Photooxygenation furan

Benzo[b]furan, 2,3-dihydro-2-phenyl-synthesis, 4, 697 Benzo[b]furan, 2,3-dihydroxy-tautomerism, 4, 37 Benzo[6]furan, 4,6-dimethoxy-acylation, 4, 606 Benzo[6]furan, 2,3-dimethyl-acetylation, 4, 606 bromination, 4, 605 photooxygenation, 4, 642 Benzo[b]furan, 5,6-dimethyl-2,3-diphenyl-applications, 4, 709 Benzo[b]furan, 1,3-diphenyl-vertical ionization potential, 4, 587 Benzo[b]furan, 2-ethoxy-5-hydroxy-synthesis, 4, 127... 

Some unusual pyridazine syntheses were reported. A dye-sensitized photooxygenation reaction of ribofuranosyl furans gave a new entry to pyridazine C-nucleosides 14... 

The photooxygenation of furans in the presence of acetaldoxime, followed by Et2S reduction and treatment with Si02, leads to l,2-oxazin-6-ones 361 in 37-50% yields (equation 157) . ... 

The main types of substrates investigated so far are polycyclic aromatic compounds, aryl substituted carbo- and heterocyclic pentadienes, cyclic 1,3-dienes, furans, and olefins. It has turned out that type II photooxygenation of these compounds in solution occurs via the oxygen-activation mechanism. 

Cyclopentadienes, 1,3-cyclohexadienes, 1,3-cycloheptadienes, as well as furan and aklyl-substituted furans, have been investigated as substrates of photosensitized oxygenation reactions, while aromatic compounds such as anthracenes and tetracenes as well as aryl-substituted carbo-and heterocyclic pentadienes were studied in direct and indirect (photosensitized) photooxygenation reactions. 

Diaryl- and tetraaryl-substituted furans such as tetraphenylfuran (384) for example, yield generally cw-diaroylethylenes such as 380, probably via intermediate ozonide formation.257 Secondary reactions seem to depend very much on the nature of the solvents. Thus, cis-dibenzoylstilbene (380) has been observed by direct photooxygenation of 384 in CS2 as well as by methylene blue-sensitized photooxygenation of 384 in methanol.257,258 However, when the latter reaction was carried out in acetone, epoxide 386 and the enolbenzoate 387 were obtained.258... 

Detailed accounts on the photooxygenation of 1,3-diphenyl-benzo[c]furan (and other benzo [cjfurans " ) reveal a dual mechanistic process. In the high concentration region 138 reacts in its ground state with singlet oxygen (generated either by dye sensitization [Scheme 15,... 

Acenaphtho[l,2-c]furan 317 has been obtained in high yield through sensitized photooxygenation of cyclopentadienol 316 and subsequent treatment with acid hemiketals of the type described above are involved. The rhodium complex pathway to 317 was unsuccessful oxidation of 319,... 

Benzo[6]furan and 2-methylbenzo[6]furan fail to undergo photooxygenation but 2,3-dimethyIbenzo[6]furan yields 2-acetoxyacetophenone (364). At -78 °C the peroxide (363) is produced which at higher temperature rearranges to the acetophenone (364 Scheme 98). 2-Vinylbenzo[6 Jfurans, e.g. trans- 2- styrylbenzo[6 Jfuran (365 Scheme 99), yield photooxides which may be isolated. Compound (366) on treatment with a catalytic amount of triethylamine yields the lactone (367) (77BCJ3026). 

Benzo[c]furans undergo very rapid photooxidation. 1,3-Diphenylbenzo[c ]furan yields the oxide (368) on sensitized photooxygenation in ether at -50 °C. Reduction of the oxide with potassium iodide in acetic acid affords 1,2-dibenzoylbenzene and reaction with methanol supplies the hydroperoxide (369). 

The regioisomers of 3,3,4-trisubstituted l,2,4-dioxazolidine-3-ones 149 were obtained by the [3+2] reactions of carbonyl oxides 144 with phenylisocyanate, where the latter was used as a solvent. Initial carbonyl oxides 144 were generated by photooxygenation of furan derivatives 147 through peroxide intermediate 148 (Scheme 42) <1994J(P1)3295>. 

Two examples are presented in which the intramolecular nucleophilic attack of adjacent alcohol groups led to the formation of spiro compounds (Schemes 11.12 and 11.13). In 2008, spirolactone 80 was synthesized in CH2C12 from an MB-sensitized photooxygenation of furan 79 [82]. A possible mechanism, with an... 

The p-peroxide 84 was obtained by methylene blue-sensitized photooxygenation of diene 83 together with its a-isomer (2 1 9,13-a p) and was separated by silica gel chromatography. Diepoxides are the thermally rearranged products of a.a -unsubstituted or alkylsubstituted furan endoperoxides [59,60d,g]. 

For example, photooxygenation of 2,3-dimethylbenzo[b]furan at —78 °C produced dioxetane 89, which isomerized at room temperature to give 2-acetoxyacetophenone (as shown in Scheme 49) <1995ACR289>. 

A solution of 18.5 mg (0.08 mmol) of (3a, 8a7 ,9a7 )-3a,4,6,7,8,8a,9.9a-octahydro-9,8-dimethyl-3-methylene-naphtho[2,3-h]furan-2(3.ff)-one and 2 mg of methylene blue in 10 mL of ethanol is photooxygenated for 8h at 22 + 2 °C. using a constant oxygen flow and a medium-pressure 400-W mercury lamp with a 1-cm filter width and filtering through a 2% aq sodium nitrite solution. The solvent is then evaporated in vacuo and the residue chromatographed (silica gel, hexane/EtOAc 4 1) to give an oil yield 12 mg (57%) [[Pg.444]

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