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  • Organic Chemistry  (14)
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  • 11
    Electronic Resource
    Electronic Resource
    Totalsynthese von Decarboxybetalainen durch photochemische Ringöffnung von 3-(4-Pyridyl)alaninTeilweise vorgetragen von M.A.S. An der Sitzung der Schweizerischen Chemischen Gesellschaft vom 3./4. Oktober 1975 in Aarau [1]. (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1670-1678 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Total Synthesis of Decarboxybetalaines by Photochemical Ring Opening of 3-(4-Pyridyl)alanineA photochemical approach is presented for the total synthesis of the decarboxybetalaines, which were previously known from the mild decarboxylation of the natural plant colorants, the betalaines: Irradiation of rac-3-(4-pyridyl)alanine (1) yielded the rac-2-decarboxybetalamic-acid-imine (4, 86%), presumably via a Dewar pyridine 2, a cyclic aminal 3 and an electrocyclic ring opening. The imine-zwitterion 4 was treated with three amines, namely (S)-cyclodopa (6), (S)-proline (7), and indoline (8), to afford three decarboxybetalaines, namely (2S)-17-decarboxybetanidine (9, red, 34%), (2S)-13-decarboxyindicaxanthine (10, yellow, 56%), and rac-16-decarboxyindobetalaine (11, orange, 78%), respectively. The structures of these coloring matters were confirmed by their electrophoretic behavior and their spectroscopic properties. 17-Decarboxybetanidine 9 was shown to be a ca. 1:1 mixture of two C(15)-epimers 9a and 9b, separable by chromatography. The configuration of 9a was determined as (2S, 15S) and that of 9b as (2S, 15R), by correlating their optical rotations with those of betanidine (12a) and isobetanidine (12b), respectively. The decarboxybetalaines 9, 10, and 11 did not show the double-bond isomerism at C(β), (Cγ) of the chromophore which had been found characteristic for the corresponding betalaines 12, 13, and 14.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680621
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    Paper (German National Licenses)
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  • 12
    Electronic Resource
    Electronic Resource
    15N-NMR Spectroscopic Characterization of Triaziridines (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 136-140 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 15N-NMR spectra of cis- and trans-2,3-dialkyl-substituted triaziridines are reported. The assignment of the 15N-NMR resonances is described, and the chemical-shift and coupling data are compared with those of aziridines and diaziridines. The 1J(N,H) coupling constants allow one to deduce the relative configuration of the involved N-atom. In CDCl3, a 1J(N,H) value of 58.1 ± 0.5 Hz is assigned to an N—H bond cis to two lone-pairs of electrons at neighboring N-atoms, i.e. to the cis,trans-triaziridinesThe first stereodescriptor denotes the relative configuration of the two equal alkyl substituents, the second the relative configuration of one alkyl substituent and the H-atom., and a value of 51.7 ± 0.5 Hz is assigned to a N—H bond cis to only one lone-pair of electrons, i.e. to trans, cis-triaziridines.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690116
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  • 13
    Electronic Resource
    Electronic Resource
    Synthese von Betenamin und von Betalain-Modellsubstanzen (1986)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 69 (1986), S. 1588-1596 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Betenamine and of Betalaine Model SubstancesFor comparisons of color, spectroscopic properties, pKa values, and stabilities, a number of model substances containing the 1,7-diazaheptamethinium chromophore 8 of the yellow and red betalaine plant pigments were prepared by the thermal or photolytic ring opening of simple pyridine derivatives (such as 2 and 14-16), followed by the introduction of amines. Among the novel compounds prepared were betenamine perchlorate (5), the ‘naked’ ring system of the beet-pigment betanine (C) as well as two 1,7-diazaheptamethinium salts 25 and 27 with terminal amono acids. The synthesis of 5 started with 4-(2-aminoethyl)pyridine (1) and proceeded via 2, ring opening with indoline to 4, saponification, and intramolecular amine replacement (Scheme 1). The syntheses of 25 and 27 involved only one step, namely ring opening of γ-picoline using (S)-cyclodopa (24) and (S)-proline (26), respectively (Scheme 3).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19860690712
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  • 14
    Electronic Resource
    Electronic Resource
    Triaziridine 8. Mitteilung7. Mitteilung: [1].. Zur Acylierung Von Dialkyl-triaziridinen (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 390-395 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: On the Acylation of Dialkyl-triaziridines(2,3-trans)-Diisopropyl- (1) and (2,3-cis)-1,3-cyclopentylenetriaziridine (2) were reacted with ClCOOCH3. In the case of 1, with or without pyridine, an expected acylation at N(1) resulted in the methoxycarbonyl derivative 3. In the case of 2, the reaction in pyridine led to the γ- and α-dihydropyridyl derivatives 5 and 6, respectively, where the acylpyridinium moiety had become attached by a ring C-atom to N(1); without pyridine, it afforded the N-cyclopentenylcarbamates 13 and 14by opening of the triaziridine ring and loss of N2. The mechanisms proposed for these reactions involve the initial attack of an electrophile at N(1) of 1 but at N(2) (or N(3)) of 2. This difference is rationalized with steric factors, inasmuch as the hindrance to an attack at N(2) (or (3)) is greater in i than in 2, whereas this hindrance at N(1) is smaller in 1 than in 2. The greater resistance to opening of the saturated N3-homocycle during acylation of the monocyclic triaziridine 1, as compared to that of the tricyclic one 2, is attributed to greater strain in the latter system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700217
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