respect to one of the carbonyl groups. This can be regarded as an inversion of the normal reactivity pattern or umpolung. The enantioselective Friedel,Crafts alkylation of indoles with (E)-4-oxo-4-phenylbutenoates using a zirconium(IV)-BINOL catalyst is also reported. This reaction takes place regioselectively at the carbon in the ,-position to the ketone carbonyl group, generating an ,-ester stereogenic center. [source] Total Synthesis of (+)-RutamarinADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2008Yi-Nan Zhang Abstract The first enantioselective total synthesis of (+)-rutamarin (1) is described. The synthetic route features the highly enantioselective construction of the stereogenic center via the Sharpless asymmetric dihydroxylation (99% ee), the facile assembly of quaternary carbon-centered 3-substituted side chain and high synthetic efficiency from readily available starting materials. Furthermore, the synthetic strategy could be readily adopted for the synthesis of (+)-rutamarin analogues. [source] | ||||||||||||||||||||||||||||