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  • 1995-1999  (33)
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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of natural products 58 (1995), S. 1543-1554 
    ISSN: 1520-6025
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of organic chemistry 60 (1995), S. 7891-7895 
    ISSN: 1520-6904
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 396-409 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The chloromercurate(II) salts of 2-, 3- and 4-chloropyridine display a variety of anion stoichiometries and structures, including the rare [Hg3Cl10]4− stoichiometry. 2-Chloropyridinium trichloromercurate(II), (I), (C5H5ClN)[HgCl3], monoclinic, P21/n, a = 9.094 (8), b = 18.143 (4), c = 12.902 (3) Å, β = 106.13 (4)° with Z = 8, has the [HgCl3]− stoichiometry, but the anions are infinite chains composed of [HgCl3]−, HgCl2 and Cl− moieties linked by longer Hg...Cl contacts. Hydrogen bonds link the cations to the formal Cl− ions. Tetrakis(3-chloropyridinium) decachlorotrimercurate(II), (II), (C5H5ClN)4[Hg3Cl10], monoclinic, P21/n, a = 7.522 (2), b = 28.046 (3), c = 9.165 (2) Å, β = 105.78 (2)° with Z = 2, has the rare [Hg3Cl10]4− stoichiometry and contains infinite one-dimensional double-stranded {([HgCl4]2−)2 [HgCl2]}n anionic chains made up of linear HgCl2 and distorted [HgCl4]2− entities linked together by longer Hg...Cl contacts. The HgCl2 moieties are joined by double [HgCl4]2− bridges. Hydrogen bonds link the cations to the sides of the anionic columns. Tetrakis(4-chloropyridinium) decachlorotrimercurate(II), (III), (C5H5ClN)4[Hg3Cl10], triclinic, P1¯, a = 9.907 (3), b = 13.226 (2), c = 7.282 (2) Å, α = 84.41 (2), β = 74.81 (2), γ = 87.34 (2)° with Z = 1, also has the [Hg3Cl10]4− stoichiometry and the same type of {([HgCl4]2−)2[HgCl2]}n anionic chains that were found in compound (II), but the formal HgCl2 and [HgCl4]2− moieties are more discrete with much weaker contacts linking the individual units. Bifurcated hydrogen bonds with the cations cross-link the anionic chains to form an infinite two-dimensional network. Second forms of the 3- and 4-chloropyridinium salts were also obtained. 3-Chloropyridinium trichloromercurate(II), (IV), (C5H5ClN)[HgCl3], monoclinic, P21/c, a = 7.243 (5), b = 22.145 (8), c = 12.320 (3) Å, β = 99.52 (3)° with Z = 8, has the [HgCl3]− stoichiometry, but the anions are infinite chains composed of distorted [Hg2Cl6]2− moieties. Bifurcated hydrogen bonds from the cations cross-link the anionic chains to form infinite two-dimensional layers. Bis(4-chloropyridinium) hexachlorodimercurate(II), (V), (C5H5ClN)2[Hg2Cl6], monoclinic, C2/m, a = 13.447 (3), b = 7.534 (2), c = 9.939 (2) Å, β = 97.48 (2)° with Z = 2, contains highly symmetrical discrete [Hg2Cl6]2−anions. Bifurcated hydrogen bonds from the cations interconnect the anions to form infinite one-dimensional chains.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Boron Trifluoride Catalyzed Reaction of 3-Amino-2H-azirines and Amides: Formation of 4,4-Disubstituted 4H-ImidazolesReaction of trifluoroacetamide and 3-amino-2H-azirines 1 in refluxing MeCN affords 4-amino-2-(trifluoromethyl)-4H-imidazoles 5 in fair yields (Scheme 3). Less acidic amides do not react with 1 under similar conditions. Therefore, a procedure involving BF3-catalysis has been elaborated: the aminoazirine 1 in CH2Cl2 at -78° is treated with BF3 · Et2O and then with a solution of the sodium salt of an amide in THF, prepared by addition of sodium hexamethyldisilazane at -78°. The 4H-imidazoles of type 5 are formed in ca. 50% yield (Scheme 4). Reaction mechanisms for this ring enlargement of 1 are proposed in Schemes 5 and 6.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: First Example of an H-Shift in ‘Thiocarbonyl Aminides’ (N-(Alkylidenesulfonio)aminides)Reaction of benzyl azide (15a) with the sterically hindered C=S group of 4,4-dimethyl-1,3-thiazole-5(4H)-thiones 14 (Scheme 3) and 1,1,3,3-tetramethylindane-2-thione (17, Scheme 4) at 80° leads to the corresponding imines in high yield, without formation of any by-product. In contrast, 15a and 2,2,4,4-tetramethyl-3-thioxocyclobutanone (7) under the same conditions yielded, in addition to imine 19, products 20a and 21 (Scheme 5). For the formation of 20a, a reaction mechanism via [1,4]-H shift in the intermediate ‘thiocarbonyl aminides’ 23 is proposed (Scheme 6). Product 21 as well as the dithiazole derivative 22, which is formed only in the reaction with 4-nitrobenzyl azide (15c), are formal adducts of the dipole 23. Whereas precedents are known for the formation of cycloadducts of type 22, the pathway to 21 is not known. Two possible mechanisms of its formation are proposed in Schemes 8 and 9.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The X-ray crystal structures of 9-phenylbenz[a]azulene (4) and the corresponding non-benzannelated form, 4-phenylazulene (5), have been determined (cf. Fig.2). In contrast to 5, the skeleton of which shows nearly equal C,C bond lengths (cf. Table 1), the seven-membered ring of 4 exhibits clearly alternating C,C bond lengths (cf. Table 1). This is in agreement with a strong accentuation of the heptafulvene substructure in 4 by the [a] benzannelation. The alternating bond lengths of 4 and of its parent structure 3 are also reflected in the corresponding variations of the 3J(H,H) and 1J(13C,13C) values of these benz[a]azulenes (cf. Tables 4 and 5). Computations on the MP2/6-31G* level as well as on the BP86/6-31G* level for azulene (6), benz[a]azulene (3), and heptafulvene (7) are in good agreement with the experimental values (cf. Tables 6-8).
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 855-874 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,5-Dipolar Electrocyclization of Acyl-Substituted ‘Thiocarbonyl-ylides’ to 1,3-OxathiolesThe reaction of α-diazoketones 15a, b with 4,4-disubstituted 1,3-thiazole-5(4H)-thiones 6 (Scheme 3), adamantanethione (17), 2,2,4,4-tetramethyl-3-thioxocyclobutanone (19; Scheme 4), and thiobenzophenone (22; Scheme 5), respectively, at 50-90° gave the corresponding 1,3-oxathiole derivatives as the sole products in high yields. This reaction opens a convenient access to this type of five-membered heterocycles. The structures of three of the products, namely 16c, 16f, and 20b, were established by X-ray crystallography. The key-step of the proposed reaction mechanism is a 1,5-dipolar electrocyclization of an acyl-substituted ‘thiocarbonyl-ylide’ (cf. Scheme 6). The analogous reaction of 15a, b with 9H-xanthen-9-thione (24a) and 9H-thioxanthen-9-thione (24b) yielded α,β-unsaturated ketones of type 25 (Scheme 5). The structures of 25a and 25c were also established by X-ray crystallography. The formation of 25 proceeds via a 1,3-dipolar electrocyclization to a thiirane intermediate (Scheme 6) and desulfurization. From the reaction of 15a with 24b in THF at 50°, the intermediate 26 (Scheme 5) was isolated. In the crude mixtures of the reactions of 15a with 17 and 19, a minor product containing a CHO group was observed by IR and NMR spectroscopy. In the case of 19, this side product could be isolated and was characterized by X-ray crystallography to be 21 (Scheme 4). It was shown that 21 is formed - in relatively low yield - from 20a. Formally, the transformation is an oxidative cleavage of the C=C bond, but the reaction mechanism is still not known.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 213-219 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of enolates of α-unsubstituted carboxamides 3 with diphenyl phosphorazidate (DPPA) and di(tert-butyl) dicarbonate (‘Boc anhydride’) in THF at -78° yielded 2-{[(tert-butoxy)carbonyl]amino}carboxamides 5 (Scheme 2) which are derivatives of α-amino acids. In this reaction, DPPA acts as an electrophilic amination reagent. A reaction mechanism is proposed in Scheme 3.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1121-1128 
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of 3-(dimethylamino)-2,2-dimethyl-2H-azirine (1a) with 4,5-dihydro-7,8-dimethoxy-1,2-benzothiazepin-3-one 1,1-dioxide (4) in dioxane at room temperature gave the correspondingly substituted 4H-1,2,5-benzothiadiazecin-6-one 1,1-dioxide 5a in 64% yield (Scheme 2). The structure of this novel ten-membered ring-enlargement product was established by X-ray crystallography (Fig.). Under more vigorous conditions (refluxing dichloroethane), 5a was formed together with the isomeric 6a, both in low yield. The 3-(dimethylamino)-2H-azirines 1b and 1c reacted sluggishly to give the two isomeric ring-enlargement products of type 5 and 6 in yields of 24-29% and 2-4%, respectively (Table 1). Even less reactive is 2,2-dimethyl-3-(N-methyl-N-phenylamino)-2H-azirine (1d), which reacted with 4 in MeCN only at 65°. Under these conditions, besides numerous decomposition products, only traces of 5d and 6d were formed. No ring enlargement was observed with the sterically crowded 1e, which bears an isopropyl group at C(2).
    Additional Material: 1 Ill.
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  • 10
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ring Opening of Sterically Crowded Spirocyclic 2, 5-Dihydro-l, 3, 4-thiadiazoles by Cycloaliphatic Secondary AminesAt room temperature, the spirocyclic 2, 5-dihydro-l, 3, 4-thiadiazole 3 reacted with cyclic secondary amines 6 via ring opening to give N-alkylidene-hydrazones of type 7 (Scheme 2). A reaction mechanism via a base-catalyzed transformation of the dihydrothiadiazole ring to the corresponding thiolate 19 and the intermediate thioaldehyde 21 is proposed in Scheme 6. An analogous reaction occurred with the mixture of the dispiro compounds 4/5 and morpholine (6a) or azetidine (6d), leading to a mixture of isomeric dihydrazones 8 and 9 (Scheme 3). The structure of the symmetrical isomer 8a was established by X-ray crystallography. In addition to 8a and 9a, the thiirane lOa (Scheme 3) was isolated as a minor product.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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