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  • General Chemistry  (77,717)
  • Cell & Developmental Biology  (25,032)
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  • 201
    Electronic Resource
    Electronic Resource
    Fluorine-Sacrificial Cyclizations as an Access to 5-Fluoropyrazoles (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 823-828 
    Details
    ISSN: 1434-193X
    Keywords: Fluorine-containing heterocycles ; Methyl trifluoropyruvate ; Fluoride elimination ; Cyclizations ; Hydrazone ; Hydrazine tautomerism ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Methyl 3-methoxy-2-trifluoromethylacrylate 1, readily prepared by Wittig reaction from methyl 3,3,3-trifluoropyruvate, has been treated with a number of aryl- (or hetaryl-) hydrazines. Under mild base-catalysis, the resulting 3-hydrazinoacrylates 6 undergo consecutive hydrogen fluoride elimination and intramolecular nucleophilic addition to afford methyl 1-(het)aryl-5-fluoropyrazole-4-carboxylates 7. 5-Aminopyrazoles 8 have been obtained by direct reaction of the ester 7a with a lithium amide, whereas 5-fluoro-1-phenylpyrazole-4-carboxamides 10 have been formed by condensation of the 5-fluoro-1-phenylpyrazole-4-carboxylic acid 9 with amines.
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  • 202
    Electronic Resource
    Electronic Resource
    Preparation of Achiral and of Enantiopure Geminally Disubstituted β-Amino Acids for β-Peptide Synthesis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1-15 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Peptides ; Stereoselectivity ; Chirality ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---While geminally disubstituted α-amino acids are helix-inducing residues in α-peptides, gem-disubstituted β-amino acids are predicted not to fit into any of the three major secondary structures of β-peptides recognized to date [the 314 helix, the 12/10/12 helix, and the pleated sheet (Figure 1)]. In order to be able to synthesize and structurally identify β-peptides containing such building blocks, or consisting entirely of them, and in order to establish the chirality of secondary structures they may form, achiral and chiral gem-disubstituted β-amino acids must be readily available. The methods of preparation of 3-amino carboxylic acids with two carbon substituents at the 2- or 3-position (β2,2-/β3,3-amino acids, Figure 2) are reviewed. While there are numerous essentially classical routes to achiral and rac-β-amino acids of this type (Schemes 1-4), their EPC synthesis is currently the subject of investigations. These include the nucleophilic addition to (R)- or (S)-N-sulfinimines (Schemes 6-10) and other Mannich-type transformations (Schemes 19-22), stereoselective alkylations of various chiral hydropyrimidines (Schemes 11, 12, 18), of esters or amides of 2-cyano-alkanoic acids (Schemes 13, 14, 16), and of Li2 derivatives of non-racemic N-protected 3-amino-alkanoates (Scheme 17), as well as sequences of reactions involving enantiopure gem-disubstituted succinic acid derivatives and a Curtius degradation (Schemes 23-26). Oligomers of the achiral gem-disubstituted compounds 1-(aminomethyl)-cyclopropane and -cyclohexane carboxylic acid have already been shown to form 8- and 10-membered hydrogen-bonded rings, respectively (Figure 5), which provide novel motifs for the possible construction of turns, links, or steps in β-peptidic chains.
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  • 203
    Electronic Resource
    Electronic Resource
    Gabosines L, N and O: New Carba-Sugars from Streptomyces with DNA-Binding Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 149-153 
    Details
    ISSN: 1434-193X
    Keywords: Gabosine ; Secondary metabolite ; Carbohydrates ; Chemical screening ; Biomolecular-chemical screening ; DNA binding ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In addition to the known gabosines A (4), B (5) and C (6), three new gabosines L (1), N (2) and O (3) were detected by chemical screening as secondary metabolites of Streptomyces (strains GT 041230, GT 051024 and S 1096). The constitutions of 1, 2 and 3 were established by spectroscopic techniques and derivatization reactions. The absolute stereochemistry of 1 and 2 was determined by Helmchen's method and has been verified in the case of gabosine N (2) by X-ray analysis. The DNA-binding properties of the gabosines were investigated and analyzed by binding studies using a recently developed thin-layer chromatography technique (bimolecular-chemical screening).
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  • 204
    Electronic Resource
    Electronic Resource
    Dendritic Mixed Hexakisadducts of C60 with a Th Symmetrical Addition Pattern (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 171-180 
    Details
    ISSN: 1434-193X
    Keywords: Dendrimers ; Fullerenes ; Macromolecular chemistry ; Template synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis and complete characterization of dendritic hexakisadducts 8-13 of C60 with a mixed (1:5, 2:4, 3:3 and 4:2) Th symmetrical addition pattern is described. Pentakis-, tetrakis-, tris- and bisadducts 4-7 of C60 with diethyl malonate addends arranged in an incomplete octahedral addition pattern served as core building blocks. Completion of the pseudo-octahedral architecture was achieved by exhaustive cyclopropanation with first- to third-generation bromomalonate dendra 1-3 consisting of the corresponding Fréchet-type 3,5-dihydroxybenzyl alcohol subunits. This concept allows for the convergent synthesis of globular dendrimers with a variable number of dendritic malonates (1-4) and a high dendron density in good yields. The 1H and 13C NMR spectra reflect the Th symmetrical addition pattern of the products and reveal spatial interactions of inner dendron branches.
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  • 205
    Electronic Resource
    Electronic Resource
    Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-trans-3-hexenoic Acids in the Solid State (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 187-192 
    Details
    ISSN: 1434-193X
    Keywords: Hydroxyalkenoic acids ; Hydrogen bonds ; Crystal engineering ; Molecular assemblies ; Scanning force microscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The substituted 6-hydroxy-trans-3-hexenoic acids 2-4 have been prepared by a template coupling reaction between (butadiene)zirconocene, W(CO)6, and cyclobutanone, cyclodecanone, or cyclododecanone, respectively, followed by hydrolytic/oxidative demetallation of the resulting metallacyclic zirconoxycarbene tungsten complexes. The hydroxyalkenoic acids 2-4 have been found to form two novel fundamental types of associated supramolecular structural arrays in the solid state through intermolecular hydrogen bonding, which have been characterized by X-ray diffraction analysis. The cyclobutanone-derived compound 2 exhibits an infinitely extending sheet-like structure, which is composed of symmetrically alternating interconnected 12- and 36-membered rings, each being constructed from the functional groups or frameworks of four individual molecules of 2. In contrast, the cyclodecanone-derived compound 3 adopts a ribbon-type structure composed of C2-symmetrically arranged symmetry-equivalent 15-membered rings, each containing the functionalities from three individual molecules of 2. On the basis of scanning force microscopy studies, the cyclododecanone-derived compound 4 would appear to have a similar structure in the solid state. The structural features of the molecular assemblies that are formed by intermolecular hydrogen bonding of compounds 2-4 in the solid state are selectively controlled by the size and favoured conformations of the spiro-anellated carbocyclic rings at C6 of the 6-hydroxy-trans-3-hexenoic acid carbon chain.
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  • 206
    Electronic Resource
    Electronic Resource
    New Methodologies Based on Arene-Catalyzed Lithiation Reactions and Their Application to Synthetic Organic Chemistry (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 225-237 
    Details
    ISSN: 1434-193X
    Keywords: Lithium ; Arenes ; Catalysis ; Organolithium ; Synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The applications of arene-catalyzed lithiation reactions during recent years are reviewed. This methodology has been used to obtain functionalized organolithium compounds from halogenated as well as nonhalogenated materials, such as heterocycles, sulfones, triflates, ethers, thioethers, amides, and esters. This arene-catalyzed lithiation has also been used in the preparation of polylithiated intermediates. Sub-stoichiometric amounts of the arene may be supported on a polymeric material, its catalytic activity being as efficient as in the solution version.
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  • 207
    Electronic Resource
    Electronic Resource
    Novel Fluorescent Dyes by the Extension of the Core of Perylenetetracarboxylic Bisimides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 365-380 
    Details
    ISSN: 1434-193X
    Keywords: Fluorescent dyes ; Perylenes ; Heterocycles ; NIR dyes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Core-extended perylenetetracarboxylic bisimides were prepared by Diels-Alder reaction followed by reduction, or by nitration followed by cyclisation. Highly fluorescent dyes were obtained with absorption regions from the visible to the NIR. Applications for solar energy harvesting, and quantum counters were suggested.
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  • 208
    Electronic Resource
    Electronic Resource
    Enantioselective Synthesis of the Unsymmetrical Bis(lactone) (-)-(3E,6R,9E,12S,14R)-Colletol Induced by Chiral Sulfoxides and an Approach to (+)-Colletodiol by Asymmetric Hydroxylation of an α,β-Hydroxy Lactone (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 357-364 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Sulfoxides ; Asymmetric hydroxylations ; Lactones ; Sulfoxides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A general synthetic strategy towards the two bis(lactones) (-)-colletol (1) and (+)-colletodiol (2) is described. A common intermediate in this synthesis is the 6-membered hydroxy lactone (+)-(3R,5R)-3-hydroxy-5-hexanolide (6), readily prepared by stereoselective reduction of (+)-(SR)-methyl 3,5-dioxo-6-(p-toluenesulfinyl)hexanoate (7). Stereoselective hydroxylation of this hydroxy lactone has allowed efficient access to (+)-colletodiol (2).
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  • 209
    Electronic Resource
    Electronic Resource
    Palladium(0) Complexes of a 15-Membered Macrocyclic Triolefin as a Recoverable Catalyst - Monomer- and Polystyrene-Anchored Versions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 239-243 
    Details
    ISSN: 1434-193X
    Keywords: Macrocycles ; Palladium ; Polymers ; Catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Preparation of the 15-membered cycle (E,E,E)-1,6,11-tris[(2,4,6-triisopropylphenyl)sulfonyl]-1,6,11-triazacyclopentadeca3,8,13-triene (8) is reported. This cyclic triolefin forms a stable Pd0 complex 9 which catalyzes several cross-coupling reactions and can be recovered. Anchoring to a polystyrene framework affords a solid version of the catalyst, which is recovered by simple filtration and reused without loss of catalytic activity.
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  • 210
    Electronic Resource
    Electronic Resource
    Solution-Dimerization of 4-Aryl-1,4-dihydropyridines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 245-249 
    Details
    ISSN: 1434-193X
    Keywords: Cycloadditions ; Cage compounds ; Dimerizations ; Steric hindrance ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---On irradiation at λ ≥ 270 nm solutions of 4-aryl-1,4-dihydropyridines 1 yield cage dimers 2 as the main products beside small amounts of anti dimers 3. 1H-NMR data and X-ray crystal structure prove centrosymmetrical properties for both dimers with axially orientated 4-aryl substituents. Irradiation with filtered light (λ 〉 313 nm) leads to syn and anti dimers 4 and 3 in nearly equal yields. The poor yields of anti dimers 3 on irradiation with unfiltered light are demonstrated to result from a partial cleavage back to their monomeric starting materials 1.
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  • 211
    Electronic Resource
    Electronic Resource
    Tin-Mediated Free-Radical Cyclization of β-Allenylbenzoyloximes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 275-280 
    Details
    ISSN: 1434-193X
    Keywords: Radical reactions ; Substituent effects ; Nitrogen heterocycles ; Dihydropyridines ; Pyrrolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A set of allene-tethered benzoyloximes (5) has been treated with nBu3SnH. Depending on their substitution pattern, a wide range of compounds has been obtained. If the stannyl radical adds on the allene, the C-centred radical thus formed undergoes either a 5-exo ring closure to give the cyclopentene derivatives 7 or a 6-endo ring closure onto the N atom to give the dihydropyridines 8. If the stannyl radical adds on the benzoyl moiety, an iminyl radical is formed which leads to the 3H-pyrroles 9 and the alkylidene-pyrrolines 10. Steric effects as well as polar effects are the factors governing the reaction course.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99373_s.pdf or from the author.
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  • 212
    Electronic Resource
    Electronic Resource
    Synthesis of Ladder-Type Oligomers Incorporating Phthalocyanine Units (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 303-311 
    Details
    ISSN: 1434-193X
    Keywords: Phthalocyanines ; Cycloadditions ; Ladder Oligomers ; Macrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The condensation of substituted diiminoisoindolines with alkyl-substituted 1,3,3-trichloroisoindolines results in the formation of the highly soluble metal-free phthalocyanines 9, 15. By the same methodology, metal-containing phthalocyanines such as 16, 18 are accessible from suitable metal salts. The precursors 24 and26 were obtained from the phthalocyanine 9 and tetracyclone. The generation of the phthalocyanines 23 and 25 possessing isobenzofuran moieties as diene subunits was accomplished; in the presence of excess 28, the tetracyclone-bisadducts 22 and 24 were transformed into the model compounds 29 and 30, while an excess of 20 or 9 leads to the appropriate trimer-oligomers 31 and 32.
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  • 213
    Electronic Resource
    Electronic Resource
    Syntheses, Structures and Basicities of 1,2,4,5-Tetrakis(dimethylamino)benzene and 2,3,6,7-Tetrakis(dimethylamino)naphthalene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 327-333 
    Details
    ISSN: 1434-193X
    Keywords: “Proton sponge” analogues ; Orientation dependence of hydrogen bonds ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---1,2,4,5-Tetrakis(dimethylamino)benzene (4) and 2,3,6,7-tetrakis(dimethylamino)naphthalene (5) were prepared and structurally determined. Electron-donor functions, protonation, and the geometry of intramolecular hydrogen bonds are discussed. By oxidation of 4 to its dication the benzenoid aromaticity is cancelled in favour of two independent cyanine-type units as determined by X-ray structure analysis.
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  • 214
    Electronic Resource
    Electronic Resource
    Anthracene-Containing [2]Rotaxanes: Synthesis, Spectroscopic, and Electrochemical Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 591-602 
    Details
    ISSN: 1434-193X
    Keywords: Cyclophanes ; Molecular recognition ; Molecular shuttles ; Rotaxanes ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two dumbbell-shaped compounds (8 and 11), each composed of two polyether chains intercepted by a 1,4-dioxybenzene recognition site, terminated by tetraarylmethane-based stoppers, and emanating from a central 9,10- or a 2,6-dioxyanthracene unit, have been synthesized. Two [2]rotaxanes (9 · 4 PF6 and 12 · 4 PF6) have been prepared by interlocking these dumbbell-shaped compounds (8 and 11) with a bipyridinium-based tetracationic cyclophane (15 · 4 PF6) - namely, cyclobis(paraquat-p-phenylene). A [3]rotaxane (10 · 8 PF6) incorporating two cyclophane components (15 · 4 PF6) was also obtained when the 9,10-dioxyanthracene-containing dumbbell-shaped compound (8) incorporating two 1,4-dioxybenzene recognition sites was employed. The 1H-NMR spectroscopic investigation of the [2]rotaxanes (9 · 4 PF6 and 12 · 4PF6) revealed that the cyclophane component encircles one of the two 1,4-dioxybenzene recognition sites in the 9,10-dioxyanthracene-containing [2]rotaxane (9 · 4 PF6) and the 2,6-dioxyanthracene unit in the other [2]rotaxane (12 · 4 PF6). These structures have been confirmed by UV/Vis and electrochemical experiments. Comparison with the spectroscopic properties of simple model compounds shows the presence of electronic interactions which lead to (i) the occurrence of very efficient energy transfer processes in the dumbbell-shaped components and (ii) perturbations in the absorption spectra with appearance of two charge-transfer absorption bands and complete luminescence quenching in the [2]rotaxanes. For the 2,6-dioxyanthracene-containing [2]rotaxane (12 · 4 PF6), it has been demonstrated that the cyclophane can be displaced from the dioxyanthracene to the 1,4-dioxybenzene station upon electrochemical oxidation.
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  • 215
    Electronic Resource
    Electronic Resource
    Replacement of the Cleavable Phosphodiester Bond of a Hammerhead Ribozyme Substrate by an Amide Linkage (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 633-638 
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    ISSN: 1434-193X
    Keywords: Amide linkage ; Phosphodiester ; Hammerhead ribozyme ; Oligonucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A nucleoside dimer in which the natural phosphodiester bond is replaced by an isosteric amide linkage has been prepared. This dimer analogue was subsequently incorporated chemically at the cleavage position of a hammerhead ribozyme substrate. Although the resulting substrate analogue exhibited a high affinity for the ribozyme as shown by gel retardation assays, the amide bond proved to be fully resistant to cleavage under standard conditions of ribozyme cleavage activity.
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  • 216
    Electronic Resource
    Electronic Resource
    Rationally Designed Bicyclic Lactams Control Different Turn Motifs and Folding Patterns in Hexapeptide Mimics (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 695-699 
    Details
    ISSN: 1434-193X
    Keywords: Reverse-turn mimics ; γ-Turns ; β-Turns ; β-Hairpins ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Conformational analysis of N-acetylated hexapeptide mimics incorporating a bicyclic lactam (1-4) was carried out by a combination of 1H-NMR spectroscopy, IR spectroscopy, and computer modeling. The nature of the bicyclic lactam determines the turn motifs and the folding patterns of these constrained peptides. The (5,6)-bicyclic lactam derivatives 1 and 2, characterized by a type-II' β-turn (C=O3···H6-N), are very compact intramolecularly H-bonded structures. The (5,7)-bicyclic lactam derivative 3, characterized by an inverse γ-turn (C=O4···H6-N), is a quite flexible “tweezer-like” structure.
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  • 217
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    Synthesis of [3-D3]-, [3-13C]-, and [1,2-13C2]Propynes and Their Use for the Synthesis of [5-D3-Methyl]-, [5-13C-Methyl]-, and [5,6-13C2-2,5-Cyclohexadienyl]ubiquinones 3 (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 723-727 
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    ISSN: 1434-193X
    Keywords: Isotopic labeling ; Isotopic labeling ; Isotopic labeling ; Deuterium ; Carbon-13 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Three selectively labeled propynes were prepared either with deuterium or carbon-13 at position 3 and doubly labeled with carbon-13 at positions 1 and 2 by an alkylation reaction from the corresponding labeled or unlabeled monolithio acetylides and dimethylsulfates. Their lithiation with nBuLi gave the corresponding propynyllithium derivatives which reacted with dimethyl squarate to afford the corresponding propargylic alcohols. These were thermolysed in p-xylene to furnish [5-D3-methyl]-, [5-13C-methyl]-, and [5,6-13C2-2,5-cyclohexadienyl]ubiquinone. The farnesyl side chain was introduced onto the labeled quinones with farnesyl trimethyltin under BF3 catalysis to provide [5-D3-methyl]-, [5-13C-methyl]-, and [5,6-13C2-2,5-cyclohexadienyl]ubiquinone 3 (6c, 6b, 6a, respectively).
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  • 218
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    Synthesis of Silaproline, a New Proline Surrogate (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 807-811 
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    ISSN: 1434-193X
    Keywords: Proline analogues ; Asymmetric synthesis ; Schöllkopf's method ; Silicon ; Amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The asymmetric synthesis of a new proline surrogate, incorporating the dimethylsilyl group at position 4 of proline using Schöllkopf's bis-lactim ether method, is described.
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  • 219
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    Synthesis and Crystal Structure of Bis(2,3-dihydro-3-methylbenzothiazole-2-ylidene)palladium(II) Diiodide: The First Palladium Complex with Benzothiazole Carbene Ligands Suitable for Homogeneous Catalysis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 869-871 
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    ISSN: 1434-193X
    Keywords: Benzothiazole carbene ; Palladium complex ; Homogeneous catalysis ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The first diiodo palladium complex with nucleophilic benzothiazole carbenes as ligands has been synthesized and characterized. The complex, which is extraordinarily stable towards heat, oxygen, and moisture, has been found to show good catalytic activity in the Heck coupling reaction.
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  • 220
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    Pyrrolidines, Pyrrolines and Pyrroles from 1,4-Diaryl-2,3-dinitro-1,3-butadienes via a 5-endo-trig Cyclization (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 903-912 
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    ISSN: 1434-193X
    Keywords: Dinitrothiophene ; Ring-opening ; Dinitrobutadienes ; Pyrrolidines ; Pyrroles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reactions between 1,4-diaryl-2,3-dinitro-1,3-butadienes 1a-d and primary alkylamines gave high yields of N-alkyl-2,5-diaryl-3-alkylamino-4-nitropyrrolidines 2 as pure all-trans diastereomers via an unusually favoured 5-endo-trig ring closure. The stereochemistry of compounds 2 has been attributed through an X-ray crystal structure analysis of the acetyl derivative 5 of 2ai. Amine elimination from 2 gave the N-alkyl-2,5-diaryl-3-nitro-3-pyrrolines 3 which could be easily aromatized to the corresponding pyrroles 4.
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  • 221
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    Acyl α-L-Rhamnopyranosides, a Novel Family of Secondary Metabolites from Streptomyces sp.: Isolation and Biosynthesis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 929-937 
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    ISSN: 1434-193X
    Keywords: α-L-Rhamnopyranosides ; Secondary metabolites ; Biosynthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---In the course of our chemical screening program, the novel acyl α-L-rhamnopyranosides (1-6) were detected as metabolites from five different strains of Streptomycetes. The structures of all these compounds were elucidated by chemical and spectroscopic methods. The biosynthesis of 1 and 3 was established by feeding 13C-labelled acetate, glycerol, and D-glucose to Streptomyces griseoviridis (strain Tü 3634), and resulted in a complete labelling pattern of the 2,4-dimethyl-3-furanylcarbonyl and benzoyl residues, as well as the rhamnose moiety. These results reveal biosynthetic pathways of general importance and give an insight into the generation of the hexose phosphates, from which deoxysugars are formed. The acyl rhamnosides are members of a novel family of microbial metabolites and are considered as rhamnoconjugates from Streptomycetes.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99413_s.pdf or from the author.
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    Silver-Catalyzed Cyclization of Acetylenic Alcohols: Synthesis of Functionalized 2-Methylene-oxolanes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1019-1025 
    Details
    ISSN: 1434-193X
    Keywords: Silver ; Methylene-oxolanes ; O-Heterocycles ; Enol ethers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Silver salts which have a basic counter-ion are efficient catalysts for the regiospecific intramolecular addition of various acetylenic alcohols. Silver carbonate in aromatic solvent proved to be the best catalyst. Alkynols in which the two reacting parts of the molecule are relatively close together in space required only catalytic amounts of silver ion, while others cyclize readily with stoichiometric quantities. This heterocyclization reaction provides a mild and convenient access to 2-methylene-oxolanes or oxanes.
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    Synthesis of Potentially β-Blocking Practolol Derivatives: (E + Z)-3-[4-(3-Iodoprop-2-enyloxycarbonylamino)phenoxy]-1-(isopropylamino)propan-2-ol (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1007-1012 
    Details
    ISSN: 1434-193X
    Keywords: β-Blockers ; Protecting groups ; Deprotection ; Carbamates ; Oxazolidinone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The iodinatied carbamates 3 (E + Z), with potential β-blocking properties, were synthesized. The first route chosen, from 4-aminophenol and the chloroformate β7, had to be abandoned because of the formation of the oxazolidinone 10 during the epoxidation step. The aminoalcohol 17 prepared from the practolol 1 finally gave the target compounds by condensation with the iodoallylic chloroformates 8 (E + Z). The secondary Boc-protected amine function was regenerated without removing the carbamate function situated in the p-postion, by using mild reaction conditions (1 N HCl).
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    A Facile Solid-Phase Strategy for the Synthesis of Oligonucleotide-Tetraphenylporphyrin Conjugates (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1013-1018 
    Details
    ISSN: 1434-193X
    Keywords: Oligonucleotides ; Conjugation ; Porphyrinoids ; Solid-phase synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A convenient solid-phase synthesis of oligonucleotides conjugated at the 3′-end with a tetraphenylporphyrin residue, by means of a new polymeric support bearing as a linker a lysine derivative, has been developed. A porphyrin linked 17-mer, designed for antisense experiments, has been prepared in good yields, and its hybridization properties with a complementary DNA fragment evaluated by UV thermal analysis.
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    Synthesis of (23R)- and (23S)-23H-Isocalysterols, Marine Sterols with a Cyclopropene Moiety in the Side Chain (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1027-1036 
    Details
    ISSN: 1434-193X
    Keywords: Sterols ; Cyclopropene ; Vinylic bromides ; Vinylsilanes ; Dibromocyclopropanation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A synthesis of (23R)- and (23S)-23H-calysterols 2a and 2b from pregnanoic ester 10 is reported. Alkylation of 10 with dibromide 19b, followed by reduction of the carboethyloxy group to a methyl group, afforded (Z)-vinylic bromide 22. Dibromocyclopropanation of 22 yielded the diastereomeric tribromocyclopropane derivatives 15c and 15d. The corresponding 3-hydroxy-5-ene 17c was transformed into 2a via 25 and a cyclopropenyllithium intermediate. An alternative synthetic route involving vinylsilane 13 and (E)-vinylic bromide 14 has also been examined.
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    Activation of Oximic Nucleophiles by Coordination of Transition Metal Ions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1045-1050 
    Details
    ISSN: 1434-193X
    Keywords: Hydrolysis ; Nucleophilicity ; α-Effect ; Metal ion complexes ; Oximes ; Biomimetic models ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A kinetic study of the reactivity in the cleavage of p-nitrophenyl acetate of a series of 2-pyridineoximes, 1-4, and their complexes with NiII, ZnII and CuII is reported. Complexation of the oximic ligands leads to a remarkable increase in the acidity of the oximic group, following the order CuII 〉 NiII 〉 ZnII. The oximates of free ligands and their metal complexes, being α-nucleophiles, are quite effective in promoting the cleavage of PNPA. However, the reactivity, as defined by the second-order rate constants, is not predictably related to the acidity of the oximic function. The corresponding Brønsted plot shows a linear behaviour up to a pKa value of ca. 8, above which the reactivity of the uncomplexed oximic functions levels off to a limiting value. In the case of the metal ion complexes, a large effect of the ligand structure on the reactivity was observed. As a consequence, complexes of appropriate ligands and metal ions show a reactivity that exceeds the apparent limiting one of the oximates. The origin of such effects and their possible implications in the development of new reactivators of phosphorylated acetylcholinesterase are discussed.
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    Bis[oxo/thioxothiazolinyl] Aromatic Compounds - Synthesis and Conformational Assignment (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1081-1090 
    Details
    ISSN: 1434-193X
    Keywords: Atropisomerism ; Conformation analysis ; Liquid chromatography ; Chiral resolution ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of bis(oxo/thioxothiazolinyl) aromatic atropisomers with two chiral C(aryl)-N(heterocycle) axes was synthesized. The separation of antiparallel, parallel diastereomers was achieved by chromatography on silica. Conformational assignment for the bis-thione atropisomers 1a,b-4a,b and bis-one atropisomers 9a,b-12a,b was based on polarimetric results in analytical chiral chromatography on microcrystalline cellulose triacetate. The relationship conformation-1H NMR chemical shifts, found for the bis-thiones and bis-ones was successfully applied for the conformational assignment of thione-one atropisomers not assigned by chiral liquid chromatography.
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    1,2,3,4-Tetra-tert-butyl-4-trimethylsilyl-4-sila-2-cyclobuten-1-yl: A Quantum Mechanical and ESR Study (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1107-1112 
    Details
    ISSN: 1434-193X
    Keywords: Photochemistry ; Radicals ; EPR spectroscopy ; Quantum mechanical calculations ; Silicon compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Trisilane 7 has been synthesized as a potential photochemical precursor of tetra-tert-butylsilatetrahedrane (5) and/or tetra-tert-butylsilacyclobutadiene (6). Astonishingly, only one Si,Si bond is broken upon irradiation of 7 and the silacyclobutenyl radical 9 can be identified as the reaction product. The structure of radical 9, which in the absence of oxygen is persistent even at room temperature, has been elucidated by comparison of its experimental and calculated ESR spectra.
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    Template-Directed Syntheses, Spectroscopic Properties, and Electrochemical Behavior of [n]Catenanes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1121-1130 
    Details
    ISSN: 1434-193X
    Keywords: Catenanes ; Cyclophanes ; Electrochemistry ; Electronic spectroscopy ; Template-directed synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Catenanes composed of two, three, five, or seven interlocked macrocycles have been synthesized in yields ranging from 1 to 30%. Their template-directed syntheses rely on a series of cooperative noncovalent bonding interactions between π-electron rich 1,5-dioxynaphthalene ring systems and π-electron deficient bipyridinium units which are incorporated within the macrocyclic components. The interlocked structure associated with one of the [3]catenanes was demonstrated unequivocally by single crystal X-ray analysis which also revealed the formation of polar stacks stabilized by intermolecular [π···π] interactions. The number of interlocked components of each catenane was determined by liquid secondary ion, matrix-assisted laser desorption ionization/time-of-flight, and/or electrospray mass spectrometries. The absorption spectra, emission spectra, and electrochemical properties of the macrocyclic components and of the catenanes have been investigated. Two kinds of charge-transfer absorption bands (intramolecular in the cyclophanes containing electron-donor and electron-acceptor units, intercomponent in the catenanes) have been found. Such charge-transfer excited states are responsible for the quenching of the potentially fluorescence units of the cyclophanes, and of the crown ethers in the catenanes. Charge-transfer electronic interactions are also evidenced by the electrochemical behavior. Correlations among the redox potentials of the various compounds are reported and discussed.
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    Chiral Atropisomeric Metalloporphyrins in the Enantioselective Styrene Epoxidation (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1165-1171 
    Details
    ISSN: 1434-193X
    Keywords: Porphyrinoids ; Asymmetric catalysis ; Atropisomerism ; Epoxidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new series of porphyrins has been synthesised, incorporating four identical chiral binaphthyl derivatives in the meso-positions. Owing to a hindered rotation around the bond between the naphthyl and the porphyrin, four atropisomers are generated, which were fully separated by preparative TLC and thoroughly characterised. The free bases were metallated with iron(III) and manganese(III) and the resulting complexes were used as catalytic precursors in styrene epoxidation. The reactions show chemoselectivity and enantioselectivity, depending on the stereochemistry of the metalloporphyrin. It is demonstrated that highest efficiency is performed by the ααββ isomer, showing C2 symmetry.
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    Synthesis and Light-Harvesting Properties of Niphaphyrins (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1193-1197 
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    ISSN: 1434-193X
    Keywords: Porphyrinoids ; Light-harvesting structures ; Energy transfer ; Nanostructures ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The synthesis of niphaphyrins, a new class of rigid, snowflake-shaped porphyrin hexamers designed to mimic the light-harvesting antenna complexes of photosynthetic purple bacteria, is described. In these D6- or D3-symmetric assemblies, six porphyrin macrocycles, as free bases or as zinc chelates, are covalently attached to the six positions of a benzene core through rigid ethynyl linkers. A very efficient singlet excited-state energy transfer has been observed from the Zn chelates to the free-base porphyrin (Fb) chromophores in a niphaphyrin in which three zinc porphyrin chelates alternate with three porphyrin free bases. The overall yield of energy transfer (ΦET) has been estimated as 98%.
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    Synthesis of Novel Functionalized Bi- and Oligopyridines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 543-548 
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    ISSN: 1434-193X
    Keywords: Supramolecular chemistry ; Domino reactions ; Oligopyridines ; Dihydropyridines ; Mannich bases ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An annelation reaction is presented in which 1,3-cyclohexanedione (1) and Mannich bases 6a,b are used for the preparation of functionalized bipyridines 12a, 13a, 14a and dihydropyridine derivatives 10b, 11b. All these products possess a keto group which will allow further transformations. The same concept was applied for the synthesis of the S-shaped terpyridine 25. The reaction of the Mannich base 21 with 1,3-cyclohexanedione yielded the heptacyclic terpyridine 22, which is a key intermediate for the synthesis of torands and other tridentate clefts. The ketone 12a was used for the synthesis of the quaterpyridine 26.
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    π-Conjugated Anions: From Carbon-Rich Anions to Charged Carbon Allotropes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1091-1106 
    Details
    ISSN: 1434-193X
    Keywords: Polycyclic anions ; Aromaticity ; Annulene anions ; Corannulene ; Fullerene anions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Stable π-conjugated anions are formed in the reaction of π-conjugated systems with alkali metals. Reactivity, aromatic properties and aggregation of the anions are described. Bowl-shaped and fullerene anions, as well as helicene and planar polycyclic anions, are discussed vis-à-vis their aromaticity and charge delocalization pattern.
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    Catalytic Asymmetric Aziridination of Enol Derivatives in the Presence of Chiral Copper Complexes to give Optically Active α-Amino Ketones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 557-561 
    Details
    ISSN: 1434-193X
    Keywords: Amino ketones ; Homogeneous catalysis ; Aziridination ; Copper ; Enols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of acyclic and cyclic enol derivatives 1 has been transformed into the corresponding α-amino-functionalized ketones 2 by means of enantioselective catalytic aziridination with chiral Cu complexes, prepared in situ from [Cu(MeCN)4]PF6 and the optically active ligands 3, by using (N-tosylimino)iodobenzene (PhINTs) as a nitrogen source. The best enantioselectivities (ee values of up to 52%) have been achieved for the electronically deactivated enol acetate 1aδ, but the incorporation of steric bulk and the substitution pattern at the enol double bond do not improve the ee values. The cyclic substrates react considerably less readily (only up to 45% conversion) compared to their acyclic counterparts (complete consumption). A transition structure is suggested for the asymmetric Cu-catalyzed aziridination of the enol acetate 1aδ in the presence of the chiral ligand 3b that could account for the sense of the (R)-configured product 2a.
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    Novel Benzotropolone and 2H-Furo[3,2-b]benzopyran-2-one Pigments from Tricholoma aurantium (Agaricales) (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 603-609 
    Details
    ISSN: 1434-193X
    Keywords: Benzopyranones ; (E)-2-Nonenal ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The bright orange-red color of the toadstool Tricholoma aurantium is due to the benzotropolone pigment aurantricholone (1). The compound is at least partially present as the calcium salt. Minor pigments are the yellow 2H-furo[3,2-b]benzopyran-2-one derivatives aurantricholides A (7a) and B (7b), which exhibit strong green fluorescences. Their structures have been established by total syntheses.
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    Photoaddition of Aliphatic Ethers to 4-Methyl-1,2,4-triazoline-3,5-dione: Application to the Synthesis of Functionalized Crown Ethers and Mechanism (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 617-626 
    Details
    ISSN: 1434-193X
    Keywords: Radicals ; Photochemistry ; Aliphatic ethers ; Hydrogen abstraction ; Urazolyl radical ; α-Alkoxy-alkyl radical ; Diones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The photoaddition of 4-methyl-1,2,4-triazoline-3,5-dione (4-MTAD) with a wide variety of acyclic, cyclic and crown aliphatic ethers has been investigated. Monochromatic (λ = 514.5 nm) or polychromatic (λ ≥ 310 nm) irradiations give identical mono-urazolyl ethers as reaction products. Unsymmetrical acyclic ethers afford a mixture of the two α and α′ mono-urazolyl ethers. In the case of 12-crown-4, mono and di-substituted products are obtained. ESR experiments and quantum calculations at the AM1 and 6-31G* levels were performed and a possible reaction mechanism is proposed in which the most probable photochemical process is the H-abstraction leading to a urazolyl radical.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/099269_s.pdf or from the author.
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    Synthesis of Pyridinium Amphiphiles Used for Transfection and Some Characteristics of Amphiphile/DNA Complex Formation (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 665-673 
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    ISSN: 1434-193X
    Keywords: Cationic amphiphiles ; Transfection ; Pyridinium salts ; Vesicles ; Lipoplex ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Pyridinium amphiphiles have found practical use for the delivery of DNA into cells. Starting from 4-methylpyridine, a general synthesis has been devised for the production of pyridinium amphiphiles which allows variation in both the hydrophobic part and in the headgroup area of the compounds. By means of differential scanning microcalorimetry, zeta potential, particle size measurements and cryo electron microscopy, some characteristics of the pyridinium amphiphile/DNA complexes have been determined.
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    Increasing Enantioselectivities and Reactivities by Stereochemical Tuning: Fenchone-Based Catalysts in Dialkylzinc Additions to Benzaldehyde (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1785-1792 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Zinc ; Transition structures ; QM/MM computations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Trimethylsilyl substitutions of the fenchyl alcohols [(1R,2R,4S)-exo-(2-Ar)-1,3,3-trimethylbicyclo[2.2.1]heptan-2-ol, Ar = 2-methoxyphenyl (1) and Ar = 2-(dimethylaminomethyl)phenyl (2)] yield the chiral ligands 3 [Ar = 2-methoxy-3-(trimethylsilyl)phenyl] and 4 [Ar = 2-(dimethylaminomethyl)3-(trimethylsilyl)phenyl]. Increased reactivities and enantioselectivities in diethylzinc additions to benzaldehyde are obtained from 3 (63% ee R) and 4 (93% ee S), relative to 1 (26% ee S) and 2 (73% ee S). X-ray crystal structures of 3 and of its methylzinc complex 3-Zn reveal out-of-plane bending of the methoxy groups as major geometrical consequences of the trimethylsilyl substitutions. Analyses of QM/MM ONIOM μ-O transition-structure models for 1, 2, 3, and 4 show that trimethylsilyl-induced distortions of methoxy and of dimethylaminomethyl groups explain the observed increased enantioselectivities.
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    Enantioselective Preparation of 2,4-Disubstituted Azetidines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1815-1820 
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    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Palladium-catalysed couplings ; Palladacycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Chiral C2-symmetric N-benzylazetidines have been conveniently prepared from optically pure anti-1,3-diols without loss of enantiomeric purity. N-Debenzylation led to the corresponding N-unsubstituted azetidines, which were then subjected to palladium-catalysed coupling reactions with aryl bromides to afford chiral N-arylazetidines. (R,R)-N-Benzyl-2,4-dimethylazetidine has been employed in the synthesis of a new cyclopalladated complex, which can be used, for instance, as a chiral recognition agent for phosphorus ligands.
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    Structure, Biological Activity and Synthesis of Polyamine Analogues and Conjugates (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1841-1863 
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    ISSN: 1434-193X
    Keywords: Polyamines ; Polyamine analogues ; Polyamine conjugates ; Protecting groups ; Protecting groups ; Solid-phase synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and the biological significance of naturally occurring and synthetic polyamine analogues and conjugates are presented and the available methodologies for their synthesis are described. These methodologies involve either the selective functionalization of the amino functions, using suitable protecting groups or acylating agents, or fragment synthesis protocols. The latter employ suitable amino components and simple reactions, like Michael addition to α,β-unsaturated nitriles, alkylation of amines and sulfonamides, reductive alkylation and acylation followed by reduction of the thus-obtained amides, as key-reactions, or azides as key-intermediates, for the assembly of the polyamine skeleton. Syntheses performed in solution as well as in the solid phase are discussed.
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    Biosynthesis of Gabosines A, B, and C, Carba Sugars from Streptomyces cellulosae (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1883-1887 
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    ISSN: 1434-193X
    Keywords: Biosynthesis ; Gabosine ; Bioorganic chemistry ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The biosynthesis of the gabosines A-C (3-5) was studied by feeding cultures of Streptomyces cellulosae subsp. griseorubiginosus (strain S 1096) with 13C-labeled precursors. Although the carba sugars are structurally related to shikimic acid, the biosynthetic origin was found to be different to the shikimate pathway. The results revealed that the gabosines are formed via a pentose phosphate pathway by cyclization of a heptulose phosphate intermediate. This intermediate arises from a triose phosphate by successive transfer of two C2 fragments by transketolases. This pathway is identical as that described for valienamine (7), the aminocarba sugar moiety of validamycin, and acarbose (2). The results from biosynthetic studies are discussed on the background of the variety of gabosines found in nature.
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    Claisen Rearrangement of Allyl Bromofluorovinyl Ethers (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1933-1937 
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    ISSN: 1434-193X
    Keywords: Fluoroalkenes ; Substitution ; Rearrangements ; γ-Unsaturated acids ; Lactones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A one-pot synthesis of α-bromo β-substituted γ-unsaturated acids via a diastereoselective Claisen rearrangement of allyl bromofluorovinyl ethers is described.
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    Near-Infrared and Visible Luminescence from Terphenyl-Based Lanthanide(III) Complexes Bearing Amido and Sulfonamido Pendant Arms (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1923-1931 
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    ISSN: 1434-193X
    Keywords: Lanthanides ; Polydentate ligands ; Luminescence spectroscopy ; Near-infrared luminescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of m-terphenyl-based ligands bearing three coordinating oxyacetate and two amido or two sulfonamido groups, (1a-b)H3 and (2)H3, respectively, have been synthesized and characterized. The structures of the corresponding neutral complexes have been studied using 1H-NMR spectroscopy and luminescence experiments. The photophysical properties of the (1a-b)Eu, (2)Eu, (1a)Tb, and (2)Tb complexes have been studied to determine the structure of the first coordination sphere in methanol. The first coordination sphere consists of eight donor atoms provided by the ligand (three chelating oxyacetate groups and two amide or sulfonamide oxygens), and one methanol molecule. The (1a)Dy and (1a)Sm complexes exhibited sensitized luminescence in the visible spectral region, but the luminescence intensity was very sensitive to quenching by C-H groups. The near-infrared emitting (1a)Ln and (2)Ln complexes exhibited sensitized luminescence at wavelengths (at 880, 1060, and 1330 nm for Nd3+, at 980 nm for Yb3+, and at 1550 nm for Er3+) of interest for applications in optical telecommunication devices. The luminescence lifetimes of these complexes in DMSO and [D6]DMSO are in the range of microseconds. The luminescent state of the NIR emitting lanthanide ions is very efficiently quenched by high frequency oscillators (such as C-H groups) in the solvent and the ligand.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99457_s.pdf or from the author.
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    Condensation of Glyoxal with Triethylenetetraamine; Isomerization and Cyclization (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 33-35 
    Details
    ISSN: 1434-193X
    Keywords: Glyoxal ; Triethylenetetraamine ; Diethyl Oxalate ; Cyclen ; Ring closure ; Isomerizations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The condensation of triethylenetetraamine with glyoxal leads to the formation of four stereoisomers A, B, C, D. A is the thermodynamic product and D the kinetic one. These four compounds exhibit equilibrium and isomerization phenomena which are the key-feature of this cyclen synthesis.
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    Enantiopure Dendrimers Derived from the 1,1′-Binaphthyl Moiety: A Correlation Between Chiroptical Properties and Conformation of the 1,1′-Binaphthyl Template (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 61-71 
    Details
    ISSN: 1434-193X
    Keywords: Binaphthyls ; Chirality ; Circular dichroism ; Dendrimers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The absorption and CD spectra of a series of Fréchet (compounds 7-10) and backfolding (compounds 11-12) dendrimers derived from enantiopure (S)-2,2′-dihydroxy-1,1′-binaphthalene have been recorded (THF) in the range 200-350 nm. All the compounds examined show a positive couplet between 200 and 240 nm (1B transition of the 2-naphthol chromophore), the intensity of which (Δεmax of the low-energy branch) ranges between 100 and 40. By means of the DeVoe polarizability model the intensity of the 1B couplet has been calculated vs. the dihedral angle θ. This analysis provides θ angles of 95-110° for the Fréchet dendrimers and 100-110° for the backfolding compounds. These values clearly indicate that the torsional angle θ, defined by the two naphthalene planes, never exceeds the critical value of 110°. This investigation confirms the wide utility of CD spectroscopy to provide geometrical information that cannot be obtained by other types of structural analysis.
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    Mechanism and Extensibility of the Reaction (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 99-104 
    Details
    ISSN: 1434-193X
    Keywords: Allyl alcohols ; Organocerium reagents ; Alkenes ; Addition reactions ; Cerium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Alkylcerium reagents add to the multiple bonds of allyl and propargyl alcohols in good yields and under mild conditions. The double bond can be reduced with lithium aluminum hydride in the presence of cerium trichloride. The regiochemistry of the attack depends on electronic factors.
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    (S)-Pyroglutamic Acid, (S)-Malic Acid, and (S)-Serine as Useful Starting Materials in the Synthesis of Enantiopure Hydroxyamidines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 115-124 
    Details
    ISSN: 1434-193X
    Keywords: Amidines ; Chiral bases ; N-Acyliminium ions ; Enantioselective catalysis ; Chiral pool ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of four enantiopure hydroxyamidines is described. One amidine was obtained from (S)-pyroglutamic acid. Its key step involved the addition of phenylmagnesium bromide to the corresponding ester, affording the tertiary alcohol without detectable racemization. The second amidine was obtained by coupling of an (S)-malic acid derived N-acyliminium ion with β-naphthol. The other amidines were obtained from an (S)-serine-derived imide which was reduced to two diastereomeric lactams that were eventually transformed into the corresponding amidines.
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    Short Enzymatic Synthesis of L-Fucose Analogs (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 125-132 
    Details
    ISSN: 1434-193X
    Keywords: Aldol condensations ; Carbohydrates ; C-C coupling ; Isomerases ; Controlled ozonolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A short enzymatic route for the synthesis of L-fucose analogs modified at the nonpolar terminus is reported. In particular, fucose derivatives bearing extended linear (1b) and branched (1e) saturated, or various unsaturated (1c, 1d) aliphatic chains have been prepared, in order to increase hydrophobic contacts. The rather general approach involves a sequential application of the recombinant enzymes L-fuculose 1-phosphate aldolase (FucA) and L-fucose ketol isomerase (FucI) from E.coli. Enantiomerically pure L-fucose analogs have been prepared in up to 30% overall yield starting from the appropriate hydroxyaldehyde precursors and dihydroxyacetone phosphate as readily available components. Unsaturated 2-hydroxyaldehydes have been efficiently prepared by alk(en/yn)yl Grignard addition to cinnamaldehyde followed by controlled ozonolysis of the styrene fragment.
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    Efficient Preparation of a Highly Strained Eleven-Membered Ring (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 155-163 
    Details
    ISSN: 1434-193X
    Keywords: Macrocycles ; Cyclizations ; Strained compounds ; Ketophosphonate ; Iodoalkyne ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two strategies have been explored to build the highly strained eleven-membered ring 2, a potential precursor for the biosynthetic key intermediate of the protoilludane family: an intramolecular Horner-Wadsworth-Emmons olefination and an intramolecular Nozaki-Hiyama-Kishi type-ring closure.
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    Chemical Synthesis of a Tetrasaccharide Fragment Related to the Exopolysaccharide of Arthrobacter sp. CE-17 (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 181-186 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Oligosaccharides ; Glycosylations ; Organic synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetrasaccharide 5-aminopentyl glycoside β-D-Manp-(1→4)-β-D-Glcp-(1→4)-α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NH2(22) related to the exopolysaccharide of Arthrobacter sp. CE-17 was synthesized by coupling of the properly protected disaccharide blocks β-D-Manp-(1→4)-β-D-Glcp-1-S-Ph (11) and α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NHZ (20). Building block 11 was obtained by intramolecular β-mannosylation of a malonyl-tethered disaccharide glycoside which was prepared from phenyl 4,6-O-benzylidene-1-thio-β-D-glucopyranoside (1) and ethyl 2,3,4-tri-O-benzyl-1-thio-α-D-mannopyranoside (5) in 5 steps. Building block 20 was obtained by coupling N-Z-protected 5-aminopentyl 2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (14) obtained from the non-benzylated counterpart 12 with ethyl 2,3-di-O-benzoyl-4-O-chloroacetyl-1-thio-α-L-rhamnopyranoside (18) obtained in 3 steps from ethyl 2,3-O-isopropylidene-1-thio-α-L-rhamnopyranoside (15).
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    A New Approach to N-Methylaspartic, N-Methylglutamic, and N-Methyl-α-aminoadipic Acid Derivatives (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 199-204 
    Details
    ISSN: 1434-193X
    Keywords: Hexafluoroacetone ; N-Methylaspartic acid ; N-Methylglutamic acid ; N-Methyl-α-aminoadipic acid ; N-Methylthiazol-4-yl-α-amino acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Methylaspartic acid derivatives and its homologues are obtained by a stereoconservative one-pot procedure from hexafluoroacetone-protected aspartic and glutamic acid, 2a and 2b, respectively. α-Aminoadipic acid (5c) and its derivative 6c are accessible from the corresponding glutamic acid derivative 9b by a Wolff rearrangement. A variety of homochiral N-methylamino acids, 5 and 12, and their derivatives, 6 and 8-11, become readily available by the new synthetic concept.
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    Evidence for the Intermediacy of (η3-Allyl)palladium Complexes in the Palladium-Catalyzed Acryloxylation of Cycloalkenes: Unexpected Oxidation of 1,5-Cyclooctadiene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 219-224 
    Details
    ISSN: 1434-193X
    Keywords: Homogeneous catalysis ; Palladium ; Acetoxylation ; Acryloxylation ; Addition reactions ; Cyclooctadiene ; Cyclooct-4-enone ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Palladium-catalyzed acryloxylation of several cycloalkenes in the presence of the Pd(OAc)2/p-benzoquinone/MnO2 catalytic system is reported. This oxidation reaction yields allylic acrylates as the sole products through the intermediacy of an η3-allyl complex. However, with 1,5-cyclooctadiene (3), cyclooct-4-enone (4) is the major reaction product. Its formation results from oxidation, which is also observed in the palladium-catalyzed acetoxylation of 3. It has been shown that this is the result of a 1,2-trans addition (acryloxy-palladation), followed by a β-hydride elimination, which yields an enol acrylate or acetate. A second Markovnikov-oriented 1,2-trans-acryloxy-palladation on the latter yields a palladium complex, rearrangement of which gives 4.
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    Azido-1,2,3-triphenylpropenes of Varying Stabilities: A Corrigendum of Structure Assignment (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 257-267 
    Details
    ISSN: 1434-193X
    Keywords: Allyl azides ; Vinyl azides ; Azirines ; Rearrangements ; Photochemical cis-trans isomerizations ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A reinvestigation of the reaction between 2,3-diphenyl-2H-azirine (1) and phenyldiazomethane (2) has shown that a literature report has to be corrected since no vinyl azide 4 but rather the allylic compound 3-azido-1,2,3-triphenyl-1-propene (3) is produced. This stable substance, which can also be prepared by substitution reactions of allylic bromide (E)-10 or from alcohol (E)-11, may be separated into its geometrical isomers (E)-3 and (Z)-3, although these equilibrate through rapid [3,3] sigmatropic migration of the azido group. Attempts to synthesize 4 by dehydration of azido alcohols 7 using methanesulfonyl chloride and sulfur dioxide or by elimination of hydrogen chloride from azides 15 led only to 3 and 2-benzyl-2,3-diphenyl-2H-azirine (14). This heterocycle, which can also be prepared by Neber rearrangement, has been found to be the thermal and photochemical decomposition product of the unstable vinyl azides 4. However, dehydrations of 7 using thionyl chloride at low temperature have led to the first isolation of 1-azido-1,2,3-triphenyl-1-propenes (4). Starting with 3 and various other allylic azides, rearrangement reactions involving sigmatropic shift of the azido group or photochemical cis-trans isomerization have been investigated, as have base-catalyzed (prototropic) rearrangements to give vinyl azides.
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    Successive Inclusion of Water, [H3NCH2CH2NH3]2+ and [H3NCH2CH2NH2]+ in the Aromatic Cavity of (p-Sulfonato)calix[4]arene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 133-139 
    Details
    ISSN: 1434-193X
    Keywords: Calixarenes ; Inclusion compounds ; Hydrogen bonds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Titration of the sulfonic protons of (p-sulfonato)calix[4]arene (H8L) with two equivalents of ethylenediamine affords [H3NCH2CH2NH3]2[H4L(H2O)3]·H2O, a molecular complex in which water is included inside the macrocycle. Deprotonation of one of the phenolic groups expels the water molecules from the aromatic cavity, leading to the formation of [H3NCH2CH2NH3]1.5[(H3L)(H3NCH2CH2NH3)]·(H2O)5.5, which represents an unprecedented example of the inclusion of a dication in a calixarene. Further addition of ethylenediamine affords the mixed salt [H3NCH2CH2NH3]2[(H3L)(H3NCH2CH2NH2)]·(H2O)4.5 in which the monocation [H3NCH2CH2NH2]+ is preferentially bound to the cavity through a non-classical hydrogen bond involving an N-H···π facial aromatic contact. Inclusion phenomena are indicated both by NMR and X-ray structure determinations. In the same way as their inorganic-organic counterparts, these clay-like materials are organised into parallel organic-organic layers.
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    Synthesis and Absolute Configuration of Hongoquercin A, an Antibacterial Sesquiterpene-Substituted Orsellinic Acid Isolated as a Fungal Metabolite (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 297-302 
    Details
    ISSN: 1434-193X
    Keywords: Antibiotics ; Configuration determination ; Heterocycles ; Hongoquercin A ; Terpenoids ; Total synthesis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---(±)-Hongoquercin A (1), the racemate of an antibacterial fungal metabolite, has been synthesized starting from geranylacetone (2) and ethyl orsellinate (ethyl 2,4-dihydroxy-6-methylbenzoate, 5). The structure (±)-1 has been confirmed by X-ray analysis of its ethyl ester (±)-10. Synthesis of the naturally occurring (+)-hongoquercin A from (-)-sclareol (11) established its configuration as depicted in 1.
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    Ozonolyses of Cycloalkenes in the Presence of Carbonyl Compounds (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 335-348 
    Details
    ISSN: 1434-193X
    Keywords: Ozonolysis ; Cycloalkenes ; Carbonyl compounds ; Ozonides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ozonolysis reactions of a series of cyclic olefins 1 in the presence of carbonyl compounds 6 provided the corresponding cross-ozonides 42. Further reactions of ozonides 42 with the independently prepared carbonyl oxide +CH2-OO- gave diozonides of structure 43. All of the new ozonides have been isolated as pure substances and characterized by their 1H- and 13C-NMR spectra.
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    Neutral Anion Receptors with Multiple Urea-Binding Sites (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 165-170 
    Details
    ISSN: 1434-193X
    Keywords: Neutral anion receptor ; Hydrogen bonds ; Urea moieties ; Donor-acceptor systems ; Macrocycles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of macrocyclic and acyclic cleft-like anion receptors in which four hydrogen bond donating urea moieties are present in a preorganized fashion is described. NMR spectroscopy shows the complex formation with H2PO4- and Cl -. Cleft-like receptors bind H2PO4- in a 2:1 guest-host stoichiometry (Ka = 107M-2) in DMSO, whereas Cl - is bound in a 1:1 stoichiometry (Ka = 103M-1). The macrocyclic receptors form a 1:1 complex with H2PO4- (Ka = 103M-1 in DMSO) with a 100-fold selectivity for H2PO4- over Cl -.
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    Hydroxylation and Amination of Azulenes by Vicarious Nucleophilic Substitution of Hydrogen (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 193-198 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic substitutions ; Azulenes ; Hydroxylation ; Amination ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Hydroxylation of azulenes with tert-butylhydroperoxide proceeds efficiently at the 6-position when the former contain electron-withdrawing substituents in the five-membered ring. Similarly, VNS amination of azulenes proceeds with 4-amino-1,2,4-triazole; its anion, being an active nucleophile, also reacts with unsubstituted azulene. A variety of transformations of 6-hydroxyazulenes, such as substitution of the corresponding sulfonates with nitrogen, oxygen, sulfur, carbon nucleophiles and halogens, and the Claisen rearrangement of allylic ethers, is reported.
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    Synthesis of Nucleoside Triphosphates that Contain an Aminooxy Function for “Post-Amplification Labelling” (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 211-217 
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    ISSN: 1434-193X
    Keywords: Aminooxy group ; Phosphorylations ; Nucleotides ; Fluorescent labelling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Preparation of the uridine and adenosine triphosphates 1 and 2 bearing a linker with a terminal aminooxy group is described. Both 1 and 2 react readily with the aldehydic fluorescein derivative 15. They could each be incorporated into a 330-mer fragment with T7 RNA polymerase.
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    Reaction of 1,3-Disubstituted Acetone Derivatives with Pseudohalides: A Simple Approach to Spiro[4.4]nonane-Type Bis-Oxazolidines and -Imidazolidines (Bicyclic Carbamates, Thiocarbamates, Ureas, and Thioureas) (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 205-209 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Carbohydrates ; Imidazolidines ; Oxazolidines ; Spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Prochiral 1,3-dihydroxyacetone forms racemic oxazolidine- and oxazoline-type spiro[4.4]nonanes upon reactions with potassium (thio)cyanate and cyanamide. In contrast, 1,3-diaminoacetone yields only the corresponding spiro-bisimidazolidinethione under similar conditions together with monocyclic by-products, but the spiro-bisimidazolidinone is accessible by reaction of 1,3-dichloroacetone with urea. The resolution of the racemic spiro-bisoxazolidinethione 2a was achieved by using brucine as the resolving agent.
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    Synthesis of Chiral Amino Alcohols Embodying the Bispidine Framework and Their Application as Ligands in Enantioselectively Catalyzed Additions to C=O and C=C Groups (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 391-399 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Amino alcohol ; Bispidine ; Enantioselective catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Two generally applicable routes for the synthesis of chiral amino alcohols embodying the bispidine framework have been developed. In linear route A the bispidine framework is built up successively from chiral primary amines via intermediate formation of a piperidinone and a bispidinone. In convergent route B an achiral bispidine is formed first and then the N-substituents are introduced by reaction of the nitrogen bases with chiral electrophiles. In order to determine if the bispidine core and its N-substituents can influence the steric course of enantioselective transformations, bispidine amino alcohols built up by these two routes were investigated as chiral ligands in the enantioselectively catalyzed addition of diethylzinc to aldehydes and chalcone. In general, tridentate ligands containing one chiral amino alcohol fragment and a second amino substituent without a stereogenic center were more efficient than tetradentate ligands with two amino alcohol structural units. With the best ligands the enantioselective addition of diethylzinc to aromatic and aliphatic aldehydes proceeded with 83-98% ee and the nickel-catalyzed addition of diethylzinc to chalcone was achieved with up to 85% ee.
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    Synthesis and Characterization of New Enantiopure 7,7′-Disubstituted 2,2′-Dihydroxy-1,1′-binaphthyls: Useful Ligands for the Asymmetric Allylation Reaction of Aldehydes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 491-497 
    Details
    ISSN: 1434-193X
    Keywords: Binaphthol ; Absolute configuration ; Chiroptical properties ; Enantioselective catalysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---As an extension of our interest in developing new enantioselective reactions based on the binaphthol privileged ligand, we report a simple approach to the synthesis of 7,7′-disubstituted binaphthols. The commercially available 1,7-dihydroxynaphthalene (1) was used as starting material for the preparation of the bromoderivatives 2, which were oxidatively coupled to afford 3, a key intermediate for the preparation of a variety of enantiopure substituted binaphthols (8, 10). The absolute configuration of the new compounds was established by chiroptical analysis and by cholesteric induction. The optically active catalysts derived from the ligands 3, 8, 10, 16 and 17, complexed with Ti(OiPr)2Cl2, Zr(OiPr)4 and ZrCl4(THF)2, were employed for the enantioselective addition of allyltributyltin to aldehydes. Finally, the influence of the substituents of the binaphthyl core on the transmission of the chiral information was also investigated.
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    Synthesis of 4-Arylsulfonylquinolines by Double Condensation of Allyl Aryl Sulfones with Nitroarenes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 521-525 
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    ISSN: 1434-193X
    Keywords: Allyl aryl sulfones ; Nitroarenes ; Condensation reaction ; Lewis acids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Allyl aryl sulfones 2 react with aryl nitrocompounds 1 in a DBU/MgCl2 system giving the 4-arylsulfonyl quinolines 3. Some mechanistic aspects of the reaction are discussed. Application of this reaction to the formal total synthesis of the natural product (-)Eupolauramine is described.
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    Anionic Cyclizations of Pentynones and Hexynones: Access to Furan and Pyran Derivatives (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 527-538 
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    ISSN: 1434-193X
    Keywords: Furans ; Pyrans ; Dihydropyran-2-ylidenes ; Ring closure ; Addition reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---On treatment with base the pentynones 8a-f undergo anionic addition reactions of the resulting enolate species to the alkyne moiety and afford the 2,5-disubstituted furans 10a-f in yields ranging from 10-91%. The proposed mechanism involves the 2-methylene-dihydrofurans 11 as intermediates which tautomerize to yield the observed products. In the case of the α-picolyl derivative 8g both possible enolates 12 and 13 are formed which are subsequently transformed to the products 10g and 14g, respectively. Starting with the hexynones 9a-e an analogous reaction takes place with the formation of the pyran derivatives 15 and 16 in comparable yields. Under the same reaction conditions the n-butyl ketone 9f gives rise to two isomeric compounds, namely the 4H-pyran 16f and the cyclohexenone 17. This result is explained by assuming initial formation of two isomeric enolates which react either by O- or C-attack on the carbon-carbon triple bond.
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    Redox Switchable Ionophores for Heavy and Transition Metal Cations (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 539-542 
    Details
    ISSN: 1434-193X
    Keywords: Crown compounds ; Environmental chemistry ; Cations ; Macrocycles ; Transition metals ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---First examples of new, modular, redox switchable ionophores for heavy and transition metal cations are presented. These systems are based on a crown ether or polyethylene glycol unit substituted by the 1,2,4-thiadiazole/iminoylthiourea redox system (2a-4a, 2b-4b). The syntheses via a Boulton-Katritzki rearrangement are described and their cation selectivities, studied by extraction experiments, proved to be determined by the systems' redox state. Additionally, simple 5-anilino-3-phenyl-1,2,4-thiadiazole (5a) and the corre-sponding iminoylthiourea (5b), which do not contain a potential cation binding polyether substituent were also tested to investigate the complexation property of the redox active building block itself.
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    Addition of Grignard Reagents to Chiral 1,2-Bisimines: A Diasteroselective Preparation of Unsymmetrical 1,2-Diamines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 611-616 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Grignard reactions ; Dynamic kinetic resolution ; Asymmetric synthesis ; Unsymmetrical 1,2-diamines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A diastereoselective synthesis of tert-butyl-1,2-diamines has been developed from the addition of tert-butylmagnesium chloride to the 1,2-bisimines derived from glyoxal and chiral amines such as 1-(S)-ethylphenylamine, 1-(S)-phenylpropylamine or 1-(S)-(p-chlorophenyl)ethylamine. The influence of solvent, temperature and chiral auxiliaries on the chemical reactivity and stereoselectivity has been fully studied. Evidence of a dynamic kinetic resolution during the bis-addition process of the organometallic, leading to the 1,2-di-tert-butylethanediamine,[1] as a single diastereomer, has been demonstrated. This resolution has been applied with high diastereoselectivities to the synthesis of unsymmetrical disubstituted 1,2-diamines, by addition of one equivalent of tert-butylmagnesium chloride, followed by one equivalent of a second Grignard reagent. Several chiral 1-tert-butyl-1,2-diamines have also been synthesized by monoaddition of tert-butylmagnesium chloride to the bisimines, followed by hydride reduction of the chiral intermediate imines.
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    Solid-Phase Synthesis of Dihydropyrans by Eu(fod)3-Catalysed [4+2] Heterocycloaddition of Vinyl Ethers with Benzylidenepyruvic Acid Esters. Comparison with Conventional Homogeneous Liquid Phase Conditions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 639-643 
    Details
    ISSN: 1434-193X
    Keywords: Solid-phase synthesis ; Wang resin ; Hetero Diels-Alder reactions ; Dihydropyrans ; Reductive reactions ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The OH groups of Wang resin were esterified with benzylidenepyruvic acid (1) to give the immobilized 1-oxabutadiene 2. The latter reacted with vinyl ethers 3a-h (dienophiles) in the presence of Eu(fod)3, and the resulting adducts 4a-h underwent reductive cleavage with LiAlH4 to afford the dihydropyrans 5a-h in high (62 to 100%) overall yields. A similar sequence carried out under conventional homogeneous liquid phase conditions led to significantly lower yields. The endo/exo selectivity of the cycloaddition reaction was the same in both cases.
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    Reductive Cleavage of Potential Cholinomimetics Thiadiazolidinones: A New Family of Spiro Compounds (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 675-680 
    Details
    ISSN: 1434-193X
    Keywords: Thiadiazolidinones ; Spiro compounds ; Thiazoles ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The design, synthesis and evaluation of a series of 1,2,4-thiadiazolidinones with potential muscarinic receptor binding properties has been performed. During the synthesis of the target compounds, we observed an interesting reductive cleavage of the thiadiazolidinone system which leads to the formation of the novel piperidine spiro triazine heterocycle. The synthesis, structural elucidation (NMR spectroscopy and X-ray diffraction) and biological evaluation of the new compounds are described. With the structures unequivocally established, a mechanism for the formation of the spiro compound is proposed.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/099462_s.pdf or from the author.
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    Evaluation of the Regioselectivity in Pauson-Khand Reactions of Substituted Norbornenes and Diazabicyclo[2.2.1]heptanes with Terminal Alkynes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 681-689 
    Details
    ISSN: 1434-193X
    Keywords: Pauson-Khand reaction ; Cyclopentenones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---1-Methyl-norbornene ester 9 and 1-methyl-2,3-diazabicyclo[2.2.1]heptene ester 10 were employed in intermolecular Pauson-Khand reactions with various terminal alkynes 11a-f to give the dimethyl 1-methyltricyclo[5.2.1.05,9]dec-7-en-6-one 2,3-dicarboxylates 12 and 13, and diethyl 2,3-diaza-1-methyltricyclo[5.2.1.05,9]dec-7-en-6-one 2,3-dicarboxylates 14 and 15, respectively. Whereas the co-cyclization of norbornene 9 with alkynes 11 bearing small substituents R resulted in the preferred formation of 12 (12:13 ≤ 85:15), regioisomer 13 was obtained as the major product when sterically bulky alkynes were employed (12:13 ≥ 6:94). For 2-methyl-3-butyn-2-ol 11e a strong temperature dependency of the regioselectivity was found. The ratio of regioisomers (12e:13e) changed from 95:5 at -25 °C to 12:88 at 120 °C in toluene. In contrast, reactions with 2,3-diazanorbornene 10 showed only moderate regioselectivities in favour of 14 (14:15 ≤ 69:31), regardless of the temperature and the size of R. The observed regioselectivities support a mechanism for the Pauson-Khand reaction in which the apical rather than the basal anti oriented carbon monoxide ligand of cobalt alkyne complex 1 is replaced by the alkene.
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    On the Regioselectivity of Imidoyl Radical Cyclisations (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 707-711 
    Details
    ISSN: 1434-193X
    Keywords: Radical reactions ; Photolysis ; X-ray scattering ; Rearrangements ; Semiempirical calculations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The previously reported tandem cyclisation of N-aryl α-(2-cyanophenyl)sulfanyl imidoyl radicals affords one quinoxaline derivative arising from exclusive 1,6-cyclisation of the final iminyl radical onto the N-aryl ring. When the imidoyl radicals are generated by addition of photolytically generated (2-cyanophenyl)sulfanyl radicals to isocyanides, the reaction also gives small amounts of a by-product that is formed by an analogous route and whose X-ray crystallographic data are reported here. The formation of this product entails a rare ortho-selective photo-Fries rearrangement of the starting disulfide, followed by addition to the isocyanide and regioselective 1,5-cyclisation of the resulting imidoyl onto only one of the two available radical acceptors, i.e. the cyano group and the sulfide moiety. Semiempirical MNDO-d calculations were performed in order to throw some light on the factors affecting these competitive cyclisations.
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    New Tetrathiafulvalene-π-Spacer-Acceptor Derivatives: Synthesis, Crystal Structure, Optical and Electrochemical Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 737-741 
    Details
    ISSN: 1434-193X
    Keywords: Tetrathiafulvalenes ; Charge transfer ; UV/Vis spectroscopy ; Cyclic voltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---4-[2-tetrathiafulvalenyl-ethenyl]pyridine (1) has been prepared from a Wittig reaction between formyltetrathiafulvalene and 4-picolyltriphenylphosphonium chloride hydrochloride. Conversion of the pyridine moiety of 1 by reaction with methyl iodide leads to 4-[2-tetrathiafulvalenyl-ethenyl]-1-methylpyridinium iodide (2a). Neutralization of 1 with a large excess of L-tartaric acid affords 4-[2-tetrathiafulvalenyl-ethenyl]-1-methylpyridinium hydrogen tartrate (3). These TTF-π-spacer-acceptor compounds have been characterized by elemental analysis, and IR and 1H NMR spectroscopy. The crystal structure of 2a has been determined by X-ray diffraction. The cation is essentially planar. Examination of the bond lengths in 2a, UV/Vis spectra and CV data, and calculations indicate that an intramolecular charge transfer occurs in the studied compounds, although it is rather limited, and larger in 2a and 3 than in 1.
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    Proximate, syn-Periplanar Diazene/Diazene(di)oxy, Diazeneoxy/Diazene(di)oxy, and Diazenedioxy/Diazenedioxy Skeletons: Syntheses, [2+2]Photocycloadditions, Metathesis (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 787-806 
    Details
    ISSN: 1434-193X
    Keywords: Photochemistry ; Heterocycles ; Diazenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Of two very proximate syn-periplanar bisdiazenes (1,2) mono-, di-, tri- and tetra-N-oxides were prepared, representing six combinations of the individual N=N/N=NO/ON=NO chromophores. According to DFT calculations (B3LYP/6-31G*), [2+2]photocycloaddition to the respective oxidized tetrazetidines is significantly to moderately endothermic. The metathesis isomerization of the oxidized tetrazetidines is generally highly exothermic and kinetically increasingly favorable with increasing oxidation state. In practice, four out of the six bichromophoric combinations undergo selectively, in competition with N2 elimination from a DBH unit (13) still partially, metathesis isomerization upon π → π* excitation (monochromatic 254 nm light). In the case of the syn-N=NO/N=NO combinations (5/6, 14), the photoaddition is thermally reversed. For a ON=NO/N=N combination (30), internal electron transfer is responsible for a complex reaction pattern. The preparative value of the metathesis reactions, though, is limited: The metathesis-derived bis[diazene mono(di)oxides] undergo relatively fast secondary photoreactions, while the tri(tetra)oxides undergo rapid thermal transformations. For the N=N/N=NO systems (12), of three potential pathways for its metathesis isomerization, the one that takes place via σ-symmetric intermediates (63, 64) is excluded by virtue of the retention of optical purity in the photometathesis of a highly enriched enantiomer [(-)-12]. Matrix irradiation experiments (12 K, IR control) with 12 result in the appearance of a kinetically highly labile transient. Supported by DFT calculations it is concluded that in the metathesis reactions, the respective tetrazetidine oxides (increasingly destabilized by interactions between oxygen lone pairs and NNσ* orbitals) function as vibrationally excited transients. That thermal reversion of these transients might be a general, nonproductive competition, is suggested by the experimental verification of a “reversed photometathesis” (51 → 15) and by the generally low rates in product formation upon irradiation. The question remains to be answered why in structurally analogous molecular skeletons, [2+2]photocycloaddition occurs in the C=C/N=N and variously oxidized N=N/N=N, and not, however, in the parent N=N/N=N combinations.
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    Remote Anisotropic Effects in Diastereomeric Esters of Fluorinated O-Aryllactic Acids (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 837-840 
    Details
    ISSN: 1434-193X
    Keywords: Chiral auxiliaries ; Analytical methods ; Through-space interactions ; Lactic acid ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The enantiomeric purity of a chiral compound is determined by NMR spectroscopic analysis of the diastereomers formed with a chiral derivatizing agent. Fluorinated O-aryllactic acids (FAC) 1 are efficient chiral reporters, whose spectacular remote anisotropic effects allow an easy identification and measurement of diastereomers. The remote effects are attributed to the particular design of FAC esters relative to other CDAs.
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    Chemo-Enzymatic Synthesis of Thymidine 13C-Labelled in the 2′-Deoxyribose Moiety (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 861-866 
    Details
    ISSN: 1434-193X
    Keywords: DNA ; Dihydroxyacetone monophosphate ; Aldolase ; Carbon-13 ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A synthesis of [3′,4′-13C2]thymidine (1) is described in which [13C2]acetic acid (2) is converted into the nucleoside in twelve steps with 9% overall yield. D-2-Deoxyribose-5-phosphate aldolase (DERA, EC 4.1.2.4) and triosephosphate isomerase (TPI, EC 5.3.1.1) are used for the stereocontrolled formation of D-[3,4-13C2]-2-deoxyribose-5-phosphate (8) from [2,3-13C2]dihydroxyacetone monophosphate (DHAP, 7) and acetaldehyde in 80% yield. The route permits the introduction of isotopically enriched carbon atoms at any position or combination of positions in the furanose ring and the product can be coupled with any of the four naturally occurring base moieties.
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    Asymmetric Synthesis of α-Substituted β-Amino Sulfones by Aza-Michael Addition to Alkenyl Sulfones and Subsequent α-Alkylation (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 879-892 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Addition reactions ; Sulfones ; Alkylations ; Amines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The aza-Michael addition of enantiopure 1-aminopyrrolidines to (E)-alkenyl sulfones in the presence of a catalytic amount of ytterbium trifluoromethanesulfonate [Yb(OTf)3] yields β-hydrazino sulfones in moderate to good yields and with diastereoselectivities of up to ≥ 98%. The latter undergo reductive N-N bond cleavage with BH3 · THF and, after N-protection with Boc2O or benzyl bromide, afford N-protected β-amino sulfones with moderate to high enantiomeric excesses (ee = 42 to ≥96%) without racemization. Subsequent α-alkylation of the N,N-dibenzyl protected β-amino sulfones with various electrophiles yields α-alkyl-β-amino sulfones in excellent yields (88-97%) with high diastereomeric (de ≥96 to ≥98%) and enantiomeric purity (ee = 94 to ≥96%). The absolute configuration of the new stereogenic centre was determined by X-ray structural analysis and confirmed by NMR spectroscopy (NOE experiments). Possible reaction mechanisms for the conjugate addition and α-alkylation are presented.
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    Products, Rates, and Mechanism of the Gas-Phase Condensation of Phenoxy Radicals between 500-840 K (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 921-928 
    Details
    ISSN: 1434-193X
    Keywords: Gas-phase chemistry ; Phenoxy radicals ; Dioxins ; Phenoxyphenols ; Reaction mechanisms ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Phenols are demonstrated precursors of “dioxins” - polychlorinated dibenzo-p-dioxins (DDs) and dibenzofurans (DFs) - in thermal processes, especially incineration. Heterogeneous catalysis, depending on conditions, can play an important role, but mere gas-phase combination of phenolic entities to ultimately DD and/or DF is always possible. The present paper addresses the fundamental role of phenol itself. Phenol has long been known to give DF upon pyrolysis and in similar thermal reactions. In the liquid phase under oxidative conditions it yields five condensation products (A-E); this clearly occurs through the dimerization of two phenoxy (PhO) radicals, followed by enolisation/rearomatisation. Our study shows that in the gas phase, at the lower T end, such dimers are also formed, but still with very little DF. That DF, indeed, is almost the only condensation product at elevated temperatures is substantiated by thermochemical-kinetic analysis (favouring the pathway of ortho-C/ortho-C combination of two PhO radicals), as well as by results obtained with two plausible intermediates, viz. 2,2′-dihydroxybiphenyl (A) and 2-phenoxyphenol (C). Mechanisms for the requisite enolisation and dehydration steps leading to DF are discussed.
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    Synthesis of (S)-9-Methylgermacrene-B, the Male-Produced Sex Pheromone of the Sandfly Lutzomyia longipalpis from Lapinha, Brazil, and Its (R)-Isomer (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 955-962 
    Details
    ISSN: 1434-193X
    Keywords: Leishmaniasis ; Pheromones ; Pheromones ; Terpenoids ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Both the enantiomers of 9-methylgermacrene-B (1) were synthesized from the enantiomers of methyl 3-hydroxy-2-methylpropanoate (2). The male-produced sex pheromone of the sandfly Lutzomyia longipalpis (the vector of the protozoan parasite Leishmania chagasi) from Lapinha, Brazil, was identified as (S)-1 by GC comparison.
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    Studies Towards the Synthesis of Aplykurodins - Synthesis of 17,18-Dihydro-3,9-di-epi-aplykurodinone B (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 439-448 
    Details
    ISSN: 1434-193X
    Keywords: Aplykurodins ; Marine steroids ; C-C coupling ; Cyclic peroxides ; Lactonization ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---An approach to the synthesis of aplykurodins, ichthyotoxic marine lactones, is presented. The carbon framework was derived from vitamin D3 by conversion of the readily accessible allyl alcohol 13 to the protected Grundmann's hydroxy ketone 22 and subsequent introduction of the C2 side chain through a Pd0-promoted coupling. Highly stereoselective hetero Diels-Alder reaction with O21 produced the key intermediate peroxide 25. Functional group transformations, coupled with a series of chemo- and stereoselective reactions, finally resulted in the synthesis of the unnatural analogue 17,18-dihydro-3,9-di-epi-aplykurodinone B (6).
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    Oxidation of Aryl- and Diarylcyclopropanes in a Pentasil Zeolite: Ring Opening with Deprotonation or Net Hydrogen Migration (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 467-472 
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    ISSN: 1434-193X
    Keywords: Zeolites ; Radical ions ; Ring opening ; Electron transfer ; Oxidations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Incorporation of trans-1,2-diphenylcyclopropane (1) and its 3,3-D2-isotopomer into the channels of a redox-active pentasil zeolite (Na-ZSM-5) resulted in the formation of exo,exo-1,3-diphenylallyl radical (2•) and its 2-D1 isotopomer, respectively. This conversion requires oxidation, ring opening, and deprotonation, in an unspecified sequence. The allyl radical 2• is also formed upon incorporation of trans-1,3-diphenylpropene (3). A comparison with the solution photochemistry, in the presence or absence of added base, shows the conversion of 1 into 2• to be a zeolite-specific reaction. Incorporation of arylcyclopropanes 9 (R = H, OCH3) into ZSM-5 generated trans-propenylbenzene radical cations 10•+ (R = H, OCH3); the 2,2-D2 isotopomer of 9 (R = OCH3) gave rise to three different isotopomers of 10•+ (R = OCH3).
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    Syntheses of Novel Tripodal Calix[n]cryptands (n = 4, 6) and Their Extraction Abilities toward Cations (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 485-490 
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    ISSN: 1434-193X
    Keywords: Calixarenes ; Tripodal cryptand ; Extraction abilities ; Cations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tripodal calixcryptands have been one of the scarcely explored fields in calixarene chemistry due to the difficulties in their preparation. The strategy presented in this paper shows that novel tripodal calixcryptands can be conveniently prepared by directly treacing p-tert-butylcalix[n]arenes (n = 4, 6) with a multi-functional polypode reagent, e.g. 1,1,1-tris(tosyloxyethoxyethoxymethyl)propane or tetrakis(tosyloxyethoxyethoxymethyl)methane, under selected conditions. The first example of 1,2,4-tripodal calix[6]cryptands has been prepared. Novel calix[6]crown and doublecalix[4]arenes were co-prepared. The extraction abilities of these novel calixcryptands toward several alkali metal ions, ammonium and alkylammonium ions are presented.
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    Synthesis of α- and β-Substituted Aminoethane Sulfonamide Arginine-Glycine Mimics (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1219-1228 
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    ISSN: 1434-193X
    Keywords: Peptidomimetics ; Peptidosulfonamides ; Peptidomimetics ; Transition-state isosteres ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -In this paper we present a synthesis of both α- and β-substituted aminoethane sulfonamide arginine mimics. The α-substituted sulfonamides were obtained starting from an alkene, whereas the β-substituted sulfonamides were derived from an amino acid derivative.
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    Nucleophilic Additions of Sodium Alkoxides to 4,4-Dichloro-1,1-diphenyl-2-azabuta-1,3-diene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1235-1239 
    Details
    ISSN: 1434-193X
    Keywords: Nucleophilic additions ; Nucleophilic substitutions ; Azabutadienes ; Δ2-Oxazoline ; Azabutenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The reaction of some sodium alkoxides with 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene is described. Whereas sodium methoxide, ethoxide or isopropoxide leads to 1,3-bis(alkoxy)- and/or 1,3,4-tris(alkoxy)-2-azabut-2-enes, the sodium salt of ethyl glycolate gives a Δ2-oxazoline. Mechanisms for the formation of these products are proposed.
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    Isolation and Structural Elucidation of Steroid Oligoglycosides from the Starfish Asterias rubens by Means of Direct Online LC-NMR-MS Hyphenation and One- and Two-Dimensional NMR Investigations (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1253-1262 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Starfish ; LC-NMR-MS hyphenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -LC-NMR-MS hyphenation has been applied in the screening of an asterosaponin subfraction obtained from the starfish Asterias rubens for unknown compounds. The suitability of this technique for characterizing compounds in the molecular weight range of 1200 to 1400 a.m.u. has been demonstrated. The additional information concerning the number of exchangeable protons provided by the LC-NMR-MS experiment proved to be particularly valuable for the structural elucidation. The LC-NMR-MS screening indicated the presence of hitherto unknown asterosaponins in the sample. Based on this information, four new compounds (ruberosides A-D; 2-4 and 6) have been isolated and their structures have been elucidated using one- and two-dimensional NMR techniques. A minor component has tentatively been assigned the structure 5.
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    Unexpected Rearrangements of Bicyclic Pyrazolines Derived from 6,6-Diphenylpentafulvene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1271-1278 
    Details
    ISSN: 1434-193X
    Keywords: Diphenylpentafulvene ; Diarylnitrilimines ; Regioselectivity ; Quinolines ; Pyrazole ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -New quinoline and pyrazole derivatives are obtained after the acid-promoted intramolecular rearrangement of regioisomeric pyrazolines resulting from the cycloaddition of 6,6-diphenylpentafulvene with diarylnitrilimines.
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  • 285
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    Stereoselective Synthesis of carba- and C-Glycosyl Analogs of Fucopyranosides (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1285-1296 
    Details
    ISSN: 1434-193X
    Keywords: Carbocycles ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Fucopyranoside analogs with methylene groups instead of endo- or exo-anomeric oxygens, carba- and C-fucopyranosides, respectively, were synthesized. For the synthesis of 5a-carba-L-fucose (1) two approaches were studied, which shared a common cyclitol building block (8), obtained from a SmI2-promoted carbocyclization of a D-mannitol derivative. The first route made use of a Stork radical cyclization onto a conduritol derivative 13 as the key step, which failed to give the silyl ether ring. The second route furnished the target 1, and involved regioselective elimination of a cyclic sulfate 9, and stereoselective hydrogenation of a double bond, controlled by substitution on the substrate. For the synthesis of 1-C-fucopyranosides (37, 38, and 42) a new method based on the use of fucosyl phenyl sulfoxides (35 and 41) was employed. An anomeric carbanion is generated through phenylsulfinyl-lithium exchange, which reacted with electrophiles with retention of configuration at the anomeric center. The required fucosyl sulfoxides were prepared from L-fucose by highly stereoselective thioglycosylation reactions.
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    Synthesis of (3S,7S)- and (3S,7S,15S)- Stereoisomers of 3,7-Dimethyl-2-heptacosanone and 3,7,15-Trimethyl-2-heptacosanone, the Ketones Identified from the Locust Schistocerca gregaria (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1307-1312 
    Details
    ISSN: 1434-193X
    Keywords: Ketones ; Pheromones ; Pheromones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The (3S,7S) and (3S,7S,15S) stereoisomers of 3,7-dimethyl-2-heptacosanone (1) and 3,7,15-trimethyl-2-heptacosanone (2), the ketones identified from the locust Schistocerca gregaria, were synthesized by employing (2R,6S)-7-acetoxy-2,6-dimethyl-1-heptanol (4) as the starting material.
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  • 287
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    Asymmetric Synthesis of 1,4-Disubstituted Tetrahydroioquinolines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1319-1325 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric synthesis ; Tetrahydroisoquinolines ; Cyclizations ; Diastereoselective alkylation of Amides ; Phenylglycinol ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Bischler-Napieralski cyclisation of optically active β-substituted phenylethylamines 4a-c followed by diastereoselective reduction led to 1,4-disubstituted tetrahydroisoquinolines 6a-c and 8a-c. The same methodology afforded the 4-benzyl pyrroloisoquinolines 10.
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    Kinetics of Photochemical Reactions of Thionine with Thiourea (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1345-1351 
    Details
    ISSN: 1434-193X
    Keywords: Kinetics ; Photochemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The photochemical reaction of thionine (Th) with an organic reductant such as thioureas was studied in absolute methanol at constant temperature 25±0.1°C. Spectrophotometric methods were adopted for the determination of the values of absorbances in the presence of extremely dissociated, undissociated and partially dissociated acridine in absolute methanol. The acidity of the reaction solution H0 was controlled by using acetate buffer solutions. The effect of variables like concentration of thiourea, acidity and temperature on quantum yield (φ) was studied and the results were interpreted in terms of reaction mechanism. It was found that the quantum yield of the reactions of thionine with thiourea is controlled by two equilibria between (i) triplet state of thionine with proton and protonated triplet state of thionine, and (ii) protonated triplet state of thionine with reductant and associated complex (Th·H2T++·AH2).
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    Addition of Grignard Reagents to Chiral 1,2-Bisimines: A DiasteroselectivePreparation of Unsymmetrical 1,2-Diamines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1373-1373 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -No Abstract.
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    Atropisomeric Transition State Analogs (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1365-1372 
    Details
    ISSN: 1434-193X
    Keywords: Atropisomerism ; Transition states ; Enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Transition state mimicry is one of the most powerful concepts in enzyme inhibitor design and has led to the development of catalytic antibodies. Transition state analogs are compounds with a fixed shape that resemble the geometry and charge distribution of the transition state of a given reaction. Stabilization of a transition state like conformation is most often achieved by incorporating a ring system into the analog. We show herein that atropisomerism can be used as a new principle for enforcing a transition state like conformation. Atropisomerism relates to the existence of stereoisomers of structurally constrained molecules due to a frozen rotation about a single bond, as for example in binaphthol. The 1-aminomethylnaphthalene derivative 1 exhibits atropisomerism due to a frozen rotation about the C(1)-C(methylene) single bond, which holds the dihedral angle θ[C(2)-C(1)-C(methylene)-N] close to 90°. Compound 1 mimics the transition state for hydride transfer between 1,4-dihydroquinolines 4 and acetone.
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    Single Electron Transfer vs. SN2 Reaction (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 713-721 
    Details
    ISSN: 1434-193X
    Keywords: Reductive alkylation ; Acenaphthylenes ; Carbanions ; Polycycles ; Single-electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Reaction of the 5-hydroacenaphthylene anion with benzyl halides proceeds at carbon atom 1 as well as at carbon atom 2a, in the latter case creating a quaternary centre. The hardness-softness of the electrophiles was shown to play only a minor role in determining the regioselectivity of the reaction of the hydroanion with several benzyl and alkyl halides: the leaving group hardly affects the ratio of 1- and 2a-substituted products. This indicates that the alkylation might proceed by an electron transfer (SET) instead of an SN2 mechanism. Further evidence for SET was obtained by the use of free radical and electron scavengers. The substitution products 1-benzylacenaphthene and 2a-benzyl-2a,5-dihydroacenaphthylene could be isolated and purified.
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    13C-Labelled (±±)-Catechin From Potassium [13C]Cyanide (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1279-1283 
    Details
    ISSN: 1434-193X
    Keywords: Flavonoids ; Catechin ; Isotopic labeling ; Carbon 13 ; Total synthesis ; French paradox ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Racemic 4-[13C]catechin 14 has been synthesized in ten steps starting from potassium [13C]cyanide. The intermediate chalcone 9 was formed by acylation of the benzylated phloroglucinol 7 with the caffeic acid synthon 6, using the trifluoroacetic mixed anhydride. The flavonoid skeleton was then obtained by previously described reactions such as the reduction of chalcone 9 and dihydroxylation of flavene 11. Such [13C]-labelled polyphenols should prove to be useful tools for human biological investigations.
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    Synthesis of Highly Enantio-Enriched α-Amino Acids by Carboxylation of N-(α-Lithioalkyl)oxazolidinones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1297-1305 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Asymmetric synthesis ; Carboxylation ; N-(α-Lithioalkyl)oxazolidin-2-ones ; Isotopic labeling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -N-(α-Stannylalkyl)oxazolidinones can be obtained as a mixture of diastereomers in three steps from aldehydes with yields dependent on the R group of R-CHO. They can be transformed by a tin-lithium exchange to N-(α-lithioalkyl)oxazolidinones which equilibrate rapidly to one diastereomer. These compounds give rise, after carboxylation, to the diastereopure N-(α-carboxyalkyl)oxazolidinones. Transformation of the oxazolidinone moiety to a free amino group is accomplished by a Birch-type reduction. Using this method, L-methionine, L-alanine, L-leucine and L-homocysteine were obtained in good yields and ee = 92% to ≥ 95%. The short time required for the whole sequence makes this method ideal for synthesising 1-[11C]amino acids.
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    Synthesis of Diospyrin, a Potential Agent Against Leishmaniasis and Related Parasitic Protozoan Diseases (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1313-1317 
    Details
    ISSN: 1434-193X
    Keywords: Leishmaniasis ; Natural products ; Phytochemistry ; Quinones ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first synthesis of diospyrin [2,6′-bis(5-hydroxy-7-methyl-1,4-naphthoquinone), 1] was achieved by employing Suzuki coupling between 5 and 14 as the key reaction to connect the two 7-methyljuglone units.
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    Synthesis of Biaryl Compounds by Vinylogous Michael Reactions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1977-1982 
    Details
    ISSN: 1434-193X
    Keywords: Biaryls ; Homogeneous catalysis ; Iron ; Addition reactions ; Quinones ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Acceptor-substituted cycloalkenones 1 undergo an iron(III)-catalyzed vinylogous Michael reaction - a sequence of enone-dienol tautomerism, [4+2]-cycloaddition, and retro-aldol reaction - with quinone derivatives 3. A variety of products is obtained ranging from meta-terphenyl precursors 5 to dihydronaphthobenzofurans 7. Reaction of 1,2-naphthoquinone (3e) with vinylogous donors 1 yields cross-coupled products 12, which can be further converted into highly functionalized biaryl compounds 13 and 14.
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    Base- and Sugar-Modified Cytidine Monophosphate N-Acetylneuraminic Acid (CMP-Neu5Ac) Analogues - Synthesis and Studies with α(2-6)-Sialyltransferase from Rat Liver (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1467-1482 
    Details
    ISSN: 1434-193X
    Keywords: Glycosyl phosphates ; Nucleosidephosphate sugars ; Neuraminic acid ; Glycosyltransferase ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The reaction of sialyl phosphites 1, 22a-d, 28, 39, and 45 with acyl-protected riboside 5-phosphorous acids 2a,b and 23 directly furnished, without addition of a catalyst, under phosphite/phosphate exchange the corresponding β-configured sialyl riboside monophosphates 3a,b, 24a-d, 29, 46, and 47. The synthesis of the starting materials, formation of the products, and their treatment with sodium methanolate in methanol and subsequent hydrolysis of the sialic acid ester moiety to provide the unprotected target molecules 4a,b, 25a-d, 30, 48, and 49 is described. Investigations with α(2-6)-sialyltransferase from rat liver showed that base replacement in CMP-Neu5Ac (4a,b) is not tolerated by the enzyme but that modifications of the 5-, 8-, or 9-position of the neuraminic acid residue (25a-d, 30, 48, 49) are tolerated.
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    An Unprecedented CoII-Tetraphenylporphyrin-Catalyzed Decomposition of Bicyclic Endoperoxides: A New Approach to Substituted Furofuran Systems (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1359-1363 
    Details
    ISSN: 1434-193X
    Keywords: Endoperoxides ; Cycloheptatriene ; Dichloroketene ; Singlet oxygen ; Cobalt ; Porphyrins ; Furans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -CoII-tetraphenylporphyrin-catalyzed decomposition of bicyclic endoperoxides 4 and 5 with a strained double bond moiety has been studied. Compounds 4 and 5 have been synthesized by photooxygenation of 3 which itself was obtained by dichloroketene addition to cycloheptatriene, followed by removal of the chlorine atoms. An unusual decomposition mode of 4 promoted by CoII-TPP resulted in the formation of 8 and 9 which are important building blocks in furofuran systems.
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    Synthesis and Characterization of New Enantiopure 7,7′-Disubstituted 2,2′-Dihydroxy-1,1′-binaphthyls: Useful Ligands for the Asymmetric Allylation Reaction of Aldehydes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1375-1375 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -No Abstract.
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    Synthesis of 2-Fluoro Analogues of Frontalin (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1387-1389 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Epoxidations ; Asymmetric synthesis ; Fluorine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of enantiomerically and diastereomerically pure (-)-(1R,2R,5R)- and (-)-(1R,2S,5R)-2-fluoro frontalin (7) starting from (+)-(1S)-menthyl-(R)-toluene-4-sulfinate, methylmagnesium bromide, methyl fluoroacetate, 4-pentenyl bromide and diazomethane is described. The absolute stereochemistry was unambiguously determined by X-ray analysis of (+)-(1S,2R,5S,RS)-5, an intermediate in the synthesis of the enantiomeric (+)-(1S,2R,5S)-2-fluoro frontalin (7).
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    Synthesis of Allylic Isoprenoid Diphosphates by SN2 Displacement of Diethyl Phosphate (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1401-1410 
    Details
    ISSN: 1434-193X
    Keywords: Phosphorylations ; Deuterium labeling ; Asymmetric labeling ; Terpenoid biosynthesis ; Enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Allylic polyenyl diphosphates such as geranyl and (E,E,E)-geranylgeranyl diphosphates are ubiquitous substrates for monoterpene and diterpene synthases and transferases in isoprenoid biosynthesis. These enzyme substrates were prepared in asymmetrically labeled form by reduction of 1-deuterio aldehyde precursors with (R)- and (S)-Alpine boranes®, conversion into diethyl phosphates, and SN2 displacements with tris(tetrabutylammonium) pyrophosphate which occurred slowly with essentially complete inversion of configuration over 2-5 days. The 8α- and 8β-hydroxy-17-nor analogs (13 and 14) of copalyl diphosphate as well as the (15R)-deuterium-labeled form of 13 were similarly prepared from nor-diols 11, (15S)-[15-2H1]-11, and 12 by means of regioselective phosphorylation of the allylic hydroxy groups and displacements with pyrophosphate anion. The configurations and enantiopurities of the deuterium-labeled geraniols, before and after the SN2 displacements, and the diastereopurity of the bicyclic keto alcohol intermediate (15S)-[15-2H1]-15 were determined by conversion into (1S)-camphanate esters and 1H-NMR analysis. Amino alcohol 18 was similarly converted into amino diphosphate 19, 15-aza-14,15-dihydro GGPP, a potential aza analog inhibitor for diterpene synthases which generate stereoisomeric forms of copalyl diphosphate.
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