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Quaternary Center (quaternary + center)
Kinds of Quaternary Center Selected AbstractsA Concise Formal Synthesis of Diazonamide,A by the Stereoselective Construction of the C10 Quaternary Center,ANGEWANDTE CHEMIE, Issue 13 2010Cheng-Kang Mai Schutzgruppen überschätzt! Der Schlüsselschritt einer formalen Totalsynthese von Diazonamid,A ist die intramolekulare SNAr-Reaktion zwischen einem Oxindol und einem Bromoxazol. Interessanterweise verläuft diese Reaktion am besten, wenn das Oxindol-Stickstoffatom und die Phenolgruppe der Cyclisierungsvorstufe keine Schutzgruppen tragen und die milde Base Na2CO3 eingesetzt wird. [source] Two-Step Formal [3 + 2] Cycloaddition of Enones/Enals and Allenyl MOM Ether: Gold-Catalyzed Highly Diastereoselective Synthesis of Cyclopentanone Enol Ether Containing an All-Carbon Quaternary Center.CHEMINFORM, Issue 39 2007Xiaogen Huang 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: Catalytic Asymmetric Domino Michael,Henry Reaction: Enantioselective Access to Bicycles with Consecutive Quaternary Centers by Using Bifunctional Catalysts.CHEMINFORM, Issue 34 2010Magnus Rueping Abstract A bifunctional, cinchonidine-based, thiourea catalyst is shown to catalyze the enantioselective domino Michael,Henry reaction of cyclohexadienone (I) with various ,-nitrostyrenes. [source] Enantioselective Radical Reactions: Formation of Chiral Quaternary Centers.CHEMINFORM, Issue 30 2006Mukund P. Sibi 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] Oxonia-Cope Prins Cyclizations: A Facile Method for the Synthesis of Tetrahydropyranones Bearing Quaternary Centers.CHEMINFORM, Issue 17 2005Jackline E. Dalgard No abstract is available for this article. [source] Borane-Mediated Aldol Cycloreduction of Monoenone Monoketones: Diastereoselective Formation of Quaternary Centers.CHEMINFORM, Issue 21 2003Ryan R. Huddleston Abstract For Abstract see ChemInform Abstract in Full Text. [source] Copper-Catalyzed Asymmetric Conjugate Addition of Trialkylaluminium Reagents to Trisubstituted Enones: Construction of Chiral Quaternary CentersCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2007Magali Vuagnoux-d'Augustin Abstract Me3Al, Et3Al, and vinylalane species undergo enantioselective conjugate addition to a wide range of 2- or 3-substituted enones (cyclopent-2-enones, cyclohex-2-enones, 3-methyl cyclohept-2-enone) in the presence of catalytic amount of copper salt (copper thiophene carboxylate, [Cu(CH3CN)4]BF4 or [CuOTf]2,C6H6) and tropos-phosphoramidite-based ligand. Thus, chiral quaternary centers can be built, with up to 98,% ee after rigorous optimization of experimental conditions. It was shown that the main important parameter was the order of the introduction of the reagents. Then, the generated enantioenriched aluminium enolates and the chiral conjugate adducts were functionalized and used for subsequent reactions. [source] Indium-Promoted Acyloxyallylation Reaction of Azetidine-2,3-diones in Aqueous Media: A New Route to Densely Functionalized 3-Substituted 3-Hydroxy-,-lactams,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 26 2008Benito Alcaide Abstract Densely functionalized 3-substituted 3-hydroxy-,-lactams have been obtained by acyloxyallylation reaction of azetidine-2,3-diones with 3-bromopropenyl acetate or benzoate in aqueous media promoted by indium under Barbier conditions. Two new stereocenters were formed; the stereochemistry at the new C-3 quaternary center was fully controlled by placing a bulky chiral substituent at C-4. However, poor diastereoselectivities were observed in the new allylicstereocenter formed (up to 58,% de).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Highly Selective Preparation of a Chiral Quaternary Allyl Aryl Piperidinedione by Palladium-Catalyzed Asymmetric Allylation Under Solid,Liquid Phase-Transfer CatalysisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 36 2007Audrey Nowicki Abstract The combination of a chiral palladium catalyst and a solid,liquid phase-transfer catalyst provides an effective method for the chemo- and enantioselective preparation of the chiral quaternary center of an allyl aryl piperidinedione. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Enantioselective Synthesis of the Originally Proposed Usneoidone Structure: Evidence for a Structural RevisionEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2004Michèle Danet Abstract The enantioselective synthesis of the initially proposed structure of usneoidone has been completed according to a convergent strategy in which the key steps were an enantioselective Michael addition involving chiral imines to set up the C12 quaternary center, and the final assembly of the chiral pyran moiety with the aromatic subunit through a cyanohydrin anion alkylation step. The obtained product displays spectroscopic data that significantly differ from the reported values. A putative revised structure in which the pyran ring is opened is proposed for usneoidones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Phase-Transfer-Catalyzed Olefin Isomerization/,-Alkylation of ,-Alkynylcrotonates as a Route for 1,4-EnynesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Takuya Hashimoto Abstract The phase-transfer-catalyzed alkylation of ,-alkynylcrotonates was developed as a means to provide 1,4-enynes deconjugated by an all-carbon quaternary center. Extension to the asymmetric version using the chiral phase-transfer catalyst (S)- 3 provided the alkylated compounds with up to 87% ee. [source] Pyrrolidine-Camphor Derivative as an Organocatalyst for Asymmetic Michael Additions of ,,,-Disubstituted Aldehydes to ,-Nitroalkenes: Construction of Quaternary Carbon-Bearing Aldehydes under Solvent-Free ConditionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Chihliang Chang Abstract A novel pyrrolidine-camphor organocatalyst 3 was designed, synthesized and proven to be an efficient catalyst for the asymmetric Michael reaction. Treatment of ,,,-disubstituted aldehydes with ,-nitroalkenes in the presence of 20,mol% organocatalyst 3 and 20,mol% benzoic acid under solvent-free conditions provided the desired Michael product possessing an all-carbon quaternary center with high chemical yields (up to 99% yield) and high levels of enantioselectivities (up to 95% ee). [source] Exploring Chiral Space en route to DPC 963: A Personal AccountADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2003William Abstract DPC 961 and DPC 963 are non-nucleoside reverse transcriptase inhibitors (NNRTIs) for the treatment of HIV. These drug candidates contain a chiral quaternary center, which can be installed via addition of lithium cyclopropylacetylide to an N -acylketimine in the presence of a chiral moderator. This account describes our efforts to identify a cost-effective moderator by rapidly preparing, screening, and optimizing libraries of enantiopure ,-amino alcohols. The result is a highly enantioselective process that has been used to produce these NNRTIs on a metric ton scale. [source] In the Quest for a Virtual Pseudo Receptor for Sandalwood-Like Odorants.CHEMISTRY & BIODIVERSITY, Issue 7 2004Based on similarities between naturally occurring (,)-(Z)- , - or (+)-(Z)- , -santalol ((,)- 1 or (+)- 2, resp.) and the reversed (E)-configured synthetic derivatives from campholenal (7a), a simple model A was developed. Besides reconciliation of this stereochemical aspect, this initial model also tentatively explained the enantiodiscriminations as well as the large spectra of distances separating the OH function from the lipophilic quaternary center(s) reported for different classes of substrates. Evolution, modifications, and refinement of this imperfect model allied with the research for alternative possibilities are illustrated, along with a historical guideline, in the light of olfactively challenging synthetic seco-substructures as well as literature reports. Despite evolution of the inadequate model A and a plausible interpretation of the lipophilic part, the topological positions of the OH function and its vicinal alkyl substituent could nevertheless not be fully ascertained by this approach. This apparently inconclusive empirical concept prompted us to turn our attention towards a computerized methodology, which will constitute the second and third part of this study. [source] Enantioselective Synthesis of 4-(Dimethylamino)pyridines through a Chemical Oxidation-Enzymatic Reduction Sequence.ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2006Application in Asymmetric Catalysis Abstract Enantiomerically pure 4-(dimethylamino)-3-(1-hydroxyalkyl)pyridines and 4-(dimethylamino)-3-[hydroxy(phenyl)methyl]pyridine have been prepared through efficient chemoenzymatic routes. For this purpose different lipases and oxidoreductases have been tested in the preparation of optically active 4-chloro derivatives and baker's yeast was found to be an excellent catalyst for the bioreductions of the corresponding ketones. Their applications as enantioselective nucleophilic catalysts have been studied, important catalytic properties were observed in the stereoselective construction of quaternary centers. [source] High Diversity on Simple Substrates: 1,4-Dihalo-2-butenes and Other Difunctionalized Allylic Halides for Copper-Catalyzed SN2, ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2008Caroline A. Falciola Dr. Abstract Enantioselective allylic alkylation with an organomagnesium reagent catalyzed by copper thiophene carboxylate (CuTC) was carried out on difunctionalized substrates, such as commercially available 1,4-dichloro-2-butene and 1,4-dibromo-2-butene, and on similar compounds of higher substitution pattern of the olefin for the formation of all-carbon chiral quaternary centers. The high regioselectivity obtained throughout the reactions favored good regiocontrol for the addition of phenyl Grignard reagents. Other difunctionalized substrates (allylic ethers and allylic alcohols) also underwent asymmetric SN2, substitution. [source] Copper-Catalyzed Asymmetric Conjugate Addition of Trialkylaluminium Reagents to Trisubstituted Enones: Construction of Chiral Quaternary CentersCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2007Magali Vuagnoux-d'Augustin Abstract Me3Al, Et3Al, and vinylalane species undergo enantioselective conjugate addition to a wide range of 2- or 3-substituted enones (cyclopent-2-enones, cyclohex-2-enones, 3-methyl cyclohept-2-enone) in the presence of catalytic amount of copper salt (copper thiophene carboxylate, [Cu(CH3CN)4]BF4 or [CuOTf]2,C6H6) and tropos-phosphoramidite-based ligand. Thus, chiral quaternary centers can be built, with up to 98,% ee after rigorous optimization of experimental conditions. It was shown that the main important parameter was the order of the introduction of the reagents. Then, the generated enantioenriched aluminium enolates and the chiral conjugate adducts were functionalized and used for subsequent reactions. [source] | ||||||||||||||||||||||