Photosensitized oxidation of furans. Part 12. Solvent effects in thermal rearrangement of the 2,5-peroxides of 2,5-unsubstituted furans

Abstract

The formation, thermal stability, and modes of thermal rearrangement of the 2,5-peroxides (1a–i) of 2,5-unsubstituted furans are reported. In apolar solvents the main product of thermal rearrangement is the cis diepoxide (3) accompanied by the epoxyfuranones (6) and (7). These rearrangements are thought to proceed via concerted processes, although no distinction can be made between them and rearrangements via diradicals. In basic solvents the 5-hydroxyfuran-2(5H)-ones (4) and (5) are isolated in high yields. In this case the rearrangements are explained by assuming ion pairs, (18), as intermediates.