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  • General Chemistry  (11)
  • 1995-1999  (11)
  • 1998  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of Hetaryl Glycosides and Their Glycosyl Donor Properties (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1353-1360 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Substitution ; Carbohydrates ; Anomeric O-hetarylation ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Anomeric O-hetarylation of tetra-O-benzyl- and tetra-O-acetylglucose (1a, b) can be directly performed with electron-deficient heteroaromatic/heterocyclic systems 2-14, which contain imide halide moieties. The reactions were carried out in the presence of a base and led, through an exchange of the halide by the glucopyranosyloxy moiety, to the products 2a-14a, 7b-14b. Predominantly or exclusively β-products were obtained. Systems bearing more than one imide halide moiety, such as cyanuric fluoride (15) or 5-chloro-2,4,6-trifluoropyrimidine (16), can be employed for successive anomeric O-hetarylations. Investigation of the glycosyl donor properties of O-glucosyl heteroaromatic imidates with 6-O- and 4-O-unprotected glucose derivatives 18 and 19 as acceptors and comparison of the results obtained with data for the corresponding β-trichloroacetimidates 17aβ and 17bβ, reveals that 2,3,5,6-tetrafluoropyridin-4-yl glucopyranosides 14aβ and 14bβ exhibit similar properties. For specific tasks, for instance α-glucopyranoside formation, 14aβ may even be advantageous.
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  • 2
    Electronic Resource
    Electronic Resource
    Syntheses and Properties of S2-Bridged Benzidines (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2409-2416 
    Details
    ISSN: 1434-193X
    Keywords: Sulfur heterocycles ; Rearrangements ; Reductions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The syntheses of 1,2-benzodithiino[5,4,3-cde][1,2]benzodithiin-2,7-diamine (1) and dithio-bridged benzidine 2 have been achieved. The starting material for the synthesis of 1 was 1,3-diiodo-5-nitrobenzene (15) which was transformed by conventional means into 1,2-bis[3,5-bis(ethylthio)phenyl]diazane (19). The benzidine rearrangement of 19 in the presence of HBF4 at -30 °C yielded 4,4′-diamino-2,2′,6,6′-tetraethylthiobiphenyl (20) in 50 % yield. Treatment of 20 with sodium in ammonia and work-up in the presence of air yielded 1. The latter compound could be reduced with LiAlH4 to the tetrathiol 20a. The starting material for the preparation of 2 was 3-chloro-1-iodo-5-nitrobenzene (23), a side product of the preparation of 15. It was transformed analogously to the preparation of 1 into 1,2-bis(3-ethylthiophenyl)diazane (28). The benzidine rearrangement of 28 in presence of HBF4 at -30 °C afforded 4,4′-diamino-2,2′-bis(ethylthio)biphenyl (29) in 49 % yield. Treatment of 29 with sodium in ammonia and work-up under aerobic conditions yielded 2. Quantitative reduction of 2 to the thiol 29a could be achieved with LiAlH4. The reversible electrochemical reduction of 1 on unmodified glassy carbon electrodes leads to a product to which the structure of 3 was assigned.
    Additional Material: 5 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    The Aluminum-Nitrogen Bond in Monomeric Bis(amino)alanes: A Systematic Experimental Study of Bis(tetramethylpiperidino)alanes and Quantum Mechanical Calculations on the Model System (H2N)2AlY (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1095-1114 
    Details
    ISSN: 1434-1948
    Keywords: Aminoalanes ; Alanes ; Ab initio calculations ; 27Al-NMR spectroscopy ; Structure elucidation ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of metallated nucleophiles MIY [Y = OR, SR, NR2, PR2, AsR2, CR3, Si(SiMe3)3, R = organyl, H] with bis(2,2,6,6-tetramethylpiperidino)aluminum halides [tmp2AlX, (X = Cl, Br, I)] offer facile access to a variety of bis(amino)alanes of the type tmp2AlY. As indicated by 27Al-NMR spectroscopy, mass spectrometry and X-ray crystal structure determina-tions, all of these compounds are monomeric in the solid state, in solution, and in the gas phase. Even Al-E single bonds (E = Si, P, As etc.) that are not commonly encountered are stabilized by the supporting tmp fragments. The results of a systematic analysis of the bonding parameters determined for the tmp2AlY compounds, combined with a quantum mechanical study on model compounds (H2N)2AlY, not only reveal the presence of a highly polar Al-N bond, but at the same time rule out AlN-pp(π) bonding, in contrast to the situation in the analogous tmp2BY compounds. It is shown that the Al-N bond length depends on the acidic character of the protic species HY: the shorter d(Al-N), the less basic is Y.
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  • 4
    Electronic Resource
    Electronic Resource
    Convenient Glycoside Synthesis of Amino Sugars: Michael-Type Addition to 2-Nitro-D-galactal (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1609-1613 
    Details
    ISSN: 1434-193X
    Keywords: Glycals, nitro ; Michael additions ; Glycosylations ; Glycosides, galactosamine ; Reduction, nitro group ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formation of 3,4,6-tri-O-benzyl-2-nitro-D-galactal (3) was readily accomplished starting from tri-O-benzyl-D-galactal (1) by acetyl nitrate addition to 2 and base-promoted acetic acid elimination. Addition of alcohols to 3 under conditions of base catalysis afforded 2-deoxy-2-nitrogalactopyranosides 4a-e in high yields; high α-selectivity was obtained with strong bases, whereas weaker bases furnished mainly the corresponding β-galactopyranosides. Chemoselective nitro group reduction in these glycosides was successfully carried out in the case of disaccharide 4cα using Raney nickel as catalyst, thereby affording after N-acetylation the corresponding 2-acetylamino-2-deoxy derivative 5cα.
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  • 5
    Electronic Resource
    Electronic Resource
    η5-Pentamethylcyclopentadienyliridium(III) and -rhodium(III) Labeling of Amino Acids with Aromatic Side Chains - The Importance of Relativistic Effects for the Stability of Cp*Irııı Sandwich Complexes (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1991-1998 
    Details
    ISSN: 1434-1948
    Keywords: Iridium ; Rhodium ; Amino acids ; Sandwich complexes ; Bioorganometallic chemistry ; Relativistic effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: η5-Pentamethylcyclopentadienyliridium(III) and -rhodium(III) sandwich complexes of the type [(η5-Cp*)M(η6-aa)](CF3SO3)2 (M = Ir, Rh; 3-14) containing L-tyrosine, L-tryptophan and L-phenylalanine derivatives (aa) can be prepared by treatment of [(η5-Cp*)ML3] (CF3SO3)2 [L = thf, (CH3)2CO, CH3CN] with the appropriate bioligand in thf for N-protected compounds and in CF3COOH for α-amino acids with unprotected amino groups. Coordination to the Cp*MIII fragments stabilizes the ketonic form of the tyrosine aromatic side chains, leading to a marked enhancement in the acidity of the p-hydroxy function. The crystal structure of [Cp*Ir(ActyrOMe)] (CF3SO3)2 (3b, ActyrOMe = N-acetyltyrosine methyl ester) confirms a marked distortion towards an η5-oxohexadienyl coordination mode as may be gauged from the tilting of the p-OH plane C13/C14/C15 by no less than θ = 12.9° from that of the remaining ring atoms. Facial isomers are present in an effective 1:1 ratio for all tryptophan derivatives. Whereas the Cp*IrIII sandwich complexes of aromatic α-amino acids are stable in polar solvents, rapid decay is observed for analogous Cp*RhIII complexes of N-unprotected derivatives in polar solvents. Comparative nonrelativistic and relativistic all-electron density functional calculations on the cationic sandwich complexes [Cp*M(η6-C6H5Me)]n+ (n = 2, M = Ir, Rh; n = 1, M = Ru) confirm that all three metals bind more tightly to Cp* than to toluene as gauged by the respective force constants (k1 〉 k2). A much larger relativistic enhancement of k2 for M = Ir (279 vs 207 Nm-1) could be responsible for the greater stability of Cp*IrIII complexes in solution.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Chiral Amide Rotaxanes with Glucose Stoppers - Synthesis, Chiroptical Properties and Wheel-Axle Interactions (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2003-2007 
    Details
    ISSN: 1434-193X
    Keywords: Supramolecular chemistry ; Rotaxanes ; Mechanical bond ; Molecular recognition ; Chirality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In this paper we report on amide rotaxanes with tetrabenzoylglucose stoppers. When acetyl groups are used instead of benzoyl groups, merely a pseudo-rotaxane 5 is obtained. The circular dichroism measurements of the rotaxanes 6a and 6b differ significantly from that one of the free axle 7. Similarly, the Cotton effects of the mixtures of achiral wheels 2a and 2b and chiral axle indicate intermolecular host-guest interactions, likewise. After an addition of a solution of NaOMe the wheel is slipping off immediately and quantitatively by hydrolysis, as the benzoylglucose stoppers decrease in size by hydrolysis.
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  • 7
    Electronic Resource
    Electronic Resource
    Reactions of Dimethyl[tris(trimethylsilyl)methyl]metalanes of Aluminum and Gallium with H2S and Elemental Chalcogens - Crystal Structures of [RAl(μ-S)]2·2 THF, [RGa(μ3-S)]4, [{RAl(μ3-S)}3MeAl(μ3-S)], [RAlMe(μ-SeMe)]2, and [RGaMe(μ-TeMe)]2 [R = C(SiMe3)3] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2033-2039 
    Details
    ISSN: 1434-1948
    Keywords: Aluminum ; Chalcogens ; Cubanes ; Gallium ; Main group elements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the trialkylalane (Me3Si)3CAlMe2 × THF (1) with H2S in toluene at room temperature results in the formation of the dimeric sulfido compound [(Me3Si)3CAl(μ-S)]2 × 2 THF (3), while the reaction of the homologous gallane (Me3Si)3CGaMe2 (2) with H2S under similar conditions affords the heterocubane [(Me3Si)3CGa(μ3-S)]4 (4). Heating of compound 3 in vacuo gives a mixture of the symmetrically substituted [(Me3Si)3CAl(μ3-S)]4 (5) and the unsymmetrically substituted heterocubane [{(Me3Si)3CAl(μ3-S)}3MeAl(μ3-S)] (6). Reaction of the trialkylmetalanes 1 and 2 with elemental selenium in refluxing toluene results in the formation of the corresponding selenolates [(Me3Si)3CMMe(μ-SeMe)]2 (7, M = Al; 8, M = Ga). The compounds exhibit a high thermal stability and can not be converted to the corresponding selenides [(Me3Si)3CM(μ3-Se)]n (M = Al, Ga) upon heating. In contrast, the trialkylalane 1 does not react with tellurium metal in refluxing toluene at all, while the trialkylgallane 2 affords the tellurolate [(Me3Si)3CGaMe(μ-TeMe)]2 (9) under similar conditions. Compounds 3-9 have been characterized by 1H- and 29Si-NMR, mass, and IR spectroscopy. Furthermore, the molecular structures of compounds 3· C6H6, 4· 1.5 C6H6, 6, 7· C6H6 and 9 have been determined by X-ray crystallography.
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  • 8
    Electronic Resource
    Electronic Resource
    Asymmetric Synthesis of β-Methylated Aliphatic Ketones via Lithiated 3-[(S)-2-(Methoxymethyl)pyrrolidino]hex-3-ene⋆ (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1371-1377 
    Details
    ISSN: 1434-193X
    Keywords: Homoenolate equivalents, chiral ; Alkylation ; 1-Aminoallyl anions, chiral ; β-Methyl ketones, chiral ; Asymmetric synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 3-Substituted aliphatic ketones 10 have been obtained in excellent optical yields by alkylation of the aminoallyllithium compound endo-8, a homoenolate equivalent of hexane-3-one, using prolinol ether (SMP) as the chiral auxiliary. The intermediate endo-8 was generated by tin-lithium exchange of the 3-stannylated enamine 7a with butyllithium. An improved hydrolysis procedure for the resulting enamines is described. Some mechanistic implications with respect to the formation as well as the alkylation of endo-8 are discussed.
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  • 9
    Electronic Resource
    Electronic Resource
    The Dimethylmaleoyl Group as Amino Protective Group - Application to the Synthesis of Glucosamine-Containing Oligosaccharides (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2305-2316 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Protecting groups ; Amino sugars ; Glycosylations ; Trichloroacetimidates ; Glycosides, glucosamine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glucosamine was readily transformed into N-dimethylmaleoyl (DMM) protected derivative 1 which furnished trichloroacetimidate 4 as glycosyl donor. Reaction with various acceptors (5a-g) in the presence of TMSOTf as the catalyst afforded the corresponding β-glycosides 6a-g generally in high yields. Cleavage of the DMM group was readily accomplished by treatment with aqueous NaOH and then with HCl (pH 5). Starting from 1 also DMM group containing glycosyl acceptors 9 and 14a-c were synthesized. They furnished with trichloroacetimidates 12 and 4 as glycosyl donors β(1-4)- and β(1-3)-linked disaccharides 13 and 15a-c, respectively. From 18 as galactosyl donor and 14a as acceptor β(1-3)-linked disaccharide 19 was obtained in high yield, which is a versatile building block for the important Galβ(1-3)GlcNAc unit. 19 was transformed into trichloroacetimidate 21; glycosylation with 5e as acceptor gave trisaccharide 22 which furnished on partial deprotection Galβ(1-3)GlcNAcβ(1-4)Glc derivative 24. Thus, the wide applicability of DMM as amino protective group in oligosaccharide synthesis is exhibited.
    Additional Material: 1 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    C-Glycosides of Visnagin Analogues (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2317-2322 
    Details
    ISSN: 1434-193X
    Keywords: C-Glycosyl compounds ; Flavones ; Flavanones ; O-Glycosyl trichloroacetimidates ; Fries rearrangement ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycosylation of the visnagin cleavage product 2 with O-acetyl-protected glycosyl donor 5a afforded O-glycoside 6a, which could be transformed into the O-benzyl-protected compound 6b. The latter underwent Fries-type rearrangement to afford C-glycoside 4b. The same product could be obtained directly from 2 and O-benzyl-protected glycosyl donor 5b. Reaction of 4b with benzaldehyde and anisaldehyde furnished chalcones 7A,B, which, upon treatment with base, furnished flavanone C-glycosides 10A,B. Selenium dioxide oxidation of 10A,B or of 7A,B led to the corresponding flavone C-glycosides 11A,B. The same result was obtained by Baker-Venkataraman rearrangement; on treatment with base, the O-aroyl compounds 12A-C gave C-aroyl compounds 13A-C, which, on addition of TMSOTf, furnished flavone C-glycosides 11A-C. Hydrogenolytic O-debenzylation of 11A afforded target molecule 3A, which was transformed into O-acetyl derivative 14A for characterization. Structural assignments of all compounds were based on 1H-NMR data.
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