Intermolecular additions of cyclobutanone derived radicals. A convergent, highly efficient access to polycyclic cyclobutane containing structures

α-Xanthyl cyclobutanones undergo intermolecular radical additions to olefins bearing various functional groups. Adducts containing a phosphonate can be made to cyclise by an internal Wittig–Horner–Emmons reaction to give cyclohexene and cycloheptene rings fused to the cyclobutane.