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Laschat, Sabine; Grehl, Matthias

Diastereoselective Synthesis of α‐Hydroxy‐ and α‐Aminoindolizidines and ‐quinolizidines. Evidence for a Novel Cyclization/Hydride Migration Mechanism in the TiCl4‐Induced Reaction of Prolinal Benzylimines by Deuterium Labeling Studies

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  • Medientyp: E-Artikel
  • Titel: Diastereoselective Synthesis of α‐Hydroxy‐ and α‐Aminoindolizidines and ‐quinolizidines. Evidence for a Novel Cyclization/Hydride Migration Mechanism in the TiCl4‐Induced Reaction of Prolinal Benzylimines by Deuterium Labeling Studies
  • Beteiligte: Laschat, Sabine; Grehl, Matthias
  • Erschienen: Wiley, 1994
  • Erschienen in: Chemische Berichte
  • Sprache: Englisch
  • DOI: 10.1002/cber.19941271027
  • ISSN: 0009-2940
  • Schlagwörter: Inorganic Chemistry
  • Entstehung:
  • Anmerkungen:
  • Beschreibung: <jats:p>Lewis acid‐catalyzed cyclization of prolinal and 2‐piperidine‐carbaldehyde benzylimines <jats:bold>11, 12</jats:bold> results in the diastereoselective formation of α‐amino‐β‐alkyl‐substituted indolizidines <jats:bold>15, 17, 19, 21</jats:bold> and ‐quinolizidines <jats:bold>16, 18, 20</jats:bold>, respectively. Both diastereoselectivity and constitution depend on the Lewis acid. FeCl<jats:sub>3</jats:sub> yields α,β‐<jats:italic>trans</jats:italic>‐α‐(benzylamino)‐β‐isopropenyl derivatives <jats:bold>15</jats:bold> and <jats:bold>16</jats:bold>, probably by a cationic cyclization via carbenium ions <jats:bold>32a, b.</jats:bold> In contrast, TiCl<jats:sub>4</jats:sub> yields α,β‐<jats:italic>cis</jats:italic>‐α‐(benzylideneamino)‐β‐isopropyl derivatives <jats:bold>19</jats:bold> and <jats:bold>20</jats:bold> by a novel cyclization/intermolecular hydride transfer mechanism, which was supported by deuterium labeling studies. Compounds <jats:bold>15, 16, 19</jats:bold>, and <jats:bold>20</jats:bold> were converted to the diastereomeric acetamides <jats:bold>24, 25</jats:bold> and <jats:bold>28, 29</jats:bold>. By an analogous cyclization of the aldehydes <jats:bold>8</jats:bold> and <jats:bold>9</jats:bold> only α,β‐<jats:italic>cis</jats:italic>‐α‐hydroxy‐β‐isopropenylindolizidines <jats:bold>51</jats:bold> and ‐quinolizidines <jats:bold>52</jats:bold> were obtained irrespective of the Lewis acid used. The structures of <jats:bold>30</jats:bold> and <jats:bold>52</jats:bold> were elucidated by X‐ray analysis.</jats:p>