Applications synthétiques de la cyclisation d'alcools tertiaires γ‐éthyléniques en α‐bromotétrahydrofurannes sous l'action du N‐bromosuccinimide. I. Synthèse facile de la triméthyl‐2,2,5‐cycloheptène‐4‐one ou karahanaénone à partir du linalol

The ionic reaction of linalool and N‐bromosuccinimide in CCl4 at room temperature afforded 2‐methyl‐2‐vinyl‐5‐(1‐bromo‐1‐methyl‐ethyl)‐tetrahydrofuran (I). On treatment with refluxing collidine this compound yielded the intermediate allyl vinyl ether III, which immediatealy rearranged to 2,2, 5‐trimethylcyclohept‐4‐en‐one (V) or «karahanaenone» through a [3,3]‐sigmatropic process. Karahanaenone, a constituent of hop oil, was thus synthesized for the first time (overall yield 62% from linalool). The mechanisms of these reactions are discussed.