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  • General Chemistry  (73)
  • Organic Chemistry  (59)
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  • 1
    Electronic Resource
    Electronic Resource
    Asymmetric Catalysis by Vitamin B12. The isomerization of achiral epoxides to optically active allylic alcohols (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1073-1078 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Achiral epoxides are isomerized to optically active allylic alcohols under the influence of catalytical amounts of cob(I) alamin in protic polar solvents.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710520
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  • 2
    Electronic Resource
    Electronic Resource
    Double-Diamond Inclusion Compounds of 2,6-Dimethylydeneadamantane-1,3,5,7-tetracarboxylic Acid (1991)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 74 (1991), S. 825-877 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of four inclusion compounds of 2,6-dimethylideneadamantane-1,3,5,7-tetracarboxylic acid (4) are described, which involve the following guest species: (a) a mixture of 4-methylpent-3-en-2-one, 2,6-dimethylhepta-2,5-dien-4-one, and mesitylene (condensation products of acetone); (b) mesitylene; (c) a mixture of 4-methylpent-3-en-2-one and mesitylene; (d) (tert-butyl)benzene. In all four cases, the host architectures consist of two interpenetrating super-diamond networks built up by the tetra-acid molecules via pairwise H-bonds between the tetrahedrally directed COOH groups. In the first three cases (tetragonal crystal symmetry), the two diamond-like host lattices interpenetrate symmetrically, in the fourth case (monoclinic) asymmetrically. This asymmetry is brought about by the increased steric bulk of the (tert-butyl)benzene guest molecules. Attempts to enforce an inclusion compound of 4 with a single, extremely hollow diamond-like host lattice by offering still bulkier guest molecules have as yet not been met with success. The generally very high propensity of 4 to form inclusion compounds was envisaged and designed beforehand by appropriate evaluation and modulation of the crystal structure of the parent adamantane-1,3,5,7-tetracarboxylic acid, which represents a fivefold diamond-like self-inclusion compound. Crystals of the free, uncomplexed 4 appear to be extremely unstable and could so far not be obtained. On the other hand, from aqueous solution a very stable monohydrate of 4 may be crystallized (4-H2O), which was also subjected to X-ray analysis. The (triclinic) crystal structure of 4·H2O involves an interesting dichotomy inasmuch its pattern of H-bonding may be rationalized either in terms of a double, cross-linked super-zincblende (sphalerite) architecture, or as a system of porous, puckered 4-connected sheets, which interpenetrate each other pairwise and are cross-linked by the H2O molecules. Various structure and (space group) symmetry characteristics of the supramolecular solid-state complexes reported here are highlighted by pointing out analogies with comparable structures retrieved from the literature.
    Additional Material: 19 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19910740417
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  • 3
    Electronic Resource
    Electronic Resource
    Elektrochemische Bildung von Δ1,2-Norbornen (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 1545-1548 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electrochemical Formation of Δ1,2-NorborneneThe electrochemical reduction of 1,2-dihalogen norbornanes in tetrahydrofuran/furan leads to a mixture of two isomeric cycloadducts 6 and 7. The ratio of these adducts corresponds to those which have been found in reductive bisdehalogenation of 1 and 2 by butyllithium.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610506
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  • 4
    Electronic Resource
    Electronic Resource
    Structural Studies of Crystalline Enamines (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 3108-3135 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Crystal structure analyses of five crystalline enamines together with recently published structural data for two other enamines reveal varying degree of pyramidality at the enamine nitrogen atom. The pyramidality appears to be most pronounced in enamines from piperidine and morpholine, less so in enamines derived from prolinoid amines. A pyrolidine enamine obtained from a derivative of cyclohexane-1,4-dione seems to have a virtually planar enamine group. The implications of these findings for current stereochemical problems in enamine chemistry are discussed.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610839
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  • 5
    Electronic Resource
    Electronic Resource
    Oberflächenmodifikation von Kohlenstoff-Elektroden durch Zweikomponenten-Polymere, aufgebaut aus Epoxidharzen und einem Derivat von Vitamin B1217. Mitt. über Synthese und Reaktionen porphinoider Metallkomplexe. 16. Mitt. s. [1].Herrn Prof. Dr. Albert Eschenmoser zu seinem sechzigsten Geburtstag gewidmet (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1301-1311 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Surface Modification of Carbon Electrodes by Polymers Consisting of Epoxy Resins and a Derivative of Vitamin B12A derivative of vitamin B12 containing a 3,5-diaminobenzoyl group in the c side-chain has been synthesized. It was used as the amine component in the formation of an optically active cross-linked epoxy-polymer. Surface modification of carbon electrodes (basal plane graphite and carbon felt) has been achieved by impregnating them with solutions of the monomers followed by thermal curing at 120°C. Electrochemical responses of the Co(II)/Co(I) redox system from sub-mono to multilayer coverages have been observed. The polymer exhibits catalytic activities typical for monomeric vitamin B12 as shown by spectroscopic and electrochemical techniques. Polymermodified electrodes with large specific surfaces have been used in organic electrosynthesis, i.e. the exclusive formation of valeronitrile by reductive cross-coupling of ethyl iodide and acrylonitrile.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680525
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  • 6
    Electronic Resource
    Electronic Resource
    Reduktive Co-Alkylierung von Heptamethyl-cobyrinat mit dem Methylthiomalonat (S)-Methyl-3-bromo-2-[(ethylthio) carbonyl]-2-methylpropanoatHerrn Prof. Dr. Albert Eschenmoser zum 65. Geburtstag gewidmet (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 1659-1668 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reductive Co Alkylation of Heptamethyl Cobyrinate with the Methylthiomalonate (S)-Methyl 3-Bromo-2-[(ethylthio)carbonyl]-2-methylpropanoateThe methylthiomalonate(-)-(S)-Methyl 3-bromo-2-[(ethylthio)carbonyl]-2-methylpropanoate(5a)was prepared from dimethyl methylmalonate in five steps via the stereospecific cleavage of the (pro-S)-ester group of 1 with pig-liver esterase in an overall yield of 26.5% (Scheme 4a). Reductive Co alkylation of heptamethyl Coβ-perchlorato cob (II)yrinate (8) with 5a by electrosynthesis lead to the alkylcobalt complex 9a in 40% yield (Scheme 4b). The O2-dependent reactions of the methyhnalonyl fragment produced by photolysis of 9a and its deuterated derivative 9c are reported (Scheme 5).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730611
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  • 7
    Electronic Resource
    Electronic Resource
    Influence of the Axial Alkyl Ligand on the Reduction Potential of Alkylcob(III)alamins and Alkylcob(III)yrinates (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 2225-2241 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The irreversible-reduction potentials of 26 alkylcob(III)alamins (RCblIII 1a-z) and 26 alkylcob(III)yrinates (R‘Cby’III; 2a-z) (Ep 1a-z and Ep 2a-z, resp.) have been measured in situ by single-scan voltammetry of hydroxocob(III)alamin hydrochloride (vitamin B12b- HCl; 1) or heptamethyl cob(II)yrinate perchlorate (ClO4‘Cby’II; 2) in presence of the corresponding alkyl halides (RX;3a-z) in DMF. The reduction potentials of alkylcobalt complexes exhibiting half-life times as short as a few seconds become measurable by this technique. Thermodynamic cycles prove that the observed reduction potentials are closely related to the standard reduction potentials E°(R—CoIII + e-⇆R⋅ + CoI). Electron-withdrawing groups and/or an increased degree of substitution at the Co-bound C-atom in RCblIII and, R‘Cby’III shift Ep(1a-z) and Ep (2a-z) towards positive potentials. Linear correlations have been found between Ep(1a-z) (Ep(2a-z)) of RCblIII (R‘Cby’III) and the pKa of RH (or the Taft σ*- or the Hammett σp--values of R) within each class of R, i. e. MeCblIII (Me‘Cby’III), primary RCblIII (R‘Cby’III) and secondary RCblIII (R‘Cby’III). The correlations allow to distinguish between electronic effects of the Co-bound alkyl residues and their steric interactions with the corrin side chains. The correlations have further been used to visualize the light-induced formal insertion of an olefin into the Co, C-bond of an alkylcobalamin (Scheme 2, 1a→1u), a key step in the vitamin-B12-catalized C, C-bond formation.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730820
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  • 8
    Electronic Resource
    Electronic Resource
    Organic Diodes Based on Redox-Polymer Bilayer-Film-Modified Electrodes (1994)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 77 (1994), S. 351-371 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of four electropolymerizable 2,2′-bipyridinium salts with tuned reduction potential (E1∘) is described (N,N′-ethylene-4-methyl-4′-vinyl-2,2′-bipyridinium dibromide (4; E1∘ =-0.48 V), 4-methyl-N, N′-(trimethylene)-4′-vinyl-2,2′-bipyridinium dibromide (5; E1∘= -0.66 V), N,N′-ethylene-4-methyl-4′-[2-(1H-pyrrol-1-yl)ethyl]-2, 2′-bipyridinium bis(hexafluorophosphate) (6b; E1∘= -0.46 V), and 4-methyl-4′-[2-(1H-pyrrol-1-yl)ethyl]-N, N′-(trimethylene)-2,2′-bipyridinium bis(hexafluorophosphate) (7b; E1∘= -0.66 V)). E1∘-Tuning is based on the torsional angle C(3)-C(2)-C(2′)-C(3′), imposed by the N,N′-ethylene and N,N′-(trimethylene) bridge. The vinylic compounds 4 and 5 undergo cathodic, the pyrrole derivatives 6b and 7b anodic electropolymerization on glassy carbon electrodes from MeCN solutions, yielding thin, surface-confined films with surface concentrations of redox-active material in the range 5 · 10-9 〈 Γ 〈 2.10-8 mol/cm2, depending on experimental conditions. The modified electrodes exhibit reversible ‘diquat’ electrochemistry in pure solvent/electrolyte. Copolymerization of 6b or 7b with pyrrole yields most stable electrodes. Bi ayer-film-modified electrodes were prepared by sequential electropolymerization of the monomers. The assembly electrode/poly-6b/poly-7b behaves as a switch, it transforms - as a Schmitt trigger - an analog input signal (the electrode potential) into a digital output signal (redox state of the outer polymer film). Forward-(electrode/poly-7b/poly-6b) and reverse-biased assemblies (electrode/poly-6b/poly-7b) were coupled to the electrochemical reduction of redox-active solution species, e.g. N- (cyanomethyl)-N′-methyl-4,4′-bipyridinium bis(hexafluorophosphate) (8). Zener-diode-like behavior was observed. Aspects of redox-polymer multilayer-film assemblies, sandwiched between two electronic conductors, are discussed in terms of molecular electronic devices.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19940770134
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  • 9
    Electronic Resource
    Electronic Resource
    Struktur eines O, N-Ketenacetals: (1 RS, 8 SR, 10 SR, 4(15)Z)-4-äthyliden-5-oxa-3-azatricyclo [8.4.0.03,8]tetradecanDie C-Atome der äthylidenseitenkette der Titelverbindung 1 sind als C(15) und C(16) (s. Fig. 1) statt systematisch als C(1′) und C(2′) gekennzeichnet. Verbindung 1 kann auch als kondensiertes heterocyclisches Ringsystem benannt werden: 1-äthyliden-perhydro[1,3]oxazixino-[3,4-b]isochinolin. (1980)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 63 (1980), S. 1158-1175 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structure of a O,N-Keteneacetal: (1RS, 8SR, 10SR, 4(15)Z)-4-Ethylidene-5-oxa-3-azatricyclo [8.4.0.03,8]tetradecaneDie C-Atome der äthylidenseitenkette der Titelverbindung 1 sind als C(15) und C(16) (s. Fig. 1) statt systematisch als C(1′) und C(2′) gekennzeichnet. Verbindung 1 kann auch als kondensiertes heterocyclisches Ringsystem benannt werden: 1-äthyliden-perhydro[1,3]oxazixino-[3,4-b]isochinolin.Methods for the preparation of a series of model compounds which were required for stereochemical studies are described: the tricyclic O, N-keteneacetal 1, the two diastereomeric bicyclic amino acids 7 and 10 (see Scheme 2), and the two diastereomeric conformationally fixed tetrahydro-1,3-oxazines (=1,3-oxazixanes) 9 and 11.An x-ray analysis of racemic 1 reveals a quasi-tetrahedral nitrogen pyramid of the O, N-ketene acetal grouping, and an almost perfect conformational analogy between the N- and C-centered allylic positions at the double bond.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19800630507
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  • 10
    Electronic Resource
    Electronic Resource
    Synthesis, Structure, and Redox Chemistry of a Vitamin-B12s-Related Macrocyclic Complex of Cobalt(I)Part 16 on the Synthesis and Reactions of Porphine-Type Metal Complexes. Part 15, see [1]. (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1801-1817 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (±)-[1-hydro-8H-HDP]cobalt(I) 1Full name of 1: [2,2,3,3,7,7,8,8,12,12,13,13,17,17,18,18,-hexadecamethyl-2,3,7,8,12,13,17,18,-octahydro-1H,23H-10,20-diaza-porphinato]cobalt(I); full name of 2a: dibromo[2,2,3,3,7,7,8,8,12,12,13,13,17,17,18,18-hexadecamethyl-2,3,7,8,12,13,17,18-octahydro-1H,21H-10,20-diazaporphinato]cobalt(III).For the nomenclature of [HDP]-complexes see addendum in [2]. is obtained by chemical or electrochemical four-electron reduction of (±)-dibromo- or (±)-dicano[1-hydroxy-8H-HDP]cobalt(III) 2a or 2b4, respectively. The crystal nad molecular structure of 1 was determined by combination of X-ray analysis and MS, 1H-, and 13C-NMR spectroscopy. Square-planar coordinated Co(I) lies closely to the best plane through the four N-atoms which form the first coordination sphere. Thermodynamic data for the coordination of axial bases with the cation of [1-hydroxy-8H-HDP]cobalt 2 in its different metal oxidation states were determined. The pathway of the overall four-electron reduction of 2a to 1 was elucidated: it involves a two-electron reduction of the central metal, a two-electron reduction of the macrocycle accompanied by elimination of the OH-group and final protonation at C(1). Evidence for an intramolecular electron transfer between the central metal and the macrocycle is presented.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670718
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