Preparation of 2H‐Benzoxetes by Photoinduced [2 + 2] Cycloaddition of Quinone Methides, Accessible by Dimethyldioxirane (DMD) Oxidation of 2,3‐Dimethylbenzofurans

Irradiation (λ > 366 nm) of the quinone methides 3, which were formed by valence isomerization of the methyl‐, chloro‐, and tert‐butyl‐substituted 2,3‐dimethylbenzofuran epoxides 2, afforded the novel 2H‐benzoxetes 4 by photochemical [2 + 2] cycloaddition. These strained and highly labile benzoxetes 4 were spectrally (1H and 13C NMR) characterized at subambient temperatures. On prolonged storage (2–3 d) at –20 to –10°C, the benzoxetes 4 reverted to the quinone methides 3 and/or benzofuran epoxides 2.