Bromination and Accompanying Rearrangement of the Polycyclic Oxetane 2,4-Oxytwistane

Bromination of the polycyclic oxetane 2,4-oxytwistane (rac-(1R,3S,4R,7S,9R,11S)-2-oxatetracyclo[5.3.1.03,11.04,9]undecane) was undertaken in order to form 2,4-dibromotwistane. The oxetane was subjected to the mild reagent combination CBr4/Ph3P in a fashion similar to that for the Appel and Corey–Fuchs reactions. NMR spectroscopy revealed that the isomeric dibromo compound 2,8-dibromoisotwistane (2,8-dibromotricyclo[4.3.1.03,7]decane) was inadvertently formed. The conversion was prevented by migration of a C–C bond within the geometrically stressed C10 framework. Computational chemistry was used to model the structure of the polycyclic oxetane and to assess the component of total ring strain energy due to the four-membered heterocycle. Mechanistic aspects behind the skeletal rearrangement are also discussed.