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  • Kinetic d2-versus thermodynamic d4-reactivity of Li dienolates  (1)
  • NMR spectra  (1)
  • 1
    ISSN: 0170-2041
    Keywords: Amino acids, dehydro-, chiral ; Amino acids, nonproteinogenic ; Michael additions of cuprates ; a5-Reactivity of doubly unsaturated carbonyl compounds ; Kinetic d2-versus thermodynamic d4-reactivity of Li dienolates ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Stereoselective Conversions of t-Butyl rac-, (R)-, or (S)-5-Alkylidene-2-t-butyl-3-methyl-4-oxo-1-imidazolidinecarboxylates (Chiral 2,3-Dehydroamino Acid Derivatives) and Preparation of Some Nonproteinogenic Amino AcidsThe reacivity of the alkylidene derivatives 1-11 specified in the title and prepared in two operational steps from commercially available Boc-BMI and aldehydes is investigated. - According to high-field 1H-NMR analysis of the crude products, additions of H—H and D—D (catalytic hydrogenation, products 12-20, of R—H (BF3-activated R2CuLi/LiI and protonation, products 21-29), and of Cl2C (CHCl3/NaOH, products 33, 34) occur with complete selectivity from the face opposite to the t-butyl group. The doubly unsaturated carbonyl derivative 11 reacts with dibutyl cuprate in the δ position, again with formation of a single diastereomer 32, while trifluoroethylidene-Boc-BMI 3a is reduced to the difluoro analogue 30 by this cuprate. - Li dienolates are generated by deprotonation with LDA of the ethylidene (2a) and butylidene compound 4a; subsequent alkylations (with primary and secondary halides, products 35-41) and hydroxyalkylations (with aldehydes, products 42-44) lead to single products of electrophilic attack in the a carbonyl position (C-5 of the imidazolidinone ring) under kinetic control. On the other hand, reaction of the 2a-derived dienolate with benzaldehyde under equilibrating conditions furnishes the four possible (E/R, E/S, Z/R, and Z/S) γ adducts 45-48. - A combination of methods - 1H- and 13C-NMR spectroscopy, NOE measurements, spectroscopic analogies, chemical correlation (with authentic samples or by spectroscopic or optical comparison), and X-ray analysis (Table 1, Figure 1, Schemes 1 and 2) - is used to assign the product configurations and thus the stereochemical course of the reactions. Some unusual amino acids (50-52, 54, 55) are prepared by hydrolysis of the corresponding imidazolidinones.
    Additional Material: 2 Ill.
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  • 2
    ISSN: 0044-2313
    Keywords: 1,1,3,3-tetrachlorodisilazane ; silicon coordination compounds ; IR-spectra ; Raman spectra ; NMR spectra ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: 1,1,3,3-TetrachlorodisilazaneThe new compound 1 can be prepared by the reaction of calciumoctamminedichloride, CaCl2(NH3)8, with trichlorosilane, HSiCl3. IR, Raman, 1H and 29Si NMR spectra show a planar Si2NH framework, probably C2-symmetry of the whole molecule and a symmetrical distribution of the four chlorine atoms.In 1 we have got a compound with Bronsted and Lewis acidity, which reacts with three equivalents of pyridine to HSiCl2(py)2—NH(py)—HSiCl2. This addition compound exhibits a fourfold and a sixfold coordinated silicon atom as is shown by a 29Si-solid-NMR spectrum. By thermal decomposition of 1 the new compound 1,3,5-trichloro-2,4,6-tris(dichlorosilyl)-cyclo-1,3,5-trisil-2,4,6-triazane, Si6Cl9H6N3, 4, is formed. With piperidine, 1 reacts by substitution of all four chlorine atoms to compound 5, whereas with diazomethane the NH-functionality is converted to a NCH3 group in 6. Attempts of lithiation lead mainly to a substitution of the chlorine atoms by alkyl groups
    Notes: Durch Umsetzung von Calciumoktammindichlorid, CaCl2(NH3)8, mit Trichlorsilan, HSiCl3, kann die bisher unbekannte Verbindung 1,1,3,3-Tetrachlordisilazan, 1, Si2Cl4H3N, erhalten werden. IR-, Raman-, 1H- und 29Si-NMR-Spektren lassen auf ein planares Si2NH-Gerüst, wahrscheinlich C2-Molekülsymmetrie und symmetrische Verteilung der vier Chloratome schließen.1 zeigt sowohl Brönsted- als auch Lewis-Acidität und reagiert mit drei Äquivalenten Pyridin zu HSiCl2(py)2—NH(py)—HSiCl2, mit laut 29Si-Festkörper-NMR-Spektrum einem sechsfach und einem vierfach koordinierten Si-Atom.Die thermische Zersetzung von 1 führt u. a. zum bisher unbekannten 1,3,5-Trichlor-2,4,6-tris(dichlorsilyl)-cyclo-1,3,5-trisil-2,4,6-triazan, Si6Cl9H6N3, 4. Mit Piperidin reagiert 1 unter Substitution der vier Cl-Atome zu Verbindung 5, mit Diazomethan unter Überführung der NH in eine NCH3-Gruppe zu 6. Lithiierungsversuche von 1 führen bevorzugt zur Cl-Substitution durch Alkylgruppen.
    Additional Material: 10 Ill.
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