Dye-sensitized photo-oxygenation

C3 Aryl ttioxanes (75a, 75b) 5 steps (R) Dye-sensitized photo- oxygenation 30 nM (NF54) 10 mgkg i Toxicity studies reved that 11b has a similar tiierapeutic index to artelinic acid 109, no... 

V-Formylkynurenine is one of the 16 autoxidation products of tryptophan (51) (Fig. 8). The dye-sensitized photo-oxygenation of tryptophan in sodium carbonate - acetic acid buffer (pH 7) gave TV-for my Iky n urenine as the major product (52). This is also the oxidation product of tryptophan with hydrogen peroxide (53) and with ozone (54). This is an interesting case the same degradation impurity can be obtained in different ways, probably... 

Nakagawa M, Yokoyama Y, Kato S, Hino T. Dye-sensitized photo-oxygenation of tryptophan. Tetrahedron 1985 41 2125-2132. 

In 1939, Kautsky [5,6] reported experimental evidence for a metastable reactive oxygen molecule and the intermediate in dye-sensitized photo-oxygenation reactions. Kautsky s results were extensive and his conclusions basically correct based on what is known today. However, his proposal was rejected by many reputable scientists (e.g., see Ref. 6) and it was never accepted during his lifetime. 

Wasserman, H.H. and Larsen, D.L. (1972) Formation of 1,4-endoperoxides from the dye-sensitized photo-oxygenation of alkyl-naphthalenes. Journal of the Chemical Society, Chemical Communications, (5), 253-254. 

The oxidation of furans has often been used to express the latent functionality present within this heterocyclic framework, and it results particularly attractive for the synthesis of the widespread butenolides [8c,56]. Dye-sensitized photo-oxygenation of furfural, furoic acid and a- or a,a -unsubstituted furans leads directly to butenolides [8c,56,60d,63]. The presence of a silyl group in a-position enhances the rate of endoperoxide formation and controls the regiochemical outcome of the second-step leading to the related butenolide via a rapid intramolecular silatropic shift [64]. An application of this reaction is shown in Sch. 39 as a step in the synthesis of spongianolide A, an antitumoral natural sestertepenoid [65],... 

Isoxazoles, 1,2,5-oxadiazoles and 1,3,4-oxadiazoles are apparently inert under dye-sensitized photo-oxygenation [74a], while a thiotriamide has been found in the photo-oxygenation of arylthiazole presumably via the undetected endoperoxide in a fashion similar to oxazoles [67,80]. 

Dye-sensitized photo-oxygenation of the norbornenes (189 X = Me) and (190 X = H), which have been synthesized cleanly from the acid (191), occurs in a one-step cyclic process via a dipolar transition state with no evidence for a perepoxide intermediate (189 X = Me) gives the alcohol (190 X = OH) from the corresponding allylically rearranged hydroperoxide along with some exo-alcohol and the ketone... 

Vinylcyclopropanols can be prepared either from the readily available cyclopro-panone hemiacetaP, from 1-hydroxycyclopropanecarboxaldehyde derivativesfrom a,a -dichloroacetone, from the silver Simmons-Smith cyclopropanation of a-ethylenic ketone silyl enol ethers from the dye-sensitized photo-oxygenation of alkylidene-cyclopropanes or from the ring-opening of oxaspiropentanes (cf. Section III.C). Consequently, they become participants of choice in a number of useful chemical transformations (see also Section IV.A). 

The same group of workers have also investigated the dye-sensitized photo-oxygenation of vincadifformine. After reduction of the reaction mixture with sodium thiosulfate, the related 16-hydroxyindolenine derivative 285 was obtained, which (without isolation) was rearranged in acetic acid to vincamine in 46% yield. Tabersonine behaved similarly (277). These results are broadly in agreement with those obtained by L6vy and his collaborators in an independent study of the photochemical oxidative rearrangement of vincadifformine (218). 

Aryl-3,5-dihydroxypyrazoles (543) condense with acetylacetone to afford the novel paraionic 87r-betaines (544). The isomerization (545) -> (546) has been observed. The urazole (547) adds the thioketen NCPhC=C=S to form the heterocycle (548). Dye-sensitized photo-oxygenation of the pyrazolo[l,2-a]benzotriazole (549) yields mainly the epoxide (550). ° ... 

A review on the dye-sensitized photo-oxygenation of indole derivatives has appeared.At low temperature, dioxetan (56) has been obtained from the dye-sensitized oxygenation of indole (57) (Scheme 13) and zwitterionic intermediates have been trapped using nucleophiles such as MeOH, EtOH, and... 

Comparison of Terenin-Schenck Mechanism and the Singlet Oxygen Mechanism. Terenin (49, 50), and later Schenck (47), proposed the following mechanism for dye sensitized photo-oxygenation reactions ... 

The dye sensitized photo-oxygenation of cholest-4-en-3 -ol yields only two products (37, 38), an enone (III) and an epoxy ketone (II) as illustrated. The anomalous aspect of these results is that the enone/epoxy ketone ratio varies by a factor of 150 depending upon the choice of sensitizer. In light of our prediction regarding the variation in the Xg / Ag ratio with Et, we were interested in whether there was a... 

The dye-sensitized photo-oxygenation of the 4//-pyrazole (360 R = Me) yields the diketone AcCMc2Ac. The diphenyl analogue (360 R = Ph) undergoes a stereospecific addition reaction when treated with hydrogen peroxide in... 

Dye-sensitized photo-oxygenation of NN-dimethylhydrazones followed by reduction with triphenylphosphine or dimethyl sulphide and hydrolysis yields the parent carbonyl compounds in fair to good yield. 

Jefford, C. W., A. Exarchou, and P. A. Cadby The Role of Singlet Oxygen as Reagent in the Dye-Sensitized Photo-oxygenation of a-Ketocarboxylic Acids. Tetrahedron Letts 1978, 2053. 

Photochemical and thermal rearrangement of an optically active mixture of E-and Z-2-methyl-3-phenylmethylenecyclopropane leads to an EjZ mixture of phenyl-ethylidenecyclopropane containing the same major, but unidentified, isomer and with the maintenance of chirality.These data show that the stereochemical outcome of the rearrangement is the same in both ground and excited states. Dye-sensitized photo-oxygenation of methylenecyclopropane (290) can proceed by three paths at — 50 °C (paths a—c. Scheme 35), but at higher temperatures path a is followed. ... 

Several preliminary reports of the dye-sensitized photo-oxygenation of pyrrole derivatives to oxygenated pyrrolines have appeared. " 5-Oxopyrrolines may be obtained in good yields by heating acyl-ene-hydrazines with sodium methoxide. The postulated mechanism is shown in Scheme 16. 

Acetyltetronic acid derivatives (94) are formed during base-catalysed rearrangement of 4-ethoxycarbonyl-3(2//)-furanones (93). 3-(Arylmethylene)-furandiones (95) can be obtained in fair yield froni tetronic acid itself (for which an improved preparation has been found) by condensation with aromatic aldehydes (three equivalents ) in the presence of concentrated hydrochloric acid. Butyrolactones are transformed into their 2-keto analogues upon dye-sensitized photo-oxygenation of their readily available 2-dimethylaminomethylene derivatives, the overall yield for the two steps, with model compounds, being about 60%. °"... 

The dye-sensitized photo-oxygenation of hexamethyleneammonium hexa-methylenedithiocarbamate by xanthene dyes and the photolysis of 4-hydroxybenzyl dithiocarbamates are the subjects of two recent papers. A report on the pyrolysis reactions of aryl N-monoalkyldithiocarbamates has also appeared. ... 

Planas, A., Lupon, R, Cascallo, M., and Bonet, J., Product characterization and kinetics of dye-sensitized photo-oxygenation of 9,11-didehydroestrone derivatives,ITe/v. Chim. Acta,72,7 5,1989. 

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