Rose Bengal as sensitizer

The intermolecular and intramolecular 13C isotope effects were used in studies of the mechanism of the ene reaction of singlet (1Ag) oxygen with alkenes.89 The intermolecular 13C isotope effect was determined for reaction of 3-isopropyl-2,4-dimethylpent-2-ene 40 with 102 in methanol/2-propanol (1 1) at 10°C using a sunlamp and Rose Bengal as sensitizer. 

Compound (362) gave the trioxane (19) (15%) when reacted with singlet oxygen in the presence of acetaldehyde, using rose bengal as sensitizer, followed by treatment with HC1 (88CC372). 

A detailed study of the photooxygenation of hexene isomers showed that, depending on the reaction temperature (25c or 50 C). the allylic hydroperoxides are produced E selectively38, in diastereomeric ratios from 78 22 to > 99 1. In cases with a high alkene concentration in ethanol as solvent and rose bengal as sensitizer, the product ratios are determined after 5-10% conversion. 

A 2% solution of isoprene in dichloromethane and methanol with methylene blue or rose bengal as sensitizers gives, on irradiation under oxygen with a 500-W iodine lamp, a 50% yield of 4-methyl-l,2-dioxa-4-cyclohexene [52]. Cyclic dienes are converted into bicyclic endoperoxides (equation 132). The naturally occurring ascaridole is thus synthesized from a-terpinene (equation 133) [19, 1115]. 

In the presence of Rose Bengal as sensitizer and under either aerobic or anaerobic conditions, proline is photodecarboxylated to A -pyrroline, and under similar conditions the methyl ester yields an equimolar mixture of A -and A -pyrroline-2-carboxylic acid methyl esters. These observations suggest that the reaction proceeds by a Type I photooxidation. 

Using Rose Bengal as sensitizer, isoquinoline-1,3-diones have been oxidised by 02( Ag) to such products as isoquinoline-1,3,4-triones, methyl 1 -hydroxy-3-oxoisoindole-1 -carboxylates, and 3-hydroxy-3-alkyl(aryl)amino-carbonylbenzoisofuran-l-ones, depending upon the solvent chosen. 02( Ag) generated using tetraphenylporphyrin has also been used, in which... 

The photooxidation of oxopurines such as caffeine, theophylline, theobromine, and 1,3,7-trimethyluric acid using Rose Bengal as sensitizer occurs by a type II mechanism. 3-Methyl-5-(methylamine)-l,5-dehydrohydantoin has been characterised as a reaction product, and evidence is presented which suggests that the initial exciplex formed between 02( Ag) and the oxopurine evolves into a zwitterionic transition state. 

The cis- and trans-1,4-polybutadienes used in this work were obtained from The B. F. Goodrich Research and Development Center, Brecksville, OH, and had initial cis/trans ratios of 98/2 and 2/98, respectively. The procedures for the photosensitized oxidation of purified samples of the 1,4-polybutadienes, using visible light and methylene blue, chlorophyll and Rose Bengal as sensitizers, the procedures for the reduction of the hydroperoxidized polymers to the corresponding alcohols, as well as the procedures for the spectroscopic analysis of the reaction products, were similar to those described previously (8). 

B Competitive experiment using rose Bengal as sensitizer. C Rose Bengal as sensitizer, (kq + k ) calculated as under A, D Rose Bengal as sensitizer. 0.02 x kj. (2,5-... 

Photo-oxidation of the imino-ether (118) (prepared from yohimbine via the 7-chloroindolenine derivative), in the presence of oxygen and potassium cyanide, with Rose Bengal as sensitizer, results in the introduction of a cyano-group into the tryptophan position the product is thus the a-amino-nitrile (119), together... 

A soln. of 8-methoxycaffeine in methanol-chloroform containing Rose Bengal as sensitizer irradiated at room temp, with a 100 w. high-pressure Hg-lamp through a Pyrex cooling jacket with introduction of Og until after 1 hr. Oa-uptake has ceased l-methyl-2,2-dimethoxy-4-melhylamino-3-imidazolin-5-one. Y 78%. -No reaction takes place in the absence of Rose Bengal. F. e. s. T. Matsuura and I. Saito, Tetrahedron 25, 551 (1969). 

Codeine irradiated and treated with Og in 5 1 ferf-butanol-water containing rose Bengal as sensitizer, and the product isolated as the hydrochloride -> crude nor-codeine hydrodiloride, Y 75%. J. H. E. Lindner, H. J. Kuhn, and K. Gollnick, Tetrah. Let. 1972, 1705. 

A soln. of isoprene in dichlorodifluoromethane-methanol irradiated under O, 7 hrs. at 0 with a 500 w. iodine lamp in the presence of methylene blue or rose Bengal as sensitizer 4-methyl-3,6-dihydro-o-dioxin. Y 50%. F. e. in methylene chloride s. K. Kondo and M. Matsumoto, Chem. Commun. 1972, 1332. 

The oxidation products mentioned can also be obtained by oxidation of hexahydrocolupulone with singlet oxygen, which is generated by Irradiation with visible light using Rose Bengal as sensitizer (160). The conversion of the substrate is almost quantitative, but the amounts of hydroperoxide 207 and 4-hydroxy-... 

A soln. of 2-methylfuran in methanol containing a little rose bengal as sensitizer irradiated 58 min. with a 625 W. incandescent lamp in a 02-stream 2-methoxy-5-hydroperoxy-2-methyldihydrofuran. Y 80%. F. e. s. C. S. Foote, G. O. Schenck et al., Tetrahedron 23, 2583 (1967). 

A slurry of 3-ketobisnor-4-cholen-22-al 22-morpholine enamine in dimethyl-formamide containing rose bengal as sensitizer photooxygenated 17.5 hrs. at 15° progesterone. Y ca. 100%. J. E. Huber, Tetrah. Let. 1968, 3271. 

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