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  • Asymmetric synthesis  (10)
  • Baeyer-Villiger reaction  (2)
  • Alkylations
  • 1995-1999  (12)
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Keywords
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Year
  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: SAMP/RAMP Hydrazones ; Asymmetric synthesis ; Michael addition ; 4-Oxophosphonates ; Michael Michael tandem addition ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507160
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Keywords: Phoracantholide I, enantioselective synthesis ; SAMP hydrazone ; Baeyer-Villiger reaction ; Defensive secretion, component of ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199506153
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Keywords: Amino alcohols ; Asymmetric synthesis ; Oxa Michael addition ; 1,3-Dipolar cycloaddition ; Nitrile oxides ; C-O bond cleavage ; Nitro alkenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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%).
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Keywords: Amino alcohols ; Asymmetric synthesis ; Oxa Michael addition ; Nitro alkenes ; C-O bond cleavage ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Keywords: Ferrocene ; Asymmetric synthesis ; Nucleophilic 1,2-addition ; Hydrazones ; Cleavage reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    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
    Keywords: Asymmetric synthesis ; Hydrazones ; Synthetic methods ; Alkylations ; Deoxygenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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%).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    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
    Keywords: (+)-Aspicilin ; Macrolide, asymmetric synthesis of ; SAMP/RAMP hydrazones, diastereoselective alkylation ; 2,2-Dimethyl-1,3-dioxan-5-one ; Baeyer-Villiger reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199507161
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  • 8
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis of Primary Amines by Nucleophilic Addition of Alkyllithium Compounds to Aldehyde SAMP/RAMP Hydrazones (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1089-1100 
    Details
    ISSN: 0947-3440
    Keywords: Asymmetric synthesis ; Primary amines ; Nucleophilic 1,2-addition ; N—N bond cleavage ; Hydrazones ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aldehydes 1 or 5 are converted to the SAMP hydrazones 2 or the α-alkylated SAMP hydrazones 7 and treated with organolithium compounds at low temperature. Cleavage of the N—N bond of the resulting hydrazines 3 and 8 with Raney-Ni/H2, or of the N-methoxycarbonylhydrazines 9 with Li/NH3, yield the amines 4 with 61-90% ee, the amines 11 with 45-96% de and 93 → 99% ee. The absolute configuration of the amines 11 was established by X-ray analysis of an appropriate MTPA derivative.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970608
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  • 9
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis of (R,S)-Dehydroiridodial, (R,S)-Dehydroiridodiol and AnaloguesDedicated to Professor Karl-Heinz Büchel on the occasion of his 65th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 485-493 
    Details
    ISSN: 0947-3440
    Keywords: Michael addition ; Asymmetric synthesis ; Hydrazones ; Dehydroiridodiol ; Dehydroiridodial ; Cyclopentanoid monoterpenes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of (R,S)-(-)-dehydroiridodiol(dial) [(R,S)-6b], isolated from the plant Actinidia polygama Miq., and its analogues, in high diastereo- and enantiomeric purity (ee ≥ 96%) is described. Key steps of the synthesis are the Michael addition of metallated SAMP hydrazones [(S)-1] to the 2-cyclopentenecarboxylate 2 and subsequent conversion to the 5-substituted 2-methylcyclopentenecarboxylates 5.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970308
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  • 10
    Electronic Resource
    Electronic Resource
    Diastereo- and Enantioselective Synthesis of Carbocyclic and Heterocyclic β-Amino Acids by Tandem Aza Michael Addition/Intramolecular CyclizationDedicated to Professor Peter Welzel on the occasion of his 60th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 699-706 
    Details
    ISSN: 0947-3440
    Keywords: β-Amino acids ; Michael addition ; Chiral ammonia equivalent ; TMS-SAMP ; MIRC reaction ; Asymmetric synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereoselective conjugate addition of (S)-(-)-1-(trimethylsilylamino)-2-(methoxymethyl)pyrrolidine (TMS-SAMP) to ω-halide-substituted α,β-unsaturated esters 1 is utilized to prepare carbocyclic and heterocyclic β-amino acids 2 and 5 of high diastereo- and enantiomeric purity via the corresponding β-hydrazino esters by selective intramolecular alkylation of the intermediate ester enolate or the hydrazino moiety. The auxiliary is removed by reductive N—N bond cleavage. The stereochemistry of the resulting trans-2-aminocycloalkanecarboxylic acids (2) and azacycloalk-2-ylacetic acid esters (5) is confirmed by NMR spectroscopy and polarimetry. A transition-state model for the highly diastereoselective conjugate addition of TMS-SAMP to enoates is presented.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970410
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