1,721,026 research outputs found
Photosensitized oxidation of furans. Part 7. Solvent effects in thermal conversion of the endo-peroxides of arylfurans
No full textThermal conversion of the endo-peroxides of the arylfurans (1) in a polar aprotic solvent leads to aroylenol esters (4) and diaroyl epoxides (3), the predominance of one over the other being concentration dependent. The results can be rationalized on the basis of the intermediacy of dipolar species, e.g. (6a) and/or (7a - d), which are formed in the first stages of the reaction and can react intra- and/or inter-molecularly. The behaviour of the peroxides (1) in an apolar solvent suggests that in this case the epoxides (3) are predominantly formed by a different route, probably involving an intramolecular synchronous rearrangement
Photosensitized oxidation of furans. Part 13. Trapping reactions of the carbonyl oxides obtained from some 2-methoxy-5-phenylfurans
No full textThe 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 intermediacy in sensitized photo-oxygenation of heterocyclic systems. Further supporting evidence is also reported. In polar non-participating solvents carbonyl oxides (5a-c) partly rearrange to the epoxides (7a-c)
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
No full text2-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
Carbonyl Oxide Chemistry. Part 2. Substituent and Solvent Effects on the Chemical Behaviour of Carbonyl Oxides
No full textPhotosensitized oxidation of furans. III. Comparison between photochemically and thermally generated singlet oxygen oxidation of 3‐methoxycarbonyl‐2‐methyl‐5‐phenylfuran
No full textThermal conversion of furan endo‐peroxide I, obtained by photosensitized oxidation of furan II, yields very similar results to those of the oxidation of the furan II by thermally generated singlet oxygen, showing that also in the latter case the endo‐peroxide I is the key intermediate. A mechanistic interpretation of the furan II‐singlet oxygen reaction is reported. Copyright © 1981 Journal of Heterocyclic Chemistr
Photosensitized Oxidation of Furans; Part 17: A Simple Method for the Synthesis of 5-Hydroperoxyfuran-2(5H)-ones
No full text- …
