Photochemical reactions reaction Photo-Fries rearrangement

Photo-Fries rearrangement of aryl esters or its participation in addition to other photochemical reactions was reported in numerous papers concerning low-molecular78 or macromolecular79,63 compounds. 

In this contribution we have presented the synthesis of the new photoreactive thiol MUAP bearing a photoreactive phenyl ester. This molecule is well suited for the preparation of SAMs on gold substrates and can be photochemically modified by UV-illumination due to the photo-Fries rearrangement leading to the formation of hydroxyketones. By a subsequent post-modification reaction with a fluorinated compound low-energy surfaces are attainable. 

A full paper has appeared expanding on the previous report concerning the photo-Fries rearrangements of N-aroylcarbazoles. In polar solvents mixtures of carbazole and both (311) and (312) are obtained, while in non-polar solvents carbazole and low yields of (311) only are isolated instead. An intramolecular cyclisation reaction competed successfully with rearrangement in the case of N-(ortho-chlorobenzoyl)carbazole to yield (313) as the major product. In a report from a different laboratory the photo-Fries rearrangement of N-sulphonylcarbazole is described and the products identified as (314) and (315) in contrast to the results described above, these authors report that N-benzoylcarbazole is photochemically inert. 

Several reviews have been published within the year which are of general relevance to the photoreactions of aromatic compounds. The subjects of these reviews include photochemistry in ionic liquids and in isotropic and anisotropic media, organic synthesis utilizing photoinduced electron-transfer reactions," heteroatom-directed photoarylation processes, photochromism, and photochemical molecular devices. Reviews more directly pertinent to the sections in the present chapter include those of the photoisomerization of five-membered heteroaromatic azoles, the photocycloaddition of benzene derivatives to alkenes, Diels-Alder additions of anthracenes, advances in the synthesis of polycyclic aromatic compounds, diarylethene-based photochromic switches, the photo-Fries rearrangement, and the application of Diels-Alder trapping of photogenerated o-xylenols to the synthesis of novel compounds. " A number of chapters in the two recently published handbooks of photochemistry and photobiology and in the revised edition of the text on photochromism are also pertinent to the current subject matter. 

The photochemical reactivity of P-ketoesters is different form that of P-diketones. Irradiation of a P-ketoester in the presence of an alkene produces oxetane via the ketone carbonyl instead of the desired cyclobutane ring system. Therefore, it is necessary to covalently lock the ketoesters as the enol tautomers. To this end, silyl enol ethers, 129 and 132a, and enol acetates, 130 and 132b, were prepared, but these substrates still fail to undergo the desired intramolecular [2 + 2] photocycloaddition with olefins. The only new products observed in these reactions result from the photo-Fries rearrangement of the cyclic enol acetate (130 to 131) and cis-trans isomerization of both acyclic substrates 132a/b. However, tetronates are appropriate substrates for both intermolecular and intramolecular photocycloadditions with olefins. In addition, enol acetates and silyl enol ethers of p-keto esters are known to undergo [2 + 2] photoaddition with cyclic enones (vide infra). 

The photo-Fries rearrangement has been used in various synthetic reactions. A recent application concerned the synthesis of the mitomycin precursor (148) in high yield from the lactone (147). Finally, reference is made to the efficient photochemical deconjugation of piperidine esters (149) to the endocyclic isomers (150), presumably by a photoenolization reaction. ... 

Gu, W. Q., Bi, S. G., and Weiss, R. G., Photo-Fries rearrangements of 1-naphthyl esters in the glassy and melted states of poly(vinyl acetate). Comparisons with reactions in less polar polymers and low-viscosity solvents, Photochem. PhotobioL Sci., 1, 52, 2002. 

For some selected reviews on Photo-Fries rearrangements, see (a) Martin, R., Uses of the Fries rearrangement for the preparation of hydroxyarylketones. A review, Org. Prep. Proc. Int., 24, 373M 35, 1992 (b) Pfau, M. and Julliard, M., Reactions photochimiques des esters aromatiques. Bull. Chem. Soc. Fr., 785-802,1977 (c) Bellus, D., Photo-Fries rearrangement and related photochemical [l,j]-shifts (j = 3,5,7) of carbonyl and sulfonyl groups, Adv. Photochem., 8,109-159,1971. 

Aryl sulfonates RS03Ar (R = C6H5, CH3) were found to undergo photochemical rearrangement upon irradiation with uv-light.8,9 In the case of phenyl p-toluenesulfonate (20), products originating from the photo-Fries reaction were identified as 2-hydroxy-4 -methyldiphenyl sulfone (21), 4-hydroxy-4 -methyldiphenyl sulfone (22), and phenol (23). 

Secondary rearrangements apparent isomerizations through radical recombination reactions. In the rearrangement reactions considered so far, the isomerization step is the primary photochemical process, except when a biradical is formed as an intermediate for in that case the primary photochemical process is really a dissociation, even though the fragments cannot separate. There are however cases of overall isomerizations which result from the recombinations of separated free radicals formed through a process of photodissociation. The photo-Fries reaction is an important example of this mechanism, and is illustrated in Figure 4.43. 

Photochemical processes of CD complexes,1 Differences in photochemical reactions conducted in solution and in CD complexes have been reviewed. For example, photo-Fries rearrangement of phenyl esters in solvents results in a mixture of o- and p-phenolic ketones via a radical reaction. Rearrangement of the same encapsulated ester results in exclusive rearrangement to the ortho-position (equa-... 

Photochemical reaction This term is generally used to describe a chemical reaction caused by absorption of ultraviolet, visible, or infrared radiation. There are many ground state reactions which have photochemical counterparts. Among these are photoadditions, photocycloadditions, photoeliminations, photoenolizations, photo-Fries rearrangements, photoisomerizations, photooxidations, photoreductions, photosubstitutions, etc. 

Sinha SC, Sun J, Miller GP, Wartmann M, Lemer RA. Catalytic antibody route to tbe naturally occurring epotbilones total synthesis of epothilones A-F. Chem. Eur. J. 2001 7(8) 1691—1702. Haga N, Takayanagi H. Mechanisms of the photochemical rearrangement of diphenyl ethers. J. Oig. Chem. 1996 61(2) 735—745. Dickerson TJ, Tremblay MR, Hoffman TZ, Ruiz Dl, Janda KD. Catalysis of the photo-Fries reaction antibody-mediated stabi-hzation of high eneigy states. J. Am. Chem. Soc. 2003 125(50) 15395-15401. 

It has been shown (122) that aromatic polyesters degrade by a combination of Norrish I and Norrish II photolyses, with photo-oxidation playing an important part. Aromatic esters may also undergo an important photochemical reaction, known as the photo-Fries rearrangement (123). 

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