Photosensitized oxidation of furans. Part 13. Trapping reactions of the carbonyl oxides obtained from some 2-methoxy-5-phenylfurans

Abstract

The dye-sensitized photo-oxygenation in methanol of the 2-methoxy-5-phenylfurans (1a–c), unsubstituted at C-4 with electron-withdrawing groups, leads to the hemiperacetals (4a–c). The reaction provides the first incontrovertible evidence for carbonyl oxide intermediary in sensitized photo-oxygenation of heterocyclic systems. Further supporting evidence is also reported. In polar nonparticipating solvents carbonyl oxides (5a–c) partly rearrange to the epoxides (7a–c).