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  • Natural products  (10)
  • Rearrangements  (9)
  • Wiley-Blackwell  (18)
  • Blackwell Publishing Ltd
  • Elsevier
  • 2000-2004  (18)
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  • Wiley-Blackwell  (18)
  • Blackwell Publishing Ltd
  • Elsevier
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Year
  • 1
    Electronic Resource
    Electronic Resource
    A New Route to 2,7- and 7-Functionalized Labdanes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1609-1615 
    Details
    ISSN: 1434-193X
    Keywords: Terpenoids ; Natural products ; Total synthesis ; Cyclizations ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new route for the synthesis of 2,7- and 7-functionalized labdanes starts from (R)-carvone (1). 11-Nordrim-7-en-9-one (15) is an appropriate starting material for the total synthesis of hispanone (21), a biologically active furolabdane isolated from the Mediterranean medicinal plant Ballota saxatilis.
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation of Kingiside from Aucubin (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1623-1626 
    Details
    ISSN: 1434-193X
    Keywords: Iridoid glucoside ; (8S)-Kingiside ; (8S)-Loganin ; (8S)-7-Ketologanin ; Asymmetric synthesis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetraacetyl derivative 8 of the naturally occurring kingiside (8a) was prepared from aucubin (1). Intermediates in the synthesis were (8S)-tetraacetyl loganin (6) and (8S)-tetraacetyl-7-ketologanin (7), whose free (8R)-epimers occur in many different plants (Caprifoliaceae, Loganiaceae). The 13C NMR spectrum allows the structure to be unequivocally identified.
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  • 3
    Electronic Resource
    Electronic Resource
    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.
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of Ascididemine and an Isomer (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 849-855 
    Details
    ISSN: 1434-193X
    Keywords: Marine alkaloids ; Heterocycles ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ascididemine (9H-quino[4,3,2-de][1,10]phenanthrolin-9-one) (1) and an isomer (9H-quino[4,3,2-de][1,7]phenanthrolin-9-one) (4) have been synthesized starting from 1,4-dimethoxyacridone (7). The acridone was converted into 1,4-dimethoxy-9-ethynylacridine (11) by a triflate coupling. The ethynylacridine was converted in one-pot into 3H-6-methoxypyrido[2,3,4-kl]acridine (15) by reaction with sodium diformylamide; the mechanism of this key transformation is discussed. Conversion into 6H-4-bromopyrido[2,3,4-kl]acridin-6-one (19) and 6H-pyrido[2,3,4-kl]acridin-6-one (17), followed by reaction of each of these under high pressure conditions with acrolein N,N-dimethylhydrazone, gave ascididemine and its isomer, respectively.
    Additional Material: 2 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Stereodivergent Synthesis of Highly Substituted Tetrahydropyrans (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 73-82 
    Details
    ISSN: 1434-193X
    Keywords: Natural products ; Oxa-conjugate addition ; Rearrangement ; Tetrahydropyrans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Intramolecular oxa-conjugate addition has been employed in a stereoselective synthesis of enantiopure polyalkyl-substituted tetrahydropyrans, which are frequently found as substructures in many natural products. The requisite cyclization precursors, 7-hydroxy-2-enimides 3 and 7-hydroxy-2-enoates 6 were easily accessible by silyloxy Cope rearrangements of the appropriate chiral syn-aldols. It was found that the stereoselectivity of the cyclization could be controlled by judicious choice of the carboxylic acid derivative, resulting in a kinetically controlled reaction for the imides and a thermodynamically controlled process for the esters. Mechanistic considerations that could account for the stereocontrol of the process are outlined.
    Additional Material: 3 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Structural and Biosynthetic Investigations of the Rubromycins (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 729-735 
    Details
    ISSN: 1434-193X
    Keywords: Rubromycins ; Natural products ; Biosynthesis ; Quinones ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The structure of the known secondary metabolite β-rubromycin was corrected, based on spectroscopic and chemical investigations, from o-quinone 1 to p-quinone 6. By feeding [U-13C3]malonic acid to the rubromycin-producing strain, Streptomyces sp. A1, the polyketide origin of the skeleton was verified, but the identity of the starter unit and the folding mechanism of the polyketide chain are still unclear. From the culture broth of the strain A1, in addition to 6, the co-metabolites γ-rubromycin (3), δ-rubromycin (4) and 3′-hydroxy-β-rubromycin (7) were isolated. Their structures were determined or confirmed by detailed spectroscopic analysis. The rubromycins inhibit HIV-1 reverse transcriptase (RT) and are cytostatically active against different tumor cell lines.
    Additional Material: 1 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    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).
    Additional Material: 2 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    A New Analogue of Yessotoxin, Carboxyyessotoxin, Isolated from Adriatic Sea Mussels (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 291-295 
    Details
    ISSN: 1434-193X
    Keywords: Diarrhetic Shellfish Poisoning ; NMR spectroscopy ; Yessotoxin ; Natural products ; Carboxyyessotoxin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new analogue of yessotoxin (YTX), carboxyYTX, 3, was isolated from the digestive glands of mussels cultured on the Italian Adriatic coast. Its structure was determined by MS and NMR spectroscopy.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis of 5-Methylbenzo[b]thieno[2,3-c]isoquinolines and5-Methylbenzo[b]seleno[2,3-c]isoquinolines (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1353-1357 
    Details
    ISSN: 1434-193X
    Keywords: Heterocycles ; Rearrangements ; C-C coupling ; C-C coupling ; Cyclizations ; Isoquinolines ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -5-Methylbenzo[b]thieno[2,3-c]isoquinolines and 5-methylbenzo[b]seleno[2,3-c]isoquinolines 11b,c have been prepared by Bischler-Napieralski cyclization of 2-acetamido-3-phenylbenzo[b]heteroarenes.
    Additional Material: 4 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    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.
    Additional Material: 1 Tab.
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  • 11
    Electronic Resource
    Electronic Resource
    Modifications of Peptides by Chelate Claisen Rearrangements of Manganese Enolates (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1241-1251 
    Details
    ISSN: 1434-193X
    Keywords: Amino acids ; Enolates ; Rearrangements ; Metal complexes ; Peptides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Deprotonation of allylic esters of peptides at -70 °C in the presence of metal salts results in the formation of metal peptide enolate complexes, which undergo Claisen rearrangement on warming to room temperature to produce stereoselectively modified peptides. By far the best results are obtained with manganese enolates. With these enolates, the amino acids incorporated in the peptide chain have no significant influence on the rearrangement, neither on the yield nor on the stereochemical outcome. Therefore, this protocol is extremely suitable for the stereoselective modification of peptides by using esters of chiral allylic alcohols. α-Alkylated amino acids can be incorporated into peptides as well.
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  • 12
    Electronic Resource
    Electronic Resource
    Reactions of Pyridine Analogues of Aza-ortho-xylylenes Generated from 1,3-Dialkylpyridosultams (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1263-1270 
    Details
    ISSN: 1434-193X
    Keywords: Alkenes ; Nitrogen heterocycles ; Pericyclic reactions ; Rearrangements ; Spiro compounds ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -2,3-Dihydro-3-imino-2-methylenepyridines, generated by thermal extrusion of SO2 from 1,3-dialkyl-1,3-dihydroisothiazolo[4,3-b]pyridine 2,2-dioxides (1,3-dialkylpyridosultams), underwent [1,5] hydrogen shifts, which led to 3-alkylamino-2-vinylpyridine derivatives. Cycloalkanespiro-3-pyridosultams 12, which were easily obtained by alkylation of pyridosultams with α,ω-dihaloalkanes, gave, in a similar reaction, 3-alkylamino-2-cycloalkenylpyridine derivatives 14 in good yields. Cyclobutanespiro-3-pyridosultam 12b, after thermal extrusion of SO2, formed cyclobutenyl derivative 14b, which underwent a ring-opening reaction to form butadiene derivative 15. The latter can be trapped with dienophiles, for example, N-phenylmaleimide.
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  • 13
    Electronic Resource
    Electronic Resource
    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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  • 14
    Electronic Resource
    Electronic Resource
    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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  • 15
    Electronic Resource
    Electronic Resource
    Cyclohexa-1,2,4-triene from 1-Bromocyclohexa-1,4-diene (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1871-1874 
    Details
    ISSN: 1434-193X
    Keywords: Cycloallenes ; Cycloadditions ; Eliminations ; Strained molecules ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---1-Bromocyclohexa-1,4-diene (3) was prepared from trans-4,5-dibromocyclohexene by elimination of hydrogen bromide. Treatment of a solution of 3 in furan or 2,5-dimethylfuran with KOtBu afforded the tetrahydroepoxynaphthalenes 4 and 5, respectively. The structure of these products is evidence for the title cycloallene (isobenzene 1) being the reactive intermediate. The compounds 4 and 5 were dehydrogenated by DDQ to the known dihydroepoxynaphthalenes 6 and 7, respectively. These conversions unambiguously confirm the structures of 4 and 5. In pure styrene, 3 was not attacked by KOtBu, and only upon the addition of 18-crown-6 did a reaction occur. This reaction did not, however, furnish the known [2+2] cycloadduct 9 of styrene and 1, but, instead, a small amount of 1,2-diphenylethane (8) was formed. In agreement with this finding, the conjecture that 1 was deprotonated to give the phenyl anion was confirmed by the treatment of a solution of 3 and benzophenone in THF with KOtBu, which resulted in the formation of triphenylmethanol.
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  • 16
    Electronic Resource
    Electronic Resource
    Total Syntheses of Squamocin A and Squamocin D, Bi-tetrahydrofuran Acetogenins from Annonaceae (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1889-1904 
    Details
    ISSN: 1434-193X
    Keywords: Total synthesis ; Natural products ; Squamocin A ; Squamocin D ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The total syntheses of the Annonaceous acetogenins squamocin A and squamocin D have been achieved. The synthesis follows a modular strategy, wherein a left-side chain, the central bis-THF core and the right-side chain are assembled together. Key reactions are additions of organomagnesium compounds to bi-THF aldehydes. At the end of the synthesis the butenolide moiety was introduced. This modular synthetic approach should be useful for the synthesis of other related natural products as well as pharmacologically interesting analogs.
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  • 17
    Electronic Resource
    Electronic Resource
    Solid-Acid Catalysed Rearrangement of Cyclic α,β-Epoxy Ketones (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1905-1911 
    Details
    ISSN: 1434-193X
    Keywords: α,β-Epoxy ketones ; Rearrangements ; Zeolites ; Clays ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Various cyclic α,β-epoxy ketones rearranged to α-formyl ketones and/or vic-diones in the presence of catalytic amounts of zeolites and montmorillonite K10. This provides an excellent alternative to conventional homogeneous systems with respect to yields and workup. Differences in product distribution and type of products in the rearrangement of pulegone oxide could be reasonably explained by invoking different pathways for homogeneous and heterogeneous catalysts.
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  • 18
    Electronic Resource
    Electronic Resource
    Claisen Rearrangement of Allyl Bromofluorovinyl Ethers (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1933-1937 
    Details
    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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