Browsing by Author "Stelzer, Uwe"

Filter results by typing the first few letters
Now showing 1 - 5 of 5
  • Thumbnail Image
    ItemOpen Access
    Darstellung und stereoselektive Reaktionen von (R)-α-Sulfonyloxynitrilen
    (1991) Effenberger, Franz; Stelzer, Uwe
    Hier berichten wir über eine wichtige Erweiterung des Synthesepotentials optisch aktiver Cyanhydrine durch Uberfiührung der Hydroxygruppe in eine gute Austrittsgruppe. Besonderes Interesse kommt dabei den Reaktionen der Cyanhydrinderivate zu, bei denen der Stickstoff der Cyangruppe im Molekül erhalten bleibt, da Verbindungen dieses Typs nicht direkt iüber α-Amino- oder α-Hydroxycarbonsäuren zugänglich sind.
  • Thumbnail Image
    ItemOpen Access
    Darstellung von (R)-2-(Sulfonyloxy)nitrilen und ihre Reaktionen mit Acetaten : Konfigurationsumkehr optisch aktiver Cyanhydrine (Enzym-katalysierte Reaktionen ; 15)
    (1993) Effenberger, Franz; Stelzer, Uwe
    2-(Sulfonyloxy)nitriles (R)-6, 7, 8 are obtained in high optical purity from the respective cyanohydrins (R)-2 by sulfonylation with methanesulfonyl chloride (3), toluenesulfonyl chloride (4), and trifluoromethanesulfonic anhydride (5), respectively. In contrast to the aliphatic (sulfonyloxy)nitriles (R)-6, 7, 8a - e, the benzylic-type mandelic acid derivatives (R)-7,8í are unstable at higher temperature. The 2-(sulfonyloxy)nitriles (R)1- 6, 7, 8a - e react at room temperature with alkali acetates in a typical SN2 manner to give the cyanohydrin acetates (S)-9 in high optical purity. Under these reaction conditions, however, the mandelic-type compounds (R)-7, 8í partly racemize and decompose. By hydrolysis of the acetates (S)-9, (S)1-cyanohydrins (S)-2 of aliphatic aldehydes are easily available.
  • Thumbnail Image
    ItemOpen Access
    Eine neue Synthese von Didehydrodipeptiden und Didehydrotripeptiden (Aminosäuren ; 17)
    (1993) Effenberger, Franz; Kühlwein, Jürgen; Hopf, Martin; Stelzer, Uwe
    Esters of N-phthaloyl-protected (R)- or (S)-didehydro dipeptides 5-7 were obtained in good yields by the perrhenate-catalyzed decomposition of 2-azidocarboxylates 1 with N-phthaloyl-protected (R)- or (S)-amino acid chlorides 2 in presence of at least equimolar amounts of N-methyl-2-pyridone (4) as acylation catalyst. Esters of didehydro tripeptides 16 were obtained in a comparable procedure from the optically active amino acid chlorides 2 and 2-(2-azidoacyl)amino acid esters 15, which were prepared from 2-azidocarboxylic acids 12 or the corresponding chlorides 13 with 2-amino acid ester hydrochlorides (S)-14. - As an example, the unprotected (S)-alanly-didehydrovalin 20 was prepared from the didehydro dipeptide 18a without any racemization by hydrolysis of the benzyl ester and subsequent hydrogenolytic removal of the N-phthaloyl group.
  • Thumbnail Image
    ItemOpen Access
    Preparation of (S)-2-fluoronitriles
    (1993) Stelzer, Uwe; Effenberger, Franz
    (S)-2-fluoronitriles (S)-4 are obtained in good chemical and high optical yields from (R)-cyanohydrins (R)-2 or (R)-cyanohydrin trimethylsilylethers (R)-3 by fluorination with DAST or by nucleophilic substitution of α-sulfonyloxynitriles (R)-6,7 with fluoride on polymeric supports (Amberlyst A-26 F−) under inversion of configuration of the starting cyanohydrins.
  • Thumbnail Image
    ItemOpen Access
    Synthesis and stereoselective reactions of (R)-α-sulfonyloxynitriles
    (1991) Effenberger, Franz; Stelzer, Uwe
    We report here on an important extension of the synthetic potential of optically active cyanohydrins by conversion of the hydroxy group into a good leaving group. Of particular interest are reactions of the cyanohydrin derivatives in which the nitrogen of the cyano group remains in the molecule, since compounds of this type are not directly accessible via α-amino- or α-hydroxycarboxylic acids.