Photosensitized oxidation of furans. Part 14. Nature of intermediates in thermal rearrangement of some endo-peroxides of 2-alkoxyfurans: New rearrangement pathway of furan endo-peroxides

2-Methoxy-5-phenylfurans (1a-c) substituted at C-4 with electron-withdrawing groups, by dye-sensitized photo-oxygenation in non-participating solvents, give the endo-peroxides (3a-c) which by thermal rearrangement partly yield the 3H-1,2-dioxoles (14a-c). The latter, which are the first examples of this ring system, are thermally very unstable. Their formation can be deduced only from the products obtained by thermal rearrangement which are structurally related with the thermal rearrangement products of 3H-1,2,4-dioxazoles (10). The behaviour of the furans (1a-c) contrasts with that of the 2-methoxy-5-phenylfurans unsubstituted at C-4 which under the same conditions give carbonyl oxides.