PREPARATION OF 2H-BENZOXETES BY PHOTOINDUCED [2+2] CYCLOADDITION OF QUINONE METHIDES, ACCESSIBLE BY DIMETHYLDIOXIRANE (DMD) OXIDATION OF 2,3-DIMETHYLBENZOFURANS

Irradiation (lambda > 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 (H-1 and C-13 NMR) characterized at subambient temperatures. On prolonged storage (2-3 d) at -20 to -10-degrees-C, the benzoxetes 4 reverted to the, quinone methides 3 and/or berizofuran epoxides 2.