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  • Organic Chemistry  (25)
  • 1975-1979  (25)
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  • 1
    Electronic Resource
    Electronic Resource
    Zur Umpolung der Carbonylreaktivität; Deprotonierung von Ketenthioacetalen zu 1,1-dithiosubstituierten Allyl- und Pentadienyllithiumverbindungen sowie deren Reaktionen mit Elektrophilen (1977)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1977 (1977), S. 811-829 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactivity Umpolung of Carbonyl Compounds; Proton Abstraction from Ketene Thioacetals to Give 1,1-Dithio-substituted Allyl-and Pentadienyl-lithium Derivatives and Their Reactions with ElectrophilesThe terms Hn-abstraction as well as En- and Nn-attack at carbonyl derivatives are defined. Typically, carbonyl compounds normally undergo H2,4…-abstraction, E2,4…-and N1,3-…-attack (scheme 1). Carbonyl derivatives of type A in scheme 2 show an umpolung of these reactivities. Here, this is demonstrated by H3- (with butyllithium or lithium diisopropylamide in THF/hexamethylphosphoric triamide, 1 → 2) and H5-abstractions (5 → 6) from ketene thioacetals and alkylations of the organolithium derivatives formed to give 7 and 9, respectively (E1-attack). Hydrolysis to the α,β-unsaturated ketones 14 is the last step of two synthetically useful overall transformations shown in scheme 3.
    Notes: Die Begriffe Hn-Abstraktion, sowie En- und Nn-Angriff an Carbonylderivaten werden definiert. Bei Carbonylverbindungen sind normalerweise H2,4…-Abstraktion, E2,4…- und N1,3…-Angriff typisch (Schema 1). Carbonylderivate vom Typ A (Schema 2) zeigen dagegen eine Reaktivitätsumpolung. Dies wird hier an den Beispielen der H3-Abstraktion (durch Butyllithium oder Lithiumdiisopropylamid in THF mit Hexamethylphosphorsäuretriamid, 1 → 2) und H5-Abstraktion (5 → 6) aus Ketenthioacetalen mit anschließenden Alkylierungen der erhaltenen Lithiumorganyle zu den Produkten 7 und 9 unter E1-Angriff demonstriert. Hydrolyse zu den α, β-ungesättigten Ketonen 14 ist der letzte Schritt der in Schema 3 angegebenen synthetisch nützlichen Reaktionsfolge.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197719770512
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  • 2
    Electronic Resource
    Electronic Resource
    Synthese und Bestimmung der absoluten Konfiguration von Norpyrenophorin, Pyrenophorin und Vermiculin (1978)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1978 (1978), S. 2044-2073 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Syntheses and Determinations of the Absolute Configurations of Norpyrenophorin, Pyrenophorin, and Vermiculine1,2)The hydroxy acids 8, 10b, and 15b (see general formula E) with 1,3-dithiane-protected keto groups are synthesized in a few steps from the haloalkanes 4, 5, and 6, respectively. The chiral acids 10b and 15b are obtained in optically pure form if the starting materials 5 and 6, respectively, are synthesized from 3-hydroxybutyric acid and malic acid. Of the three most frequently used methods of macrocyclization (dipyridyl disulfide/triphenylphosphine, diethyl azodicarboxylate/triphenylphosphine, and 2-halopyridinium salt), only Mitsunobu's reaction with diethyl azodicarboxylate/triphenylphosphine works with the sulfur-containing hydroxy acids. The thioketal groups in the resulting diolides 16-18 are hydrolyzed with mercuric oxide/boron trifluoride to give the macrolides 1-3, pyrenophorin (2) and vermiculine (3) in a single enantiomeric form. Model studies outlined in equations (1) - (3) show that dimerizing esterification with diethyl azodicarboxylate/triphenylphosphine takes place with inversion at the center of chirality. Thus, the present syntheses of pyrenophorin (R,R-2) and vermiculine (S,S-3), see flowsheet in Scheme 1, also consitute assignments of the hitherto unknown absolute configurations of these natural products. The overall yields of reactions 4→1, 5→2, and 6→3 are 17, 27, and 8%.  -  A study of the antimicrobial activity shows no difference between (+)- and (-)-vermiculine or (-)-and (±)-pyrenophorin; the physiological activity of the unsubstituted, achiral diolide norpyrenophorin is essentially the same as that of pyrenophorin.
    Notes: Aus den Alkylhalogeniden 4, 5 und 6 werden in wenigen Schritten die Hydroxysäuren 8, 10b bzw. 15b (allgemeine Formel E) mit 1,3-Dithian-geschützten Ketogruppen synthetisiert. 10b und 15b erhält man in enantiomerenreiner Form, wenn man von den aus Hydroxybuttersäure oder Äpfelsäure leicht erhältlichen chiralen Vorläufern 5 bzw. 6 ausgeht. Von den drei gebräuchlichen Methoden der Makrocyclisierung (Dipyridyldisulfid/Triphenylphosphin, Azodicarbonsäure-diethyl-ester/Triphenylphosphin und 2-Halogenpyridiniumsalz) überführt nur die Reaktion mit Azodicarbonsäurediester/Triphenylphosphin nach Mitsunobu die schwefelhaltigen Hydroxysäuren in die Diolide 16-18, deren Thioacetalgruppen mit Quecksilber(II)-oxid/Bortrifluorid hydrolytisch abgespalten werden. Dabei entstehen die im Titel genannten Makrolide 1-3, Pyrenophorin (2) und Vermiculin (3) in optisch aktiver Form. Es wird durch Modellversuche [Gleichungen (1) - (3)] gezeigt, daß bei der dimerisierenden Veresterung mit Azodicarbonsäurediester/Triphenylphosphin Konfigurationsumkehr am alkoholischen Chiralitätszentrum eintritt. Dadurch sind die in Schema 1 zusammengefaßten Synthesen von Pyrenophorin (R,R-2) und Vermiculin (S,S-3) Bestimmungen der bisher unbekannten absoluten Konfigurationen dieser Naturstoffe. Die Gesamtausbeuten vom Alkylierungsmittel bis zu den Dioliden (4→1, 5→2 und 6→3) liegen bei 17, 27 bzw. 8%.  -  Eine Untersuchung des antimikrobiellen Wirkungsspektrums zeigt keinen Unterschied zwischen (+)- und (-)-Vermiculin oder (-)- und (±)-Pyrenophorin; die physiologische Wirksamkeit des am Diolidring unsubstituierten, achiralen Norpyrenophorins ist annähernd gleich der des Pyrenophorins.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197819781220
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Umpolung der Carbonylreaktivität; N2/E1- und N4/E1-Reaktion von 1,1-diheterosubstituierten Olefinen und Dienen (1977)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1977 (1977), S. 830-845 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Reactivity Umpolung of Carbonyl Compounds; N2/E1 and N4/E1-Reactions of 1,1-Dihetero-substituted Olefins and DienesAlkyllithium compounds (except CH3Li) add to olefins 1, 5, 10, and to the dienes 17. Substituted methyl 1-methylthiovinyl sulfoxides 12 combine similarly with lithium enolates. The carbanionoids formed are reacted with electrophiles (H⊕, D⊖, RX, R2CO) to give vinyl-silanes 3, vinylthio enol ethers 6, thioacetals 8, 19, and γ-methylsulfinyl γ-(methylthio) ketones 13, 14, respectively. These are converted into the carbonyl derivatives 4, 7, 9, 15, 16, and 20, respectively. The precursor olefins and dienes thus react equivalently to acyl anions, enolate cations, and vinylogous electrophilic „enolates“. [See A, B, C and equations (2) and (3).]
    Notes: Alkyllithiumverbindungen (außer CH3Li) addieren sich an die Olefine 1, 5, 10 und an die Diene 17. Die substituierten Methyl(1-methylthiovinyl)sulfoxide 12 reagieren ähnlich auch mit Lithiumenolaten. Die entstehenden Carbanionoide werden mit Elektrophilen (H⊕, D⊖, RX, R2CO) als Vinylsilane 3, Vinylthioenolether 6, 1,3-Dithiane 8, 19 und γ-Methylsulfinyl-γ-(methylthio)ketone 13 und -carbonsäureamide 14 abgefangen, die in die Carbonylderivate 4, 7, 9, 15, 16 bzw. 20 übergeführt werden. Die eingesetzten Olefine und Diene reagieren damit als Acylaninonen, Enolatkationen und vinyloge elektrophile „Enolate“. [Siehe A, B, C, sowie Gleichungen (2) und (3)].
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197719770513
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  • 4
    Electronic Resource
    Electronic Resource
    Erzeugung und Reaktionen des chiralen Lithiumenolats von (+)-(S)-3-Methyl-2-pentanon1,2) (1976)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1976 (1976), S. 1357-1369 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Generation and Reactions of the Chiral Lithium Enolate of +)-(S)-3-Methyl-2-pentanone(-+)-(S)-3-Methyl-2-pentanone (1) was synthesized from the readily available compounds 4-7 of known absolute configuration and optical purity. One route used nucleophilic acylations with 1,3-dithian-2-ylanion converting 5 to 8 and 9 with more than 90% inversion of configuration. Large amounts of 1 were prepared by reaction of the acid 10a with methyl- lithium. Lithium diisopropylamide generates the enolate 2 from 1 with less than 10% racemization. Electrophiles (alkyl iodides, acyl chlorides, aldehydes, ketones) combine with 2 to give the optically active ketones 12, 13, 15, and 16. For the aldol addition leading to 15b we showed that the newly formed asymmetric center has (R)-configuration (1 5 % induction).
    Notes: (+)-(S)-3-Methyl-2-pentanon (1) wurde aus den leicht zugänglichen Verbindungen 4-7 bekannter absoluter Konfiguration und optischer Reinheit über die Dithiane 8 und 9 hergestellt. Dabei wurde bewiesen, daß die nucleophile Substitution von Bromid durch die 1,3- Dithian-2-ylanionen zu über 90% unter Inversion abläuft. Größere Mengen 1 stellten wir aus der α-Methylbuttersäure 10a und Methyllithium her. Lithiumdiisopropylamid überführt 1 in das Enolat 2, wobei maximal 10 % Racemisierung eintritt. Mit Elektrophilen (Alkyljodide, Carbonsäurechloride, Aldehyde, Ketone) setzt sich 2 zu den optisch aktiven Ketonen 12,13, 15 und 16 um. Im Falle der Aldolreaktion mit Propionaldehyd zu 15b entsteht das neue Asymmetriezentrum zu 15 % bevorzugt R-konfiguriert.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197619760724
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  • 5
    Electronic Resource
    Electronic Resource
    α-Heterosubstituierte Organyllithiumverbindungen durch Selen/Lithium-Austausch; gezielte Kopplung von Carbonyl-verbindungen (1977)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1977 (1977), S. 846-858 
    Details
    ISSN: 0075-4617
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: α-Heterosubstituted Organyllithium Compounds by Selenium/Lithium-Exchange; Directed Coupling of Carbonyl CompoundsThe preparation of phenylseleno derivatives 1-4 and 6 is described. Se/Li-exchange with butyl- and tert-butyllithium removes the heteroatom free substituent from 1-3 and 8a; the sulfur derivative 10a undergoes the same transformation. The α-seleno- and α-thioalkyl-lithium derivatives 5 and 11 are generated in high yields from 4 and 6, respectively, as shown by their reactions with carbonyl compounds to give alcohols 12 and 16. According to scheme 1, the allylic alcohols 17, 18, and 20, as well as the olefin 21 and the epoxide 22 are obtained.
    Notes: Die Phenylselenderivate 1-4 und 6 wurden hergestellt.  -  Während beim Versuch der Transmetallierung von 1-3 sowie 8a mit Butyl- oder tert-Butyllithium stets der heteroatomfreie Substituent am Selen ausgetauscht wird, was auch beim Thioether 10a der Fall ist, entstehen aus 4 und 6 die α-Seleno- und α-Thioalkyllithiumderivate 5 bzw. 11. Dies wird durch deren Umsetzung zu den Alkoholen 12 und 16 bewiesen.  -  Nach Schema 1 wurden die Allylalkohole 17, 18 und 20, sowie das Olefin 21 und das Epoxid 22 synthetisiert.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.197719770514
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  • 6
    Electronic Resource
    Electronic Resource
    α,β-Doppeldeprotonierte Nitroalkane: Super-Enamine? Vorläufige Mitteilung (1976)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 59 (1976), S. 2213-2217 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: α,β-Doubly deprotonated nitroalkanes: Super-enamines?At temperatures between -90° and -78° both the α and β-proton of 1-aryl-2-nitro-ethanes (1) are abstracted by n-butyllithium to give the dilithio derivatives of 3. These turn out to be excellent nucleophiles combining with alkyl halides, aldehydes, ketones, and ω-nitro styrenes at the β-nitro carbon atom to give products of type 2. It is shown that 2-nitro-propane undergoes the same double deprotonation and can be coupled with benzaldehyde at one of the β-nitro carbon atoms to yield 4. It is proposed to consider the new reagents as super-enamines 3c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19760590634
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  • 7
    Electronic Resource
    Electronic Resource
    Herstellung von Hilfsstoffen für die asymmetrische Synthese aus Weinsäure. Addition von Butyllithium an Aldehyde in chiralem MediumTeilweise aus den geplanten Dissertationen von G. Crass, W. Langer, H.-A. Oei und M. Schmidt, Universität Giessen. (1977)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 60 (1977), S. 301-325 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of Auxiliaries for Asymmetric Syntheses from Tartaric Acid. Additions of Butyllithium to Aldehydes in Chiral Media.Chiral derivatives of the complexing 1,2-diheterosubstituted ethanes A-D are prepared from tartaric acid. The key starting materials are the succinic acid derivative 1, the dioxolane 2a, and the diamide 3a. These are converted to the ethers, alkoxyamines, and alkylthio-amines listed in the first column of Table 2 which also contains the derivatives 21c, 22d, and 23d made from lactic acid, malic acid, and proline, respectively. It is shown that the highest optical yields (up to 40%) in reactions of butyllithium with aldehydes are obtained when mixtures of (-)-1,2,3,4-tetramethoxy-butane (4b), (+)-2,3-dimethoxy-N,N,N′,N′-tetramethyl-1,4-butanediamine (17a), and (-)-1,4-dimethoxy-N,N,N′,N′-tetramethyl-2,3-butanediamine (14c) with pentane are used at temperatures down to -150° and ratios of auxiliary/butyllithium of up to 10:1 (see equation (1), Tables 2-4).
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19770600202
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  • 8
    Electronic Resource
    Electronic Resource
    CH-Acidität in α-Stellung zum N-Atom in N,N-dialkylamiden mit sterisch geschützter Carbonylgruppe zur nucleophilen minoalkylierung (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 512-526 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: CH-Acidity in α-position to the N-Atom of N, N-Dialkylamides with Sterically Protected Carbonyl Groups Contribution to the Nucleophilic Amino AlkylationSterically protected amides 1 such as the 2,4,6-triisopropyl-benzoic acid derivatives 3, 8b and 10 undergo readily H/Li-exchange with s-butyllithium at the CH3N- or CH2N-groups. The resulting organolithium compounds (cf. 9, 11) are alkylated and hydroxyalkylated with primary haloalkanes, aldehydes, and ketones under chain elongation in the amine position of the amides. The (E/Z)-rotamers of the dialkylamides 7 and 8are separated by chromatography; the amides 4-6, 12, and 13 formally derived from β-hydroxyamines are obtained in the (Z)-form only. The configurational (E/Z)-assignments follow from NMR. and IR. data. The erythro and threo configuration of the two diastereomeric amides 12a and 12b are tentatively concluded from Eu(fod)3-1H-NMR.-shift experiments. The results strongly suggest that the H/Li-exchange takes place regioselectively at the CH—N group which is in cis-position to the C=O double bond (→14). The methyl 2,4,6-tri(t-butyl)benzoate (18) can also be deprotonated to the lithium acyloxymethanide 19 which is trapped by alkylation with 1-iodooctane (→20). - The steric protection of the carbonyl groups in the products 4-8, 10, 12, 13, and 20 prevents their ready hydrolysis to amines and alcohols, respectively. Therefore, triphenylacetic acid derivatives 21 rather than 2,4,6-triisopropylbenzoic acid derivatives for use in the electrophilic substitution of equation (1) are recommended. The trityl group in 21 may be considered a C-leaving-group (C—C protective group, cf. 22, 23). The acetamide 25 reacts readily (→26) and then with electrophiles to give products 27a-c. As shown in the Table, the amides 27 are cleaved under a variety of conditions with formation of triphenylmethane. LiAlH4 produces a tertiary amine, CH3Li a secondary amine, and dissolving alkali metals/naphthalene under aprotic conditions mixtures of secondary amine and its formamide (hydrolysed by acid treatment). Thus the overall process (2) is feasible.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610144
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  • 9
    Electronic Resource
    Electronic Resource
    Three New Chiral Aminoethers from Tartaric Acid for Improved Asymmetric Syntheses with Organolithium Reactions. Preliminary communication (1979)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 62 (1979), S. 2695-2698 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chiral aminoethers 1-4, accessible from tartaric acid, are tested as complexing ligands in organolithium reactions. The tetramine 4 turns out to cause highest inductions [see Table 2 and Equations (1)-(4)].
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19790620819
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  • 10
    Electronic Resource
    Electronic Resource
    Zum stereochemischen Verlauf der elektrophilen Substitution an CH-Gruppen in α-Stellung zum N-Atom behinderter Amide Vorläufige Mitteilung (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 3100-3102 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Sterochemical Course of Electrophilic Substitution at CH Groups in α-Position to the N-Atom of Hindered AmidesIt is shown by 1H-NMR. analysis of the aminoalcohol derivatives 4b and 4c that the lithiation/hydroxyalkylation with acetone of 1-nitroso-and 1-(2,4,6-triiso-propylbenzoyl)-4-phenyl-piperidine leads to configurationally different products. The assigned cis and trans configuration of the substituents in 4b and 4c, respectively, is compatible with the electronic structures 2 and 1, respectively, which were previously proposed for the lithio-derivatives 3 involved in such transformations.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610837
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