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  • Asymmetric synthesis  (13)
  • Baeyer-Villiger reaction  (3)
  • Alkylations  (2)
  • 1
    Electronic Resource
    Electronic Resource
    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
    Keywords: Asymmetric synthesis ; Nucleophilic formylation ; Addition reactions ; Lactones ; Formyl anion equivalent ; Domino reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---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.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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%).
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  • 3
    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.
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  • 4
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis of (+)- and (-)-Streptenol A (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 751-756 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Streptenol A ; Synthetic methods ; Natural products ; SAMP/RAMP hydrazones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The asymmetric synthesis of (+)-streptenol A was carried out in ten steps and with high enantioselectivity (ee ≥ 96%). The key steps are the α-alkylation of 2,2-dimethyl-1,3-dioxan-5-one RAMP hydrazone A (1), subsequent deoxygenation and elaboration of the side chain via aldehyde B to furnish (+)-streptenol A in 23% overall yield. In analogy, the enantiomer (-)-streptenol A was synthesized using the corresponding SAMP hydrazone in 18% overall yield.
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  • 5
    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.
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  • 6
    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.
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  • 7
    Electronic Resource
    Electronic Resource
    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
    Keywords: Asymmetric synthesis ; Addition reactions ; Sulfones ; Alkylations ; Amines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---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.
    Additional Material: 5 Ill.
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Enantioselective synthesis of α-phosphanyl ketones and 2-phosphanyl alcoholsDedicated to Professor Hans Paulsen on the occasion of his 75th birthday. (1997)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 345-363 
    Details
    ISSN: 0947-3440
    Keywords: α-Phosphanyl ketones ; 2-Phosphanyl alcohols ; α-Phosphanyl hydrazones ; Asymmetric α-phosphanylation ; Phosphane-borane adducts ; Asymmetric synthesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient, highly enantioselective methodology for the synthesis of α-phosphanyl ketones 7 and 2-phosphanyl alcohols 12 and 13, important hemilable ligands for enantioselective homogeneous catalysis and chiral building blocks in general, has been developed. The key step of this first enantio-selective synthesis of α-phosphanyl ketones is the diastereo-selective phosphanylation of SAMP hydrazones 2 to produce α-phosphanyl hydrazones, isolated as the more stable borane adducts 6. Subsequent ozonolysis afforded α-phosphanyl ketones 7. The enantioselective synthesis of 2-phosphanyl alcohols 12 and 13 has been accomplished by two fundamentally different procedures: the phosphanylation of unsubstituted chiral aldehyde hydrazones 9 and the alkylation of α-diphenylphopshanyl acetaldehyde SAMP hydrazone 10. After separation of the minor diastereomer, the borane-protected α-phosphanyl aldehyde hydrazones 11 were converted to unprotected 2-phosphanyl alcohols 13 by ozonolysis, reduction and removal of the borane group. The absolute configuration of the functionalized phosphanes was determined by X-ray analysis, NOE experiments or polarimetry.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199719970212
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  • 10
    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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