Dehydro­leucodin: a guaiane-type sesquiterpene lactone

Dehydro­leucodin [systematic name: (1S,6S,2R)-9,13-dimeth­yl-5-methyl­ene-3-oxatricyclo­[8.3.0.0(2,6)]trideca-9,12-diene-4,11-dione], C(15)H(16)O(3), is a guanolide isolated from Artemisia douglasiana. The fused-ring system contains a seven-membered ring that adopts a chair conformation, a fused planar cyclo­pentenone ring and a five-membered lactone ring fused in envelope conformation. The absolute structure determined by X-ray analysis agrees with that previously assigned to this compound by NMR studies [Bohlmann & Zdero (1972 ▶). Tetra­hedron Lett. 13, 621–624] and also with that of leucodine, a closely related guaianolide [Martinez et al. (1988 ▶). J. Nat. Prod. 51, 221–228].