Anomalous Stereochemistry of Gas-phase Acid-induced Ring-opening In 1-phenylcyclohexene Oxide

The nature and stereoisomeric distribution of neutral products obtained from the gas-phase attack of radiolytically formed Broensted and Lewis acids on substituted 1,2-epoxycyclohexanes were studied under different exptl. conditions. Highly regio- and stereoselective cationic nucleophilic displacements, with complete inversion of configuration at the reaction center, were obsd. In some cases, extensive acid-induced isomerization became the only observable pathway. The relative extent of competing substitution and isomerization depend on several factors, including the structure features and internal-energy excess of the oxonium derivs. of the epoxy substrates.