Behavior of 9-Cyclopropyl-10,10-dimethyl-9,10-dihydrophenanthren-9-ol in Acid Medium: Opening of the Cyclopropane Ring

According to the NMR data, opening of the cyclopropane ring in carbocations derived from 9-cyclopropyl-10,10-dimethyl-9,10-dihydrophenanthren-9-ol in acid medium follows two pathways, depending on the acidity. The first pathway is protonation of the cyclopropyl group; it occurs in strongly acidic medium (HSO3F–SbF5–SO2ClF–CD2Cl2). The second pathway involves cyclopropyl–carbinyl rearrangement; it is typical of less acidic medium.