Dimethyldioxirane epoxidation of benzofurans: reversible thermal and photochemical valence isomerization between benzofuran epoxides, quinone methides, and benzoxetenes
Low-temperature oxidation of the four possible regioisomeric methoxy-substituted benzofurans 1 by dimethyldioxirane afforded the rather labile epoxides 2, which are in equilibrium with their equally labile quinone methides 3 through reversible valenceisomerization. Photochemical cyclization of the latter afforded the hitherto unknown benzoxetenes 4, which are sufficiently persistent at subambient