Nature of the 5-norbornen-2-yl Cation Intermediate in the acetolysis of 2-deuterio-endo-5-norbornen-2-yl brosylate

✍ Scribed by Pierre Vogel; Roland Delseth; Daniel Quarroz

• Publisher: John Wiley and Sons
• Year: 1975
• Tongue: German
• Weight: 814 KB
• Volume: 58
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19750580220

✦ Synopsis

Abstract

Mass spectrometrical and ^1^H‐NMR.‐analyses of the exo‐5‐norbornen‐2‐yl acetate, formed by acetolysis of endo‐5‐norbornen‐2‐yl‐2‐exo‐d brosylate, demonstrate that the deuterium initially on C(2) migrates partially (30%) onto C(1) (mechanism Ia or Ib). No deuterium could be detected on the other positions, which shows that C(1–7) migration is insignificant. ^13^C‐NMR.‐analysis of the deuteriated nortricyclyl acetate obtained as main product shows that the deuterium is equally and uniquely distributed between positions C(1) and C(6). This indicates that the nortricyclyl derivatives do not arise from nucleophilic attack on C(5) of asymmetrical norbornenyl intermediates, but from the reaction of a symmetrical nortricyclyl cation intermediate with solvent (mechanism Ib).

Since the pioneering work of Roberts [1] and Winstein [2] on the solvolysis of exo‐ and endo‐5‐norbornen‐2‐yl derivatives 1‐X and 2‐X many papers have dealt with the cationic intermediate, the nature of which has still not been established satisfactorily [3]. We discuss briefly the main features of this homoallylic system and present experimental results that allow, for the first time, a clear distinction between five possible mechanisms Ia, Ib, II, III and IV of the degenerate rearrangement of the cationic intermediate formed in the acetolysis of the endo‐5‐norbornen‐2‐yl brosylate.