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  • 1,3-Disilacyclobutanes  (2)
  • Carbohydrates  (2)
  • Bis(methylthio)maleonitrile  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Controlled Conversion of the Transient 2-Mesityl-1,1-bis(trimethylsilyl)silene into a Tetrahydro-2,3-disilanaphthalene, a 1,2-Disilacyclobutane, or a 1,3-Disilacyclobutane (1995)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 128 (1995), S. 1083-1088 
    Details
    ISSN: 0009-2940
    Keywords: Silenes ; Silene dimerization ; 1,2-Disilacyclobutanes ; 1,3-Disilacyclobutanes ; 2,3-Disilanaphthalene, tetrahydro- ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mesityl[tris(trimethylsilyl)silyl]methanol (1) reacts with strong bases with elimination of trimethylsilanolate according to a Peterson-type mechanism, the outcome of the reaction being dependent on solvent, temperature, and nature of the organometallic base applied. Thus, 1 was converted by treatment with MeLi in ether at -78°C to (E)-1,2,3,8a-tetra -hydro-1-mesityl-5,7,8a-trimethyl-2,2,3,3-tetrakis (trimethylsi-lyl)-2,3-disilanaphthalene (3), formally a [2 + 4] cyclodimer of the transient silene (Me3Si)2Si=CHMes (2). The reaction of 1 with PhMgBr in THF after some days resulted in the formation of (Z)-3,4-dimesityl-1,1,2,2-tetrakis(trimethylsilyl) -1,2-disilacyclobutane (6) as the main product besides small quantities of 3, the polysilane (Me3SiSi(SiMe3)2CH2Mes (10), and the alkoxysilane (Me3Si)3SiCH(Mes)OSi(Si-Me3)2CH2Mes (7). Compound 6, the formal [2 + 2] cycloadduct of 2, can also be obtained by thermal treatment of 3 and is considered to be the thermodynamically more stable silene dimer whereas 3 is the kinetically preferred product. At high LiBr concentrations in the reaction mixture 1 was converted by PhMgBr in THF to (E)-2,4-dimesityl-1,1,3,3-tetrakis(tri- methylsilyl)-1,3-disilacyclobutane (13) besides 6 and [bis(tri-methylsilyl)silyl]mesityl(trimethylsiloxy)methane (11). The unforeseen formation of 13 is discussed as proceeding via the silene-lithium bromide adduct (Me3Si)2Si(Br)CH(Li)Mes (12). In the absence of LiBr 1 was converted by MeLi in THF at -78°C to 11 and the trisilane (Me3Si)2Si(Me)CH2Mes (4b). Probable pathways of the formation of all new compounds are discussed. For 6 and 13 the results of the X-ray structural analyses are given.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19951281105
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  • 2
    Electronic Resource
    Electronic Resource
    Silver(I) Sandwich Complexes of Oxa-Crowned Derivatives of Dithiomaleonitrile (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 807-814 
    Details
    ISSN: 0009-2940
    Keywords: Silver(I) sandwich complexes ; Crown dithioethers, unsaturated ; Bis(methylthio)maleonitrile ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination chemistry of the four oxa-crowned derivatives of dithiomaleonitrile mn-12S2O2, mn-15S2O3, mn-18S2O4, and mn-21S2O5 as well as of the acyclic bis(methylthio)maleonitrile mn-S2 with AgI was investigated by X ray structural and spectroscopic methods. The 2:1 complexes (ligand/AgI) [Ag(mn-12S2O2)2]PF6, [1]PF6, [Ag(mn-15S2O3)2]PF6, [2]PF6, and [Ag(mn-S2)2]PF6, [6]PF6, and the 1:1 complexes [Ag(mn-15S2O3)]ClO4, [3]ClO4, [Ag(mn-18S2O4)]PF6, [4]PF6, and [Ag(mn-21S2O5)]PF6 [5]PF6, were obtained with AgPF6 or AgClO4 in MeOH. The stoichiometry of the macrocyclic AgI complexes and the coordination mode of mn-S2On+1 coronands (n = 1-4) is determined by the length of the macrocyclic oligoethylene chain. - The mn-crown dithioethers mn-12S2O2 and mn-15S2O3 form with AgPF6 the new sandwich complexes [Ag(mn-12S2O2)2]PF6, [1]PF6, and [Ag(mn-15S2O3)2]PF6, [2]PF6. [1]PF6 crystallises in the triclinic space group P1. In the centrosymmetric cation [1]+ each mn-12S2O2 ligand is coordinated to the AgI centre in an endo manner via both S atoms and one O atom. The distance of the second O atom of mn-12S2O2 to AgI is somewhat longer than a normal Ag-Oether bond. The overall environment around AgI in [1]+ is that of a distorted cubic S4O4 set of donors. [2]PF6 crystallises in the monoclinic space group C2/c. In the centrosymmetric cation [2]+ silver(I) is planar-coordinated by the four S atoms of both mn-15S2O3 molecules. The six O atoms of both mn-15S2O3 ligands show only long-range interactions to the AgI ion. They surround AgI almost vertically to the planar S4 set of donors in a crown-like manner. - The crystal structures of the 1:1 complexes [Ag(mn-18S2O4)]PF6, [4]PF6, and [Ag(mn-21S2O5)]PF6, [5]PF6, consist of linear chain polymers. [5]PF6 forms an N-bridged chain polymer of endocyclic [Ag(mn-21S2O5)]+ units with S1O4NNitrile coordination at the AgI centre. In the 2:1 complex [Ag(mn-S2)2]PF6, [6]PF6, each mn-S2 acts as a monodentate NNitrile donor. - 13C-NMR studies in nitromethane solution confirm that the AgI ions in the complexes of the mn-crown dithioethers remain coordinated. However, the AgI ion in complex of mn-S2 is decoordinated.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961290711
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  • 3
    Electronic Resource
    Electronic Resource
    Head-to-Head versus Head-to-Tail Dimerizations of Transient Silenes - The Solvent-Dependent Regiospecifity of the Dimerization of 2-(2-Methoxyphenyl)-1,1-bis(trimethylsilyl)silene (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1667-1672 
    Details
    ISSN: 1434-1948
    Keywords: Silicon ; Silenes ; 1,2-Disilacyclobutanes ; 1,3-Disilacyclobutanes ; Eliminations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The regiospecifity of the dimerization of the transient 2-(2-methoxyphenyl)-1,1-bis(trimethylsilyl)silene (6), synthesized by base-initiated trimethylsilanolate elimination from (2-methoxyphenyl)[tris(trimethylsilyl)silyl]methanol (5) according to a modified Peterson mechanism, decisively depends on the donating ability of the solvent in which the silene is generated. In ether, 6 undergoes a formal [2 + 2] dimerization to afford 3,4-bis(2-methoxyphenyl)-1,1,2,2-tetrakis(trimethylsilyl)-1,2-disilacyclobutane (12), whereas in toluene the head-to-tail [2 + 2] cyclodimer, 2,4-bis(2-methoxyphenyl)-1,1,3,3-tetrakis(trimethylsilyl)-1,3-disilacyclobutane (13) was obtained. 1,1-Bis(trimethylsilyl)-2-(2,4,6-trimethoxyphenyl)silene (18), similarly made by a modified Peterson reaction, under the same conditions reacted with the eliminated trimethylsilanolate with readdition at the polar Si=C bond to give, after hydrolysis, 2-(2,4,6-trimethoxybenzyl)-1,1,1,3,3,3-hexamethyl-2-(trimethylsiloxy)trisilane (19). A possible mechanism explaining the solvent-dependent regiospecificity of the dimerization of 6 is discussed. The structures of 12 and 13 were determined on the basis of NMR and MS data as well as X-ray structural analyses.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Non-Classical Epimerisation of (1S,2S,3S,4R,5R)-1-O-Methylcyclohexane-1,2,3,4,5-pentol (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1259-1263 
    Details
    ISSN: 1434-193X
    Keywords: Inositols ; Epimerisation ; Acetals ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Methoxycyclitol 4 was acetalized in a non-classical one-pot procedure with chloral/dicyclohexylcarbodiimide forming the 4-epi derivative 6. The stepwise deprotection of compound 6 is also described. Thus, decarbamoylation to the acetal 7 was achieved by heating 6 with methanolic sodium methoxide, and cleavage of the acid-stable trichloroethylidene moiety was realised in two steps via the corresponding ethylidene acetals 8 and 9; the ethylidene function was removed with aqueous trifluoroacetic acid (compound 10 from 6 via 9). Finally, the carbamoyl derivative 10 was converted into the tetra-O-acetyl product 12 via the tetrol 11.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    A New Method for the Selective Introduction of Difluoromethyl and Trifluoromethyl Groups into Sugar Moieties (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 919-923 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Glycals ; Difluoromethylation ; Trifluoromethylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have studied the fluoroalkylation of the glucal 1 and the galactal 4 with dibromodifluoromethane via the 2-C-bromodifluoromethyl-substituted glycosyl bromides 2 and 5, respectively, followed by glycosylation to the methyl β-D-glycosides 3 and 6. The bromodifluoromethyl groups in the 2 position of the compounds 3 and 6 were converted into difluoromethyl and trifluoromethyl groups, respectively, giving the fluorinated monosaccharides 7-10.
    Type of Medium: Electronic Resource
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