Application of an S→O allylic transposition in the context of a bridgehead olefinic system.: New opportunities for the structural modification of bicyclo[6.2.1]undecanes via transannular ring closure

A practical route is described for the preparation of allylic sulfide 8, whose double bond resides at a bridgehead site, Following hydride reduction of the ketone carbonyl and sulfoxidation, exposure to trifluoroacetic anhydride results in the operation of an intermolecular S --> O allylic transposition, This central step leads to 14a, an intermediate useful for probing the consequences associated with epoxidation of its cis-cyclononene double bond. A total of three different transannular cyclizations are described in order to demonstrate the ease with which ring closures can operate in a medium-ring setting of this type. Represented are transformations that generate tetrahydrofuran, oxetane, and cyclopropane subunits. The kinetic biases favoring these transformations are highlighted.