The title compound, C17H24O5, featuring a 2-carbeth-oxy-3-oxepanone unit in its intra-molecularly O-H⋯O hydrogen-bonded enol form, was obtained via [(CF3CO2)2Rh]2-catal-ysed intra-molecular O-H bond insertion in the α-diazo-ω-hy-droxy-β-ketoester, ethyl 4-[(1S,3aS,6R,6aS)-6-hy-droxy-2,2,3a-trimethyl-3-oxo-octa-hydro-penta-len-1-yl]-2-diazo-3-oxobutano-ate. The seven-membered oxacyclic ring, thus constructed on a cis-fused diquinane platform, was found to adopt a distorted boat-sofa conformation.