Photo-Fries rearrangement, phenyl esters

A photochemical variant, the so-called photo-Fries rearrangement, proceeds via intermediate formation of radical species. Upon irradiation the phenyl ester molecules (1) are promoted into an excited state 11. By homolytic bond cleavage the radical-pair 12 is formed that reacts to the semiquinone 13, which in turn tautomerizes to the p-acylphenol 3. The corresponding ort/zo-derivative is formed in an analogous way ... 

The radiation induced side-chain modification of polymers containing pendant phenyl ester groups has been the object of several studies as some undergo a photo-Fries rearrangement (JJ while others such as... 

From the point of view of quantum yields calculation, photo-Fries rearrangement, including phenol and products formation, represents a photoreaction (expressed by Eq. 3) in which all products absorb intensively in the absorption region of the starting phenyl ester A. 

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-... 

The photolysis of phenyl benzoate 8.88 is an example of the photo-Fries rearrangement, in which the acyl radical is created close to a phenoxy radical 8.89. The C—O bond is weakened by the presence of an electron in the n orbital of the ester conjugated system. The radical coupling then shows the usual selectivity for C—C bond formation, with the para selectivity in line with the coefficients of the SOMO of the phenoxy radical (see page 291). 

The photoreactivity of phenyl benzoates in which the para positions of both rings are substituted has been examined in liquid crystalline media and compared with the results obtained in isotropic solution.The photoreactivity of phenyl esters of cyclohexane carboxylic acids in which the para position of the phenyl ring and the 4-position of the cyclohexane ring are substituted were also studied under the same conditions.The products were not identified but were assumed to arise from photo-Fries rearrangement based upon the development of absorption in the ultra-violet spectrum assignable to ortho-hydroxyphenyl ketones. The relative quantum yields of the rearrangements were correlated with the viscosity and order of the liquid crystalline phase. 

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. 

Photorearrangements. The photo-Fries rearrangement of phenyl esters (91a) in solution was the first photochemical example of stereoselectivity driven by / -CD. 

The light-induced rearrangement of phenyl esters 36 into hydroxy aryl ketones 37 and 38 is called the photo- Fries rearrangement [41]. Because of low yields, this procedure has little commercial importance. The reaction is usually carried out in an aprotic solvent and involves a radical mechanism by the homolytic cleavage of the (9-acyl bond from its singlet excited state [41]. 

Obtained (poor yields) by photo-Fries rearrangement of two substituted phenyl esters in C(CH3)3 benzene [154],M-tert-butyl-2-chlorophenyl benzoate (7%) ... 

The photo-Fries rearrangement was described as being a rearrangement of phenyl ester entities with their transformation in ortho hydroxy ketones and para hydroxy ketones. The reaction occurs in three steps formation of two radicals, recombination and hydrogen extraction [13-15]. The general implied reactions are depicted in Scheme 5 [2]. 

Photo-Fries rearrangement of anilides obeys the same mechanism as photo-Fries rearrangement of phenyl esters. The only difference is the replacement of bridging oxygen by Nitrogen. 

Photodecarboxylation in the presence of photocatalysts such as TiOj has also been studied. For example, the photodegradation of (4-chloro-2-methylphenoxy)acetic acid, a herbicide, in an aqueous solution of TiOj involves elimination of carbon dioxide from the initially formed radical species on the catalyst surface. The templating of carboxyHc acids with polyethylene films has been found to enhance the photodecarboxylation at the expense of the photo-Fries rearrangement in simple aryl esters such as phenyl and 1-naphthyl esters." ... 

Other heterocyclic systems readily undergoing photo-Fries or related rearrangements include O-benzoyl- and N-benzoyl derivatives of hydroxypyridines39 and aminopyridines,40 respectively, the phenyl esters of a variety of heteroaromatic acids,41 certain aryloxy-l,3,5-triazines,42 and 1-benzoylindole.43 The -azepine... 

---