AbstractFunctionalized cyclopropyl ketones have been found to undergo facile reductive cyclopropane ring opening with samarium (II) diiodide in the presence of a proton source. These reactions were exceedingly rapid, taking place in most cases at −78°C under neutral conditions. An ester group substituted at the C2position of the cyclopropane ring played an important role in the ring opening of cyclopropyl keton