The acid-catalyzed isomerization of (-)-thujopsene (1) under nonaqueous conditions proceeds principally via the isolable spiro olefin intermediates a-and 0-chamigrene (8 and 9) to a complex mixture of isomeric tricyclic olefins. The major component of this complex mixture is rigorously shown to be 7, 10-ethano-4, 4, 7-trimethyl-1 (9)-octalin (10).
