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  • 1980-1984  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Orthocarbonsäure-ester mit 2,4,10-Trioxaadamantanstruktur als Carboxylschutzgruppe; Verwendung zur Synthese von substituierten Carbonsäuren mit Hilfe von Grignard-Reagenzien (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 2294-2307 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ortho Esters with 2,4,10-Trioxaadamantane Structure as Carboxyl Protecting Group; Applications in the Synthesis of Substituted Carboxylic Acids by Means of Grignard ReagentsThe surprising stability of 2,4,10-trioxa-3-adamantyl derivatives 1 against nucleophilic substitution by organomagnesium compounds is discussed and shown to be caused by unfavourable stereoelectronic and steric factors governing the substitution of these cage compounds (Scheme 2). As a consequence, a number of Grignard reagents 2 containing the carboxyl group masked as 2,4,10-trioxa-3-adamantyl group could be prepared and have been reacted in a second step with various electrophiles (cf. Scheme 4). In the products 7-13 and 15b the carboxyl masking group is removed by mild acid hydrolysis and saponification (cf. Scheme 3) to yield the corresponding acids 16a-21a, 22, and 23a. Acids 21a and 23a have been further transformed to give the macrocyclic lactones 24 and 26, isolated from Galbanum oleo-gum-resin, and acid 22 to give 12-methyl-13-tridecanolide (25), isolated from Angelica root oil. In addition 1-bromo-ω-(2,4, 10-trioxa-3-adamantyl)alkanes 1c and 1b have been used to synthesize (±)-methyl recifeiolate (29b) and pure cis-ambrettolic acid ((Z)-32a).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660741
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  • 2
    Electronic Resource
    Electronic Resource
    Synthese des Dysidins (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1783-1792 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of DysidinThe synthesis of dysidin ((-)-1), the enantiomer of a metabolite of the marine sponge Dysidea herbacea, is described. To effect the synthesis, (±)-5-isopropyl-4-methoxy-3-pyrrolin-2-one (7) is converted to its lithium salt and reacted with (-)-(5R,2E)-3-methoxy-5-trichloromethyl-2-hexenoyl chloride ((-)-11) to give (-)-1 and its diastereoisomer (+)-5-epidysidin ((+)-12) epimeric at C(5) of the pyrrolinone ring. The (-)-acyl chloride (-)-11 has been synthesized from (+)-(R)-3-(trichloromethyl)butanoic acid ((+)-8) via the intermediates (+)-9 and (-)-10, the pyrrolinone 7 from N-benzyl-oxycarbonyl-L-valine via the intermediate 5. The enantiomers of acid 8 have been resolved by fractional crystallization of their diastereoisomeric N-(1-phenylethyl)amides. The (R)-chirality of (+)-8 was determined by comparing the 1H-NMR spectra of the diastereoisomeric N-(1-phenylethyl)amides 16 and 17, made from (+)-8 by substituting deuterium for chlorine, with the spectra of the N-(1-phenylethyl)amides 14 and 15 of known absolute configuration. This correlation shows that literature value (R) for (-)-8 is in error. Therefore, the structural formulae of (-)-dysidenin and (+)-isodysidenin, two other metabolites of D.herbacea, have to be changed to their mirror images as shown in formulae (-)-3 and (+)-4, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670716
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  • 3
    Electronic Resource
    Electronic Resource
    Synthese von (±)-Diplodialid B und A (1980)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 63 (1980), S. 2426-2433 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of (±)-Diplodialide B and ATwo steroid hydroxylase inhibitors, diplodialide B (1) and A (2) have been synthesized in the following way: The lithium enolate 5 of S-t-butyl thioacetate (4) was added to (E)-7-(2′-tetrahydropyranoxy)-2-octen-1-al (8) and the newly formed 3-hydroxy group in the product 9 was protected as t-butyl-diphenyl silyl ether followed by selective hydrolysis of the tetrahydropyranyl ether to give 10. Treatment with AgNO3/H2O cleaved the S-t-butyl ester group in 10 to give the corresponding hydroxy carboxylic acid which was converted into the S-2-pyridyl thioester by treatment with di(2-pyridyl)disulfide and triphenyl phosphine and cyclized with AgClO4 to give the (4E,3,9-trans)- and (4E,3,9-cis)-lactone 11 and 12 (R=t-Bu(C6H5)2Si) in 67% yield. Chromatographic separation of 11 and 12 and cleavage of the t-butyl-diphenyl silyl ether with tetrabutyl ammonium fluoride yielded (±)-diplodialide B (1) with (4E,3,9-trans)-configuration and the (4E,3,9-cis)-isomer 12 (R=H). Both isomers could be oxidized to diplodialide A (2) with manganese dioxide. The synthesis described above has also been carried out via the intermediates 10, 11 and 12 with R=COOCH2CH2Si(CH3)3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19800630835
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  • 4
    Electronic Resource
    Electronic Resource
    Synthese der Phoracantholide K, O und M (1980)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 63 (1980), S. 2312-2319 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Phoracantholide K, O and MTwo 14membered ring lactones 3 and 4 and a 12membered ring lactone 5 isolated from the metasternal secretion of the eucalypt longicorn Phoracantha synonyma have been synthesized as racemic mixtures by the following method. Reaction of the dilithium derivative of 5-hexynoic acid (6) with threo-8-bromo-2,4-isopropylidenedioxyoctane (7), followed by removal of the protecting group and esterification with diazomethane gave methyl-threo-11, 13-dihydroxy-5-tetradecy-noate (8) (s. Scheme 2). Partial hydrogenation of the triple bond in 8 with Lindlar Pd-catalyst, followed by saponification lead to (threo, Z)-11, 13-dihydroxy-5-tetra-decenoic acid (10). The dihydroxy acid 10 was converted into the S-(2-pyridyl) thioate and cyclized in diluted benzene solution under the influence of silver ions to yield the corresponding 12- and 14-membered lactones in approximately equal amounts. Isomerization of the mixture with p-toluenesulfonic acid in methylene chloride yielded the 14-membered lactone (cis-11, 13-5Z)-11-hydroxy-5-tetradecen-13-olide almost exclusively. It proved to be identical in its properties with natural phoracantholide K (3). With 5-hexynoic acid and 7-tetrahydropyranyloxy-octyl bromide or 5-tetrahydropyranyloxy-hexyl bromide as starting materials (±)-phoracantholide O (4) and M (5) have been synthesized in an analogous manner.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19800630821
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  • 5
    Electronic Resource
    Electronic Resource
    Synthese der enantiomeren Melochinine (1982)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1982 (1982), S. 1466-1477 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of the Enantiomeric MelochininesBoth enantiomers of the pyridone alkaloid melochinine (1) have been synthesized in the following way: The dienolate dianion 3a, formed exclusively from 3-hydroxy-2,6-dimethyl-4-pyrone (3) and lithium bis(trimethylsilyl)amide at - 70°C, reacts with 10-(tetrahydro-2-pyranyloxy)-1-undecanal (6) to give 7, then 8 by methylation, 9 by elimination of water, and finally the pyrone 10 by catalytic hydrogenation in 48% overall yield. Reaction of 10 with ammonia/methanol produces rac-1. Natural (-)-(R)-melochinine (1) and its artificial enantiomer are produced by using the aldehydes (R)-6 and (S)-6 in the synthesis described above. The enantiomeric aldehydes (R)-6 and (S)-6 are prepared in three steps from (+)-(R)- and (-)-(S)-1,2-epoxypropane, respectively. The starting material 3 ist produced from 1-(5-methyl-2-furyl)ethanol (2) by treatment with chlorine/water.
    Notes: Beide Enantiomeren des Pyridonalkaloids Melochinin (1) werden auf folgende Weise synthetisiert: Bei der Deprotonierung von 3-Hydroxy-2,6-dimethyl-4-pyron (3) mit Lithium-bis(trimethylsilyl)amid bei - 70°C entsteht ausschließlich das Dienolat-Dianion 3a. Es reagiert bei dieser Temperatur mit 10-(Tetrahydro-2-pyranyloxy)-1-undecanal (6) zur Verbindung 7, welche durch Methylieren, Eliminieren von Wasser und katalytisches Hydrieren über 8 und 9 mit 48% Gesamtausbeute in das Pyron 10 übergeführt wird. Einwirkung von Ammoniak/Methanol auf 10 ergibt rac-1. Das natürliche (-)-(R)-Melochinin (1) und sein in der Natur nicht vorkommendes Enantiomeres werden erhalten, wenn man in der Synthese die Aldehyde (R)-6 und (S)-6 einsetzt. Die enantiomeren Aldehyde 6 werden in drei Stufen aus (+)-(R)- bzw. (-)-(S)-1,2-Epoxypropan erhalten. Das Ausgangsmaterial 3 entsteht aus 1-(5-Methyl-2-furyl)ethanol (2) durch Reaktion mit Chlor/Wasser.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198219820806
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