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  • 1
    Electronic Resource
    Electronic Resource
    Desoxy-nitrozucker. 2. Mitteilung Herstellung geschützter 1-Desoxy-1-nitroaldosen (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 621-634 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Protected 1-Deoxy-1-nitroaldosesThe direct oxidation of the oxime 1 with t-butyl hydroperoxide and vanadyl acetylacetonate yielding the nitro derivative 2 (54%, Scheme 1) could not be applied to other oximes. Diastereoselective bromination of the aldonolactone oxims 7 and 10-12 according to known procedures gave the corresponding bromonitroso compounds which were oxidized to the bromonitro compounds 9, 14, 18 and 22, respectively. Oxidation of the bromonitroso compound in the D-mannopyranose series proved difficult, but the corresponding chloronitro derivative 23 was easily obtained according to Corey & Estreicher (Scheme 2 and 3). The structure of the bromonitro compound 9 was determined by an X-ray analysis, and the configurations of the bromonitro compounds 14, 18 and 22 were deduced from their molecular rotations. Reduction of the bromonitro compounds gave the protected 1-deoxy-l-nitroaldoses 2, 15/16, 19/20, and 24/25, respectively, in good overall yields. The ribose derivatives 15 and 16 were detritylated to give the nitro compound 4, and the mannose derivative 2 was partially deprotected to give the monoisopropylidene compound 26. The nitro group shows a normal anomeric effect which is reflected in the IR. spectra of the pyranose derivatives 19 and 20, and 24 and 25.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650302
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  • 2
    Electronic Resource
    Electronic Resource
    Total Synthesis of All Eight Stereoisomers of α-Tocopheryl Acetate. Determination of their diastereoisomeric and enantiomeric purity by gas chromatographyDedicated to Professor G. Büchi on the occasion of his 60th birthday (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 1158-1173 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All eight stereoisomers of α-tocopheryl acetate have been synthesized in a state of high chemical and stereoisomeric purity. Key chiral side-chain intermediates were prepared from (+)-(S)-3-hydroxy-2-methylpropanoic acid. New routes to (2R, 4′ RS, 8′ RS)-α-tocopheryl acetate, a mixture of four diastereoisomers, were also developed. A sensitive gas chromatographic method was developed to determine the diastereoisomeric and enantiomeric purity of α-tocopherol samples as the methyl ethers. It was established for the first time that naturally occurring α-tocopherol is essentially a single enantiomer (2 R, 4′ R, 8′ R), synthetic all-rac-α-tocopherol an equimolar mixture of four racemates, and that natural (E)-(7 R, 11 R)-phytol is diastereoisomerically and enantiomerically homogeneous.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640422
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  • 3
    Electronic Resource
    Electronic Resource
    Hydroxyalkylierungen von Cystein über das Enolat von (2R,5R)-2(tert-Butyl)-1-aza-3-oxa-7-thiabicyclo[3.3.0]octan-4-on und unter Selbstreproduktion des CiralitätszentrumsTeilweise in einer vorläufigen Mitteilung publiziert [1]. (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1650-1661 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydroxyalkylations of Cysteine through the Enolate of (2R,5R)-2(tert-Butyl)-1-aza-3-oxa-7-thiabicyclo[3.3.0]octan-4-one with Self-Reproduction of the Center of ChiralityThe heterobicyclic compound 1 specified in the title is readily prepared as a single stereoisomer from (R)-cysteine, formaldehyde, and pivalaldhyde. While it is not possible to generate the enolate 10 from 1 qunatitatively - due to β-elimination of thiolate (→6) - an in-situ addition to aromatic aldehydes such as benzaldehydes (→13-16), pyrrol-, furan-, and thiophen-2-carbaldehydes (→17-19), pyridine-3-carbaldehyde (→21), as well as to other non-enolizable aldehydes like cinnamaldehyde (→22), can be achieved in yields of ca. 50%. The adducts (8 and 9) of lithium diisopropylamide or t-butoxide to these aldehydes are acting, probably as bases for deprotonation and as in-situ sources of the electrophilic aldehyde species (cf. 11, 12). - Of the four possible diastereoisomeric products, one is usually formed with 〉90% selectivity (Table). It is assumed that the preferred stereochemical course of the reaction corresponds to that observed previously with the analogous proline-derived enolate (See 23,24). A chemical correlation with l-α-methyl-β-phenylserine (25) proves the relative configuration of the benzaldehyde adduct 13. All hydroxyalkylated products (13-19, 21, 22) are obtained as crystalline, diastereoisomerically pure compounds and are fully characterized. - The benzaldehyde derivative 13 was used to exemplify the various possible transformations of these products to monocyclic or acyclic amino-acid derivatives such as the oxazolidionenes 26 and 29 (cleavage of the ring containing the S-atom), the thiazolidines 28, 31, and 32 (cleavage of the cyclic N,O-acetal) and the α-branched cysteine 27 and the phenylserines 25 and 30 (cleavage of both rings to give open-chain aminoacids).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670635
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  • 4
    Electronic Resource
    Electronic Resource
    Übergangsmetall-Schwefelylid-Komplexe, XVIII. Die Deoxygenierung von anti-Tricarbonyl(1-methyl-3,5-diorganyl-λ6- thiabenzoloxid)chrom, -molybdän und -wolfram als neuartiger Weg zu λ4-Thiabenzol-Komplexen (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 2022-2027 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Transition Metal Sulfur Ylide Complexes, XVIII. The Deoxygenation of anti-Tricarbonyl(1-methyl-3,5-diorganyl-λ6thiabenzene oxide)chromium,-molybdenum, and -tungsten as a Novel Synthetic Route to λ4-Thiabenzene ComplexesFrom the reaction of anti-configurated λ6-thiabenzene oxide complexes 5a-e, 6e, and 7e with sodium bis(2-methoxyethoxy)aluminium hydride λ4-thiabenzene complexes 2a-e, 3e, and 4a are obtained. The hitherto unknown ylidic heterocycles in the novel complexes behave as significantly stronger donor ligands as the related λ6-thiabenzene oxides as is inferred from spectroscopic data.
    Notes: Bei der Reaktion der anti-Konfigurierten λ6-Thiabenzoloxid-Komplexe 5a-e, 6e und 7e mit Natrium-bis(2-methoxyethoxy)aluminiumhydrid werden die λ4-Thiabenzol-Komplexe 2a-e, 3e und 4e erhalten. Nach den Spektren sind die bisher unbekannten ylidischen Heterocyclen in den neuartigen Komplexen deutlich stärkere Donorliganden als die entsprechenden λ6-Thiabenzoloxide.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831160528
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  • 5
    Electronic Resource
    Electronic Resource
    Untersuchungen an Diazoverbindungen und Aziden, XLII. (Diazomethyl)cyclopropene durch elektrophile Diazoalkan-substitution (1982)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 115 (1982), S. 2965-2980 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigations on Diazo Compounds and Azides, XLII. (Diazomethyl)cyclopropenes by Electrophilic Diazoalkane SubstitutionThe (diazomethyl)cyclopropenes 9 and 10 are formed via electrophilic diazoalkane substitution preferably of diazomethylphosphoryl compounds with cyclopropenylium salts. Either the diazomethyl compounds (7a-c) react with the cyclopropenylium salts 6a-e in the presence of triethylamine (method A) or the metallated diazo compounds 8a-d are combined with the cyclopropenylium bromides 6c-e (method B) (details see table 1). The (diazomethyl)cyclopropenes undergo a novel type of isomerization to pyridazines, partly without heating (9d-f → 11b-d), partly by refluxing in toluene (9a,g → 11a,e as well as 10e,f → 12a,b). The bicyclic betaines 15 and 17 are supposed to be intermediates. The diazomethyl compounds 9a and b yield the α,β- unsaturated ketones 20a and b by acid-catalyzed decomposition.
    Notes: Die (Diazomethyl)cyclopropene 9 und 10 entstehen durch elektrophile Substitution vorzugsweise von Diazomethylphosphorylverbindungen mit Cyclopropenyliumsalzen. Man setzt entweder die Diazomethylverbindungen selbst (7a-c) in Gegenwart von Triethylamin mit den Cyclopropenyliumsalzen 6a-e um (Methode A) oder läßt die metallierten Diazoverbindungen 8a-d mit den Cyclopropenyliumbromiden 6c-e reagieren (Methode B) (Details s. Tab. 1). Die (Diazomethyl)-cyclopropene gehen teils ohne Erwärmen (9d-f → 11b-d), teils beim Erhitzen in Toluol (9a,g → 11a,e sowie 10e,f → 12a,b) eine neuartige Isomerisierung zu Pyridazinen ein; Zwischenstufen sind vermutlich die bicyclischen Betaine 15 und 17. Die Diazomethylverbindungen 9a und b liefern bei der säurekatalysierten Zersetzung die α,β-ungesättigten Ketone 20a und b.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19821150904
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  • 6
    Electronic Resource
    Electronic Resource
    Übergangsmetall-Schwefelylid-Komplexe, XIV. π-Komplexe von 1-Alkyl-3,5-diphenyl-λ4-thiabenzolen mit Dicarbonylnitrosylchrom (1983)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 116 (1983), S. 197-206 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Transition Metal Sulfur Ylide Complexes, XIV. π-Complexes of 1-Alkyl-3,5-diphenyl-λ4-thiabenzenes with Dicarbonylnitrosylchromium1-Alkyl-3,5-diphenyl-λ4-thiabenzene chromium complexes 2a-f are oxidized by NOPF6 in CH2Cl2 at -70°C, yielding the cationic dicarbonylnitrosyl complexes 3a-f. The temperature dependence of the 1H NMR spectra of 3a-f is consistent with a hindered rotation of the ring ligands. The X-ray structure analysis of 3b shows that the molecule in the solid state possesses no local Cs-symmetry.
    Notes: Die 1-Alkyl-3,5-diphenyl-λ4-thiabenzol-Chromkomplexe 2a-f werden durch NOPF6 in CH2Cl2 bei -70°C unter Bildung der kationischen Dicarbonylnitrosyl-Spezies 3a-f oxidiert. Die temperaturabhängigen 1H-NMR-Spektren dieser Komplexe deuten auf gehinderte Rotation der Ringe um das (CO)2(NO)Cr+-Fragment hin. Die Röntgenstrukturanalyse von 3b zeigt, daß das Molekül im Kristall keine lokale Cs-Symmetrie mehr besitzt.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19831160122
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  • 7
    Electronic Resource
    Electronic Resource
    Nucleophilic Aromatic Substitutions. Part XIV.Part XIII, see [1].. Investigation of the mechanism of hydroxy-denitration of 4,2-and 2,4-chloronitrobenzenediazonium ions as a function of pH (1981)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 64 (1981), S. 1777-1789 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 4,2-Chloronitrobenzenediazonium ions in aqueous buffer solutions between pH 2.9 and 7.9 do not hydrolyze by dediazoniation as previous authors have assumed, but by denitration. The isomeric 2,4-compound reacts by denitration (ca. 70%) and dechlorination (ca. 30%). The reactions are general base catalyzed. The products and kinetics are consistent with an SNAr-mechanism in which the general base-catalyzed addition of a hydroxyl group at the reacting C-atom is rate-limiting. The rate maxima at or near the pH-values corresponding to (pK1 + pK2)/2 of the diazonium ⇄ cis-diazotate equilibria can be rationalized on the assumption that the diazonium ion is the only equilibrium form of the diazo compound which enters the substitution proper, and the superposition of the rate term B∑kB[B] of all nucleophiles involved (H2O, OH- and buffer bases).
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19810640607
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  • 8
    Electronic Resource
    Electronic Resource
    On the stereochemistry of allylmetal-aldehyde condensationsPresented at the 185th American Chemical Society National Meeting, Seattle, Washington, March 1983, Abstract no. Orgn. 214.. Preliminary communication (1983)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 66 (1983), S. 1655-1660 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The stereochemical course of the intramolecular allylsilane-aldehyde condensation of 1a has been investigated. A modest preference for the product arising from a synclinal orientation of double bonds was observed with Lewis-acid catalysts. Cyclization induced by fluoride ion resulted in stereochemical reversal.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19830660604
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  • 9
    Electronic Resource
    Electronic Resource
    The Electronic Fine Structure of Co (11)-Complexes with Schiff-Base Ligands (1982)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 65 (1982), S. 2486-2497 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Multiple-scattering-Xα MO-calculations are reported for Co (acacen). The results are essentially in agreement with extended Hückel calculations and EPR. data. Particular emphasis has been placed on the calculation of the electronic structure and one-electron properties, i.e. state energies diagram, spin-orbit coupling and hyperfine coupling based on a ligand field interpretation of the Xα-results, which allow to rationalize the main features of the EPR. spectra.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19820650818
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  • 10
    Electronic Resource
    Electronic Resource
    Alkine und Cumulene, XII. Über die Verwendung von Acetylendicarbonsäure-di-tert-butylester in Diels-Alder-Additionen (1980)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 113 (1980), S. 531-541 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Alkynes and Cumulenes, XII. The Application of Di-tert-butyl Acetylenedicarboxylate in Diels-Alder AdditionsDi-tert-butyl acetylenedicarboxylate (1) may be added in good yields to the model dienes 1,3-butadiene (6a), 2-methyl-1,3-butadiene (6b), 2,3-dimethyl-1,3-butadiene (6c), furan (10), and 1,3-cyclohexadiene (19) to afford the Diels-Alder adducts 7a - c, 12 (E = CO2C(CH3)3), and 20, respectively. Under certain conditions the reaction with 10 also leads to the four 2:1-adducts 13 - 16 (E = CO2C(CH3)3). Whereas the esters 7a - c are converted in quantitative yields to the corresponding anhydrides 8a - c by warming in the presence of catalytic amounts of p-toluenesulfonic acid or by heating in substance, the decomposition of 12 and 20 stops at the stage of the monoesters 17 and 21, respectively. Competition experiments show that 1 is approximately three times less reactive towards 6c than dimethyl acetylenedicarboxylate (11). It is shown that 1 is a useful dienophile for the preparation of “mixed” [2.2]paracyclophanes of type 28.
    Notes: Acetylendicarbonsäure-di-tert-butylester (1) reagiert in guten Ausbeuten mit den Modell-Dienen 1,3-Butadien (6a), 2-Methyl-1,3-butadien (6b), 2,3-Dimethyl-1,3-butadien (6c), Furan (10) und 1,3-Cyclohexadien (19) zu den Diels-Alder-Addukten 7a-c, 12 (E = CO2C(CH3)3) und 20. Im Fall von 10 gelingt unter bestimmten Bedingungen auch die Isolierung der vier 2:1-Addukte 13 - 16 (E = CO2C(CH3)3). Während die Ester 7a - c durch Erwärmen in Gegenwart katalytischer Mengen von p-Toluolsulfonsäure bzw. beim Erhitzen in Substanz quantitativ in die entsprechenden Anhydride 8a - c übergeführt werden können, bleibt diese Zersetzung für 12 und 20 auf der Stufe der Monoester 17 bzw. 21 stehen. Wie Konkurrenzexperimente zeigen, ist 1 gegenüber 6c etwa dreimal weniger reaktiv als Acetylendicarbonsäure-dimethylester (11). Es wird gezeigt, daß 1 ein nützliches Dienophil bei der Darstellung „gemischter“ [2.2]Paracyclophane vom Typ 28 ist.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19801130211
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