Optical Activation of Some Chiral Aldehydes via 1-Methylpiperazine Enamines

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  • YOKOWO Yasuhiko
    Department of Synthetic ChemistrA Faculty of Engineering, The University of Tokyo
  • SAKURAI Takao
    Department of Synthetic ChemistrA Faculty of Engineering, The University of Tokyo
  • SABURI Masahiko
    Department of Synthetic ChemistrA Faculty of Engineering, The University of Tokyo
  • YOSHIKAWA Sadao
    Department of Synthetic ChemistrA Faculty of Engineering, The University of Tokyo

Bibliographic Information

Other Title
  • 1-メチルピペラジン類エナミンを経由するアルデヒド類の光学活性化
  • １‐メチルピペラジン類エナミンを経由するアルデヒド類の光学活性化

Description

Optical activation of 2-phenylpropionaldehyde (PPA) and 3-(p-cumy1)-2-methylpropionaldehyde (CPA) via enamines has been studied, employing (S)-2-isopropyl-1-methylpiperazine J and (S)-3-isopropyl-1-methylpiperazine [2] as the se c[o1n] dary amine components of the enamines. Whe, n [2] J was used as the amine component, the optical rotation of CPA recovered by hydrolysis of the enamine was significantly dependent on the acids. However, the optical rotation of CPA from the enamine of [1] J was found to be moderately positive and almost constant. The 1H-NMR spectrum of the iminium salt of CPA enamine of [1]showed the signals of the isopropyl substituent of the piperazine shifted slightly to the higher field (Table 3). The occurrence of the CH-π interaction between the isopropyl substituent o f the piperazine and the phenyl group in the aldehyde moiety was suggested (Scheme 4).<BR>From the deuterium labeling experiments of the enamines, the optical activation of CPA via the enamine with [2] was considered to be kinetically controlled, while that of the enamine with Li J to be thermodynamically controlled. This would coincide with the presence of the iminium salt stabilized by the CH-n-interaction. An explanation on the dredominant formation of S(+)-CPA was given, based on the expected preference of one of the possible iminium salts, (S)-salt, over another, (R)-salt, from stereochemical points of view (Scheme 4).

Journal

  • NIPPON KAGAKU KAISHI

    NIPPON KAGAKU KAISHI 1981 (12), 1904-1910, 1981-12-10

    The Chemical Society of Japan

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