(1S,4R,5R,6R)‐6‐Methoxycarbonyl‐4‐pivaloyloxy‐2‐(pivaloyloxymethyl)bicyclo[3.1.0]hex‐2‐ene‐1‐carboxylic acid

The stereochemistry of the title compound, C₂₀H₂₈O₈, a key step in the preparation of analogues of mannostatins, potent inhibitors of α‐mannosidase, has been established. The carboxyl­ic acid group at C1 unexpectedly eclipses the C1—C2 bond. The cyclo­propane ring makes a dihedral angle of 109.4 (2)° with the cyclo­pentene ring.