Cyclopropylidenecyclobutenes and-cyclobutanes were conveniently prepared using the Petasis titanocene approach. The cyclobutenes were unreactive to singlet oxygen, reacting sluggishly via a photoinitiated free radical autooxidative epoxidation process, to yield the corresponding spiroketones. By contrast, cyclopropylidenecyclobutanes react rapidly with 1O2, via an 'ene'process, initially generating a cyclopropyl hydroperoxide, which proceeds ...
