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  • 1990-1994  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    Stereochemistry of the Robinson Anellation: Studies on the Mode of Formation of the Intermediate Hydroxy Ketones (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1621-1636 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The stereochemical outcome of the base-catalyzed cyclization of diketones 5-8 has been investigated under protic conditions (Scheme 3). The more stable trans-fused ketols are preferentially formed in kinetically controlled aldol reactions, when the incipient angular substituent R = H (6 → 10a) or CN (7 → 11a, 8a → 12a). For R = Me (as in 5), axial attack of the side-chain enolate double bond on the ring C≡O group results in the rather selective formation of cis-9b. It is assumed that these cyclizations are controlled by relative product stabilities (product-like transition state) and steric effects. The competition between fused (e.g. 9) and bridged ketol (e.g. 13) formation in these cyclizations is discussed. The cis-fused (‘steroid’) ketols were readily equilibrated with their trans-counterparts (9b ⇄ 9a, 10b ⇄ 10a, 11b ⇄ 11a) under aprotic conditions (5 mol-% of LDA, THF, 0°), thus, allowing assessments of relative stabilities.
    Zusätzliches Material: 6 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19900730607
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    1,2,3,4,4a,5,8,8a-Octahydro-4β,8aα-dimethylnaphthalen-4aβ-ol ( = Dehydrogeosmin), a Novel Compound Occurring in the Flower Scent of Various Species of cactaceae (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 133-139 
    Details
    ISSN: 0018-019X
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The 1,2,3,4,4a,5,8,8a-octahydro-4β8aα-dimethylnaphthalen-4aβ-ol (= dehydrogeosmin; 1) has been identified as the olfactorily dominant compound in the flower scents of Rebutia marsoneri WERD., Dolichothele longimamma (DC.) BR. et R., and Sulcorebutia kruegeri (CARD.) RITT. The structure of 1, which might be of importance to the pollination biology of such Cactaceae, is based on spectral data and synthesis.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/hlca.19900730114
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