Isopropylidenecyclobutanes 2-5 underwent facile ene reaction with singlet dioxygen, yielding (upon Ph3P reduction) the corresponding pairs of epimeric allylic alcohols 9 and 10, ll and 12, 13 and 14, and 15 and 16, respectively. A combination of spectral evidence and molecular modeling studies were utilized in the structural assignment of the epimers. The data clearly indicate that steric considerations play an important role in determining ...