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  • 1
    Electronic Resource
    Electronic Resource
    Stereochemie von Metallocenen, 42. Mitt.: Optisch aktives π-Fluorenon-tricarbonylchrom — Darstellung, enantiomere REinheit, absolute Konfiguration und Versuche zur Racemisierung (1978)
    Springer
    Monatshefte für Chemie 109 (1978), S. 1227-1240 
    Details
    ISSN: 1434-4475
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Racemic Fluorenone-Cr(CO)3 (1) was prepared from fluorenone ethyleneketal by complexation with Cr(CO)6 and subsequent cleavage of the dioxolane9. Asymmetric reduction of1 with a chiral Lithium hydride afforded both (+)-1 and the correspondingendo-carbinol (−)-7 a with optical yields up to 80% as established by the use of chiral nmr shiftreagents. Active1 could also be obtained by two other asymmetric reactions albeit with low optical yields. LiAlH4−AlCl3 reduction of (+)-1 gave traces of (+)-fluorene-Cr(CO)3 (2). The absolute chirality of (+)-1 was deduced as (S) by application of the abovementioned asymmetric reduction to ferroceno indenone (11) of known configuration and byHoreau's method to (−)-7 a. Several attempts to racemize1 failed, which proves that no transanular shift of Cr(CO)3 takes place. The CD spectra of1 and2 are reported. Some side reactions such as the reduction of7 a to2 with Cr(CO)6 in dibutylether (leading also to the formation of isomeric dimethylbenchrotrenes from the solvent) and the formation of a binuclear complex14 between1 and2 are briefly reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00913024
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  • 2
    Electronic Resource
    Electronic Resource
    Stereochemie von Metallocenen, 43. Mitt.: Torsionsisomere Biphenyl-tricarbonylchrom-Komplexe: Darstellung, Konformationsanalyse und Kinetik der Interkonversion (1979)
    Springer
    Monatshefte für Chemie 110 (1979), S. 437-451 
    Details
    ISSN: 1434-4475
    Keywords: Conformational analysis ; Lanthanide induced shift ; NMR, coalescence ; Optical activity ; Rotational barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Complexation of methyl 3-nitro-2-(o-tolyl)-benzoate (2, ano-trisubstituted biphenyl) with hexacarbonyl chromium gave the isomeric Cr(CO)3 complexes3 and4 both existing as two torsional isomersa andb, as seen by nmr. For the main product3 the preferred conformations of the two torsional isomersa andb were deduced by the lanthanide induced shift (LIS) technique. The activation energy for the interconversion process could be determined from kinetic measurements and especially from1H-nmr coalescence temperature of the methylsignals. The barrier of 91±1.5 kJ/mol (21.7±0.3 kcal/mol) in3 reflects the interaction of theo-H-atom of the benzene ring passing the Cr(CO)3 moiety of the benchrotrene ring during the interconversion. A partial optical resolution of3 was achieved by asymmetric reduction with a chiral lithium-aluminium hydride yielding (+)-3 with [α] D 20 +30° (benzene) and the levorotatory alcohol (−)-7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00911932
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Bildung von Xylol-tricarbonylchrom (Dimethylbenchrotrenen) aus Di-n-butylether und Hexacarbonylchrom (1979)
    Springer
    Monatshefte für Chemie 110 (1979), S. 1067-1075 
    Details
    ISSN: 1434-4475
    Keywords: Di-n-butylether ; 4,4′-dideuterated ; Di-n-pentylether ; Isobutylbenchrotrene ; Methyl-propyl-benchrotrene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The reaction of fluorenone ethyleneketal (9), diphenic anhydride as well as of biphenyls such as4 with Cr(CO)6 in refluxing di-n-butylether (BE) gives dimethylbenchrotrenes [xylene-Cr(CO)3,7] which are also formed by refluxing pureBE with Cr(CO)6—although with much lower yields. Similarily, from di-n-pentylether and Cr(CO)6 isobutyl- and 1-methyl-3-propyl-benchrotrene (13 and14) were obtained, whilst from di-n-propyl- and-hexylether, resp., and Cr(CO)6 no benchrotrenes could be isolated. Tentative assumptions on the “catalytic” action of certain functional groups were confirmed by the reaction ofBE and Cr(CO)6 in the presence of carbonamides, such as acetamide, urea and pyrrolidone, where 1,4-dimethylbenchrotrene (7 c) was formed with appreciable yields. Studies using dideuteratedBE showed that—at least for the reaction of9 with Cr(CO)6 (giving a much lower yield of7 than with undeuteratedBE)—a simple bimolecular mechanism can be excluded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00910954
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  • 4
    Electronic Resource
    Electronic Resource
    Stereochemie von Metallocenen, 44. Mitt.: Darstellung und Konfiguration von Tricarbonylchrom-Komplexen der Diphensäure und ihrer Derivate 3. Mitt. über Biphenyl-tricarbonylchrom-Komplexe (1980)
    Springer
    Monatshefte für Chemie 111 (1980), S. 259-274 
    Details
    ISSN: 1434-4475
    Keywords: Benchrotrenes ; Hydrogen bridges, intramolecular ; Lactone of 2′-hydroxymethyl-biphenyl-2-carboxylic acid, mono and bis tricarbonylchromium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Mono and bis tricarbonylchromium complexes of diphenic acid and its monomethylester (3, 4, 15, 16) were prepared by treating the corresponding methyl and trimethylsilylesters (e.g.12) with Cr(CO)6 and subsequent hydrolysis of the complexes1, 2, 13, and14. Diborane reduction of the carboxylic acids gave hydroxymethyl derivatives, amongst which the diol8 a is a key substance for configurational analyses by1H-nmr and ir spectroscopy. In this context monosubstituted biphenyl complexes (9–11) were prepared as reference substances. Complexation of the lactone23 of 2′-hydroxymethyl biphenyl-2-carboxylic acid afforded (besides two isomeric monocomplexes) mainly thetrans-biscomplex26 b, a key intermediate for ring opening and cyclization reactions. The stereochemical possibilities of the biscomplexes are discussed. The “racemate” configuration is preliminarily assigned to diphenic acid bistricarbonylchromium and its derivatives.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00938733
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  • 5
    Electronic Resource
    Electronic Resource
    Biphenyl(tricarbonylchrom)-Komplexe, V. Optisch aktive Tricarbonylchrom-Komplexe der Diphensäure und ihrer Derivate  -  Enantiomerenreinheit, Circulardichroismus und absolute Konfiguration (1980)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1980 (1980), S. 1877-1888 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Stereochemistry of Metallocenes, XLVI1).  -  Biphenyl(tricarbonylchromium) Complexes, V1).  -  Optically Active Tricarbonylchromium Complexes of Diphenic Acid and its Derivatives  -  Enantiomeric Purity, Circular Dichroism and Absolute ConfigurationOptically active mono and bis(tricarbonylchromium) complexes of diphenic acid and its monomethyl ester (cf. 7 and 8) were prepared by resolution via their cinchonidinium salts with enantiomeric purities up to 8%. Kinetic resolution of the corresponding aldehyde 12 via reduction with a chiral lithium aluminium hydride was more successful. In this case either ( + )-12 and the alcohol (-)-10 or the lactone (-)-16 were obtained. The maximum rotations [α]20D (in acetone) were determined by application of a chiral shift reagent to (-)-10 being 516°, 832° and 1094° for 10, 12 and 16; the optical yield of the asymmetric reduction was 33%. Because of the preferred configurations and conformations of the biscomplexes and after comparing the CD spectra with those of benchrotrenes of known absolute configuration the chirality (5)M-(R)A-(S)M is proposed for (-)-10 and related biphenyl complexes (-)-12 and (-)-16.
    Notes: Optisch aktive Mono- und Bis(tricarbonylchrom)-Komplexe der Diphensäure und ihres Monomethylesters (vergleiche 7 und 8) wurden durch Racematspaltung über die Cinchonidiniumsalze mit enantiomeren Reinheiten bis zu 8% erhalten. Bessere Ergebnisse lieferte die kinetische Racematspaltung durch Reduktion des entsprechenden Aldehyds 12 mit einem chiralen Lithiumaluminiumhydrid, wobei entweder ( + )-12 und der Alkohol (-)-10 oder das Lacton (-)-16 entstanden. Die maximalen [α]20D-Werte (in Aceton) wurden durch Anwendung eines chiralen Verschiebungsreagenzes auf (-)-10 ermittelt. Sie betragen für 10, 12 und 16 516°, 832° und 1094°. Für die optische Ausbeute der asymmetrischen Reduktion wurde 33% ermittelt. Aufgrund der bevorzugten Konfiguration und Konformation der Bis-Komplexe wird nach Vergleich der CD-Spektren mit jenen von Benchrotrenen bekannter Absolutkonfiguration für (-)-10 und die damit korrelierten Biphenylkomplexe (-)-12 und (-)-16 die Chiralität (5)M-(R)A-(S)M vorgeschlagen.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198019801124
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