(−)-Istanbulin A

The title compound (systematic name: 9a-hydr­oxy-3,4a,5-trimethyl-4a,6,7,8a,9,9a-hexa­hydro-4H,5H-naphtho[2,3-b]furan-2,8-dione), C(15)H(20)O(4), is a sesquiterpene lactone showing the typical eremophilanolide skeleton, which has been isolated from the plant Senecio candidans collected in the Chilean Magallanes region. The present study confirms the atomic connectivity assigned on the basis of (1)H and (13)C NMR spectroscopy, as well as the relative stereochemistry of the 4α-methyl,5α-methyl,8β-hydr­oxy,10β-H unit. The crystal structure is stabilized by inter­molecular O—H⋯O hydrogen bonds involving the hydr­oxy group as donor and the oxo group as acceptor, giving chains along the a axis. The absolute structure was not determined because of the lack of suitable anomalous scatters.