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  • Asymmetric synthesis  (13)
  • Baeyer-Villiger reaction  (3)
  • Alkylations  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    Enantioselective Synthesis of Polyfunctional Small Building Blocks with a Quaternary Stereogenic Center (1994)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 127 (1994), S. 1707-1721 
    Details
    ISSN: 0009-2940
    Schlagwort(e): Asymmetric synthesis ; SAMP,RAMP-Hydrazones ; Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Application of the SAMP-/RAMP-hydrazone method offers an efficient and flexible access to compounds with a quaternary stereogenic center. Examples bearing silyl, thio, phenyl, aldo, keto, ester, and alkyl functionalities are described. The 2-phenylaldehydes and -ketones and the β-keto esters 4 were obtained in good overall yields and with variable enantiomeric excesses. The synthesis of the thiolated 2-formyl and 3-formyl carboxylic esters 12 was achieved in high overall yields and with high enantiomeric excesses. The silylated carboxylic ester and acids 16 were produced in moderate to high overall yields and with moderate to excellent enantiomeric excesses, depending on the electrophile used for the quaternization. The absolute configurations of the compounds 12 and 16 were determined by X-ray structure analyses, and the mechanism of the quaternization is postulated.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/cber.19941270922
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  • 2
    Digitale Medien
    Digitale Medien
    Asymmetric michael additions via SAMP/RAMP hydrazones enantioselective synthesis of 2-substituted 4-oxophosphonates (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1177-1184 
    Details
    ISSN: 0947-3440
    Schlagwort(e): SAMP/RAMP Hydrazones ; Asymmetric synthesis ; Michael addition ; 4-Oxophosphonates ; Michael Michael tandem addition ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Asymmetric Michael addition of lithiated methyl ketone SAMP hydrazones (S)-3 to a variety of alkenylphosphonates (E)-2 followed by oxidative cleavage of the 1,4-adducts (S,S)-4 by ozonolysis afforded 2-substituted 4-oxophosphonates (S)-5 in usually moderate to very good overall yields (14-77%) and with mostly high enantiomeric excesses (ee = 20-〉95%). In addition, asymmetric Michael Michael tandem additions were carried out in good overall yields by trapping the intermediate lithio phosphonate anions with alkenylphosphonate or enoate Michael acceptors.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.1995199507160
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  • 3
    Digitale Medien
    Digitale Medien
    A convenient enantioselective synthesis of (R)-(-)-phoracantholide I, a component of the defensive secretion of the eucalypt longicorn Phoracantha synonyma (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1127-1128 
    Details
    ISSN: 0947-3440
    Schlagwort(e): Phoracantholide I, enantioselective synthesis ; SAMP hydrazone ; Baeyer-Villiger reaction ; Defensive secretion, component of ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A short enantioselective synthesis of phoracantholide I [(R)-4] (ee = 91 %), a component of the defensive secretion of the eucalypt longicorn Phoracantha synonyma, is described. Key steps of the synthesis are the enantioselective α-alkylation of cyclononanone SAMP hydrazone [(S)-1] (de 〉 93%) and subsequent Baeyer-Villiger reaction of the ketone (R)-3 with retention of configuration.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.1995199506153
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  • 4
    Digitale Medien
    Digitale Medien
    Asymmetric Synthesis of α-Substituted β-Amino Sulfones by Aza-Michael Addition to Alkenyl Sulfones and Subsequent α-Alkylation (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 879-892 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Addition reactions ; Sulfones ; Alkylations ; Amines ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The aza-Michael addition of enantiopure 1-aminopyrrolidines to (E)-alkenyl sulfones in the presence of a catalytic amount of ytterbium trifluoromethanesulfonate [Yb(OTf)3] yields β-hydrazino sulfones in moderate to good yields and with diastereoselectivities of up to ≥ 98%. The latter undergo reductive N-N bond cleavage with BH3 · THF and, after N-protection with Boc2O or benzyl bromide, afford N-protected β-amino sulfones with moderate to high enantiomeric excesses (ee = 42 to ≥96%) without racemization. Subsequent α-alkylation of the N,N-dibenzyl protected β-amino sulfones with various electrophiles yields α-alkyl-β-amino sulfones in excellent yields (88-97%) with high diastereomeric (de ≥96 to ≥98%) and enantiomeric purity (ee = 94 to ≥96%). The absolute configuration of the new stereogenic centre was determined by X-ray structural analysis and confirmed by NMR spectroscopy (NOE experiments). Possible reaction mechanisms for the conjugate addition and α-alkylation are presented.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Formaldehyde SAMP-Hydrazone as a Neutral Formyl Anion Equivalent: Asymmetric Synthesis of Substituted β-Formyl δ-Lactones and Furofuran Lactones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 893-901 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Nucleophilic formylation ; Addition reactions ; Lactones ; Formyl anion equivalent ; Domino reactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---An efficient asymmetric synthesis of α-substituted β-formyl δ-lactones 5 (de ≥ 98%, ee = 80-95%) and 4-substituted furofuran lactones 6 (de ≥ 98%, ee = 80-〉98%) in acceptable overall yields is reported. Key steps of the new procedure are an asymmetric Michael addition of formaldehyde SAMP-hydrazone (1) to 5,6-dihydro-2H-pyran-2-one (2) under neutral conditions, followed by trans-selective α-alkylation and subsequent cleavage of the auxiliary by ozonolysis or a hydrolytic domino reaction protocol, respectively. The absolute configurations given for the title compounds are based on three X-ray structure analyses and NOE measurements.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Diastereo- and Enantioselective Synthesis of N-Protected 2-Amino 1,4-Diols by an Oxa Michael Addition/1,3-Dipolar Cycloaddition Protocol (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1793-1802 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Amino alcohols ; Asymmetric synthesis ; Oxa Michael addition ; 1,3-Dipolar cycloaddition ; Nitrile oxides ; C-O bond cleavage ; Nitro alkenes ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An enantioselective synthesis of N-protected amino diols has been accomplished by employing a diastereoselective inter- and intramolecular 1,3-dipolar cycloaddition reaction of optically active nitrile oxides as a key step. The nitro alkane starting materials were obtained by diastereoselective oxa Michael addition of (1R,2S)-(-)-N-formylnorephedrine (1) to aliphatic (E)-nitro alkenes 2, 6a, b (de = 96 - ≥ 98%). Subsequent diastereo- and regioselective cycloaddition reactions to highly substituted 4,5-isoxazolines 5a-e, 8a, b (52-81%) and reductive ring opening led - after cleavage of the auxiliary - to amino diols 13, 14 in good overall yields (27-40%, over five steps) and with excellent diastereomeric and enantiomeric excesses (de,ee ≥ 96%).
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Diastereo- and Enantioselective Synthesis of Vicinal Amino Alcohols by Oxa Michael Addition of N-Formylnorephedrine to Nitro Alkenes (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1771-1792 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Amino alcohols ; Asymmetric synthesis ; Oxa Michael addition ; Nitro alkenes ; C-O bond cleavage ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The first intermolecular asymmetric oxa Michael additions with removable chirality information within the hydroxide source are reported. As enantiopure oxygen nucleophile functioning as chiral hydroxide equivalent N-formylnorephedrine (7) was used and conjugate additions to aliphatic (E)-nitro alkenes 2a-j were carried out in good yields (35-87%) and excellent diastereomeric excesses (de = 94-≥98%). After reduction of the nitro group and protection of the amino function (11a-h, 73-87%, both steps), the cleavage of the auxiliary occurred without epimerisation (69-99%) using Na/NH3. The Boc-protected 2-amino alcohols 12a-h could be obtained in good overall yields (30-58 %, four steps) and excellent diastereomeric and enantiomeric excesses (de, ee = 94-≥98%). Transition states explaining the overall stereochemical outcome are presented based on the absolute configuration determined by X-ray structure analysis on 8b.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Asymmetric Synthesis of (1-Ferrocenylalkyl)amine and 1,1′-Bis(1-aminoalkyl)ferrocene Derivatives (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 689-696 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Ferrocene ; Asymmetric synthesis ; Nucleophilic 1,2-addition ; Hydrazones ; Cleavage reactions ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The aldehydes 1 and 5 were converted to the corresponding SAMP hydrazones 2 and 6, respectively. Subsequent nucleophilic 1,2-addition of organolithium reagents to the C-N double bonds and cleavage of the N-N hydrazine bond using an excess of BH3·THF afforded (1-ferrocenylalkyl)amines (N-protection → 4) and 1,1′-bis(1-aminoalkyl)ferrocenes (N-protection → 8) in good overall yields (32-88%), with very high enantiomeric excesses (ee = 90-98%) and dl/meso ratios of up to 95:5.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Highly Diastereo- and Enantioselective Synthesis of Protected anti-1,3-Diols (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2839-2849 
    Details
    ISSN: 1434-193X
    Schlagwort(e): Asymmetric synthesis ; Hydrazones ; Synthetic methods ; Alkylations ; Deoxygenation ; Chemistry ; General Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: An efficient asymmetric synthesis of protected anti-1,3-diols 5 (de ≥ 98%, ee = 92-98%) from 2,2-dimethyl-1,3-dioxan-5-one SAMP hydrazone 1 is described. The key steps are the diastereo- and enantioselective α,α′-bisalkylation followed by reduction of the ketones 2 and a variant of the Barton-McCombie deoxygenation. The new method allows the synthesis of acetonide-protected anti-1,3-diols with a broad range of substituents in good overall yields (31-69%).
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    Diastereo- and enantioselective synthesis of the 18-membered lichen macrolide (+)-aspicilinDedicated to Professor Hans-Dieter Scharf on the occasion of his 65th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1185-1191 
    Details
    ISSN: 0947-3440
    Schlagwort(e): (+)-Aspicilin ; Macrolide, asymmetric synthesis of ; SAMP/RAMP hydrazones, diastereoselective alkylation ; 2,2-Dimethyl-1,3-dioxan-5-one ; Baeyer-Villiger reaction ; Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The asymmetric synthesis of the lichen macrolide (+)-aspicilin (1) was realised in 19 steps and with high stereoselectivity (de ≥ 91 %, ee ≥ 96%). Three of the four stereogenic centres were generated by employing the SAMP/RAMP hydrazone method. Key steps of the synthesis are the α,α′-double alkylation of RAMP hydrazone (R)-10 of 2,2-dimethyl-1,3-dioxan-5-one B and the enantioselective synthesis of the bromo alcohol (S)-9 (subunit A) by a combination of SAMP hydrazone α-alkylation with subsequent Baeyer-Villiger oxidation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jlac.1995199507161
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