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  • 1
    ISSN: 1434-193X
    Keywords: Liquid crystals ; Discotic twins ; Discotic oligomers ; Spiro compounds ; Triphenylene ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The novel spiro-twins 3a-f were prepared in three steps by one-pot oxidative coupling of guaiacol (9) and 1,2-dialkoxybenzenes 10a-f, followed by demethylation of the triphenylene 11 and subsequent etherification with the tetrabromide 6. A related strategy gave the tetramers 7a-f in two steps. Whereas derivatives 3a,b and 7a,b with pentyloxy and hexyloxy chains showed isotropic melting behavior, compounds 3c-f and 7c-f with longer alkyl chains displayed columnar mesophases. DSC, polarizing microscopy, X-ray diffraction and molecular modeling studies were used to further characterize the type of mesophase. For the spiro-twin 3 either a rectangular or a hexagonal columnar phase were conceivable. In case of 7f a hexagonal columnar mesophase was assigned.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    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.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-1948
    Keywords: Pyridine N-oxide ; Pyridine ; Asymmetric catalysis ; Amino acids ; Amino alcohols ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Starting from picolinic acids 3 and 4, the amino acid-derived 2-aminoacylpyridine N-oxides 1a,c-e and 2,6-bis(aminoacyl)pyridine N-oxides 2b-e can be prepared in two steps by the coupling of picolinic acid N-oxides 5 and 6 under Appel conditions with the corresponding L-amino acid ester or (1R,2S)-norephedrine. Compounds 1 and 2 were used as chiral ligands in two different asymmetric catalyses. In the catalytic addition of diethylzinc to benzaldehyde 11, low enantioselectivities (2-29% ee) were obtained regardless of the amino acid moiety. However, the corresponding 2,6-bis(aminoacyl)pyridines 7 and 8 led to increased ee values (55% ee). In the catalytic reduction of ketones 9a-c to alcohols 10a-c low enantioselectivities were observed for alanine-, valine-, and leucine-derived N-oxides 1a,c and 2b,c. An increase of selectivity was observed for bis-methionine ligand 2d (32-38% ee) relative to that of mono-methionine ligand 1d (7-16% ee). However, mono-norephedrine ligand 1e (≤ 64% ee) and the corresponding bis-norephedrine ligand 2e (≤ 51% ee) displayed the highest selectivities. The influence of the N-oxide moiety on the enantioselectivity was demonstrated by the observation that 2,6-bis(aminoacyl)pyridines 7 and 8 gave much lower selectivities than the corresponding pyridine N-oxides 2d and e.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: 3-Hydroxyisoxazoles ; Alkylation ; Protecting groups ; Muscimol ; GABA analogues ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regioselectivity of the 3-hydroxyisoxazole-5-ester 1 is studied with respect to O- versus N-alkylation. 3-O-Alkyl products 2 are highly favoured with benzyl, benzhydryl, and allyl bromide (≥ 91:9), in contrast to known uses of 5-alkyl-3-hydroxyisoxazoles or when methylation with diazomethane (or methyl iodide) is effected. Methoxymethylation leads to the N-substituted isoxazolinone 3e only. On reduction with DIBAH, the esters 2 afford 3-O-protected 3-hydroxyisoxazole-5-carbaldehydes 4 (75-98%). For removal of the benzyl protecting groups, three variations (HBr/HOAc, H2-Pd/BaSO4, NBS/AIBN) were found useful with 5-ester, 5-formyl, and 5-hydroxymethyl derivatives. The free 3-hydroxy-5-carbaldehyde 9, the putative toxic metabolite of the GABA agonist muscimol, is prepared accordingly. The O-protected 3-hydroxyisoxazole-5-carbaldehydes 4 constitute versatile intermediates in various routes to analogues of CNS-active amino acids and can now be obtained in a highly efficient manner.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-193X
    Keywords: Indolizino[3,4-b]quinoline ; Receptors ; Molecular tweezers ; Tentacle molecules ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A convenient diastereoselective synthetic route to the molecular tweezer bis(indolizino[3,4-b]quinolyl)methane 9 and the rigid indolizino[7′,8′:2,3]quinolino[8,7-h]indolizino[8,7-b]quinolines 14, 15 as potential receptor molecules has been developed, involving double imine condensation followed by Lewis acid catalyzed biscyclization of prolinal-derived bis(imines) 8 and 13, respectively. Whereas the use of SnCl4 leads to the formation of the planar polycycle 15, the corresponding concave product 14 is formed in the presence of EtAlCl2. Both compounds 14, 15, as well as tweezer 9 have been characterized by X-ray crystal-structure analysis. Although tris(imines) 20, 24 derived from 1,3,5-triaminobenzene (18) and tris(4-aminophenyl)amine (23) could be obtained similarly by molecular sieve-catalyzed condensation, the corresponding triscyclization could not be achieved. However, by attaching preformed indolizino[3,4-b]quinoline subunits 25 and 31 to an aromatic core, the bidentate receptors 30, 33 and the tentacle molecule 28 were accessible.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 7-Methyloctahydroacridines 7a-d were obtained by a one-pot imine condensation/Lewis acid-catalyzed cyclization from aniline derivatives 5a-d and aldehyde 6. Only those compounds 7 could be oxidized with DDQ to the corresponding octahydroacridine-7-carbaldehydes 9, which bear a meta-chloro or bromo substituent (with respect to the methyl group) in addition to the para-amino group (i.e. 7c,d → 9c,d). Aldehyde 9c was further converted to the novel tripodand 11 which was characterized by X-ray crystal structure analysis.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 985-993 
    ISSN: 0947-3440
    Keywords: Chelation control ; Lewis acid catalysis ; Hetero Diels-Alder reactions ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lewis acid-catalyzed cyclization of proline-derived N-arylimines 8 gives the tetracyclic decahydro-7,7,11-trimethyl-in-dolizino[3,4-b]quinolines 17a, b in a ratio, which is highly dependent on the coordination number of the acidic catalyst. Whereas monodentate Brønsted and Lewis acids as well as octahedral bidentate Lewis acids preferably gave the all-trans product 17b, the all-cis product 17a was obtained by tetrahedral aluminium Lewis acids. In contrast to this chelation-controlled reversal of diastereoselectivity, mixtures of cis/trans undecahydro-6,6,10-trimethyl-11-azacyclopenta[a]-anthracenes 18b-e, h were isolated from the cyclization of the corresponding cyclopentane-derived N-arylimines 16 irrespective of the Lewis acid. Force field calculations support a stepwise iminium ion cyclization under thermodynamic control rather than a concerted hetero-Diels-Alder mechanism.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0947-3440
    Keywords: Ene reaction ; Benzo[b]quinolidines ; Azepino[1,2-b]isoquinolines ; Lewis acid catalysis ; Nitrogen heterocycles ; Cyclizations ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (L)-Phenylalanine 4 can be converted to N-(4-methyl-3-pentenyl)tetrahydrosisoquinoline-3-carbaldehyde 10 and the corresponding homologous aldehyde 19 in 4 and 5 steps, respectively, by employing the Pictet-Spengler reaction as the key step. After Lewis acid catalyzed cyclization of 10 and 19 the cis-configured 1-hydroxybenzo[b]quinolizidine 21a and 11-hydroxyazepino[1,2-b]isoquinoline 22a were obtained with high diastereoselectivities. Compound 21a, which was characterized by X-ray structure analysis, displays a fishbone pattern of endless zig-zag chains connected via intermolecular hydrogen bonds in the solid state.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1-11 
    ISSN: 0947-3440
    Keywords: Nitrogen heterocycles ; Imines ; Hetero-Diels-Alder reaction ; Hetero-ene reaction ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Novel Lewis acid-catalyzed cyclizations of N-arylimines and N-benzylimines derived from amino acids and terpenes allow the diastereoselective preparation of octahydroacridines, indolizino[3,4-b]quinolines, indolizidines, quinolizidines and piperidines. Although these two types of reactions can be classified as formal hetero-Diels-Alder and hetero-ene reactions respectively, both proceed stepwise via cationic intermediates, which allow stereochemical control via chelate complexes. Stereochemical and mechanistical studies are described briefly.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0947-3440
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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