α-Costic anhydride.

THE TITLE COMPOUND [SYSTEMATIC NAME: 2-(4a,8-dimethyl-1,2,3,4,4a,5,6,8a-octa-hydro-naphthalen-2-yl)acrylic acid anhydride], C(30)H(42)O(3), is a new isocostic anhydride which was synthesized from the aerial part of Inula Viscosa- (L) Aiton [or Dittrichia Viscosa- (L) Greuter]. The mol-ecule adopts an essentially linear shape with two terminal fused-rings bridged by the anhydride group. The external rings have the same conformation (half-chair) while each of the two inner rings has an almost ideal chair conformation. In the crystal, inter-molecular C-H⋯O inter-actions link the mol-ecules into a two-dimensional array in the bc plane.