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  • 1
    ISSN: 0947-3440
    Keywords: 3,7-Dioxa-2-azabicyclo[3.3.0]octanes ; 2,6-Dioxa-3-azatricyclo[5.3.1.04.11]undecanes ; Amino alcohols ; Chiral ligands ; Enantioselective catalysis ; Homogenous catalysis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reduction of the enantiomerically pure allyloxy esters 9 or ent-9 with DIBAH afforded the corresponding aldehydes which were treated in situ with chiral or achiral hydroxylamines 8 to give nitrones 10. These underwent a spontaneous intramolecular 1,3-dipolar cycloaddition, affording the bicyclic compounds 11 and 12, respectively. In an analogous manner, a mixture of the tricyclic compounds 14 and 15 was prepared. Treatment of compound 16 with cyclohexene oxide afforded a mixture of diastereomers 17 and 18. Diastereomers 14 and 15 as well as 17 and 18 could be separated by chromatography. X-ray analyses of compounds 11Ff, 17, and 11Af · HCl were performed. The bicyclic and tricyclic compounds were used as chiral ligands in the reaction of diethylzinc with aldehydes 19, in particular with benzaldehyde (19a). Using bicyclic compounds with a tertiary β-hydroxyalkyl substitutent at the N atom as ligands, ee's in the range of 78 to 95% were found. Whereas for the best ligands 11Ae and Af the enantioselectivity in the reaction of 4-tolualdehyde was only slightly decreased, with the aliphatic aldehydes 19c and d distinctly lower enantioselectivities were determined.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 469-471 
    ISSN: 0947-3440
    Keywords: Cycloadditions ; Asymmetric Synthesis ; Heterocycles ; Alkynes ; Reductions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral nonracemic compound 4 was prepared from ethyl (S)-(-)-lactate and 1,4-dibromo-2-butyne. Reduction with DIBAH at -72°C and subsequent treatment of the resulting dialdehyde with N-methylhydroxylamine yielded the dinitrone 5, which underwent two consecutive intramolecular cycloadditions to give the chiral nonracemic compound 7. The structure of 7 was confirmed by an X-ray analysis. Reductive ring opening afforded compound 8.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1649-1653 
    ISSN: 0947-3440
    Keywords: 9-Oxa-3-thia-10-azatricyclo[6.2.1.04,10]undecanes, 6-heteroatom-substituted ; 3-Thiazoline N-oxides ; Mercaptoacetaldehyde ; 1,3-Dipolar cycloadditions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5-Alkenal oximes 4, 12, and 13 were prepared by various methods. These oximes undergo a domino reaction with mercaptoacetaldehyde (1-M) affording tricyclic compounds 6, 17 and 18, respectively. At first the mercapto group adds to the oxime function forming a hydroxyamino moiety which then condenses with the aldehyde group giving the cyclic nitrones 10, 15, and 16, resp., as intermediates. These nitrones undergo spontaneously an intramolecular cycloaddition yielding the tricyclic compounds (6, 17, 18). The regioselectivity of the latter reaction step is opposite to that observed for corresponding intermolecular nitrone cycloadditions. The domino reaction proceeds highly selectively affording only one of the diastereomers. Starting from enantiomerically pure oxime 13, we prepared optically active 18. The stereogenic center of 13 induces the formation of three further stereogenic centers in the product. The configuration at C-5 of 18 was determined by a NOESY experiment.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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