Optically active 1-alkoxybicyclo[4.1.0]heptane wasconverted using zinc iodide as a catalyst to2-alkoxymethylidenecyclohexane without loss of optical purity. Themechanism of the isomerizationwas studied using a stereochemical analysis of the product anddeuterium labeling experiments.The results indicated that the isomerization takes place through astepwise mechanism that involvesan attack of zinc iodide on the cyclopropane ring to cause ringopening, followed by an intramolecular1,2-hydride shift with liberation of the zinc iodide.