[(2S,3aR,6aR)-5-Oxohexa-hydro-furo[3,2-b]furan-2-yl]methyl acetate.

The title compound, C9H12O5, is a bicyclic lactone, presenting a 2,6-dioxabi-cyclo-[3.3.0]octan-3-one skeleton, which was obtained through an intra-molecular lactonization. The bicyclic lactone presents a cis ring-junction and a 1,5-trans-substituted tetra-hydro-furan. Both five-membered rings are in twisted envelope conformations with one of the fused C atoms as the flap. The dihedral angle between the mean planes of the bicyclic lactone residue, defined by the di-hydro-furan-2(3H)-one and the tetra-hydro-furan rings, is 69.5 (2)°. The atoms of the ester chain are coplanar [maximum deviation = 0.013 (2) Å]. The absolute structure was not determined.