Cyclodextrins photochemical processes

The photochemical process built into 7 was encountered previously with regard to 2, Le, the capability of 02 in quenching excited states of sufficiently long lifetimes. In the case of 7, the process is so efficient that ambient levels of 02 completely kill off phosphorescence, even if the phosphor is enveloped by p-cyclodextrin. 

The amide (38a) is photochemically inert on irradiation in ether. The related compound (38b) is, however, photochemically reactive and undergoes fission by a Norrish Type II process to yield a mixture of products.The results of a study of the enantioselective photodeconjugation reactions of the lactones (39) have been published. The behaviour of the ketones (40) and (41) in the isotropic and the two solid phases of heneicosane (CcxH ) has been evaluated. The influence of the various phases on the ratio of elimination to cyclization products of the ketones was discussed. The modification of the photoreactivity of ketones (42) in cyclodextrin has been... 

Norrish Type I cleavage of benzylketones occurs very readily to yield benzyl and acyl radicals. In competition with other processes, these can couple by attack of the acyl radical upon the aromatic nucleus of the benzyl radical to give as a product an acyl toluene derivative. Turro has examined the photochemical properties of the 2-phenylalkanones (326) in solution and complexed with cyclodextrins. In solution the major fate of the Type I biradicals formed is intr2unolecular recombination by attack of the acyl radical at the para position of the benzyl radical to generate (327). However, complexatlon of (326) within the cyclodextrin cavity inhibits formation of (327) and promotes disproportionation of the blradicals to give (328). Turro has also examined the photochemistry of dlbenzylketone Included in zeolites.Recombination of the Type I radicals in this case can produce a mixture of (2-methyl-phenyl) benzylketone and (4-methylphenyl)benzylketone decarbonylation of the acyl radical competes and leads to the isolation of 1,2-dlphenylethane. It is found that the relative yields of the products... 

Mori et al. have studied the decarboxylation of (39) under a variety of conditions and have found that the conversion to (40) occurs without the involvement of radicals. They suggest that the process is a concerted cheletropic extrusion via the s-cis conformation. A further study has examined the photodecarboxylation of the (5)-ester (39) in unstretched-polyethylene films. The decarboxylation affords (40) with complete retention of the stereochemistry. The yield of product is 98% and the ee is >98%. The photochemical behaviour of the ester in other confining media such as cyclodextrins indicates that cage-escape products are also formed. The irradiation of grandifloric acid (41) at 254 nm in acetonitrile brings about decarboxylation with the formation of epimers. In methanol a different reaction occurs that results in the conversion of the C-methyl group into a carbomethoxy substituent. ... 

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