Photo-Fries rearrangement esters

Sulfones from sulfonic acid esters Photo-Fries rearrangement OSO2R C SOjR... 

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 ... 

A variant of Method B is the cyclization of the phenolic 2-(chloroacetamido)benzophenones 9, produced by photo-Fries rearrangement (see Houben-Weyl, Vol. 7/2a, p 1148 ff) of the esters 8, with ammonia via the corresponding iodoacetyl compounds.195... 

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... 

Photo-Fries Rearrangement of Styrylpyridine Based Ester and Carbonate-UV-Spectroscopic Studies... 

The photo-Fries rearrangement of aryl hydrogen (or methyl) succinates 267 leads to 4-(2-hydroxyaryl)-4-oxobutanoic acids (or methyl esters 268), which are readily cyclized to 5-(2-acetoxyaryl)-2(3//)-furanones (269) (Scheme 68). [189-191] Photolysis of 269 [191] or the analogous open-chain enol acetates [192,193] leads to chromones. 

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. 

Ortho- and para-rearrangement and phenol formation on uv-irradiation of aryl esters are accompanied in several cases by decarboxylation,37,60,62,64,80,81 represented for 3,5-di-t-butylphenyl benzoate by the equation 118 -> 119-122. It was shown that this reaction cannot be sensitized,64 but the dramatic differences in product distribution could be observed by changing of the solvent.60,84 The results in Table VI indicate that in polar solvents the decarboxylation process is minimized while the formation of the photo-Fries rearrangement 119 is enhanced. The reverse appears to be true when nonpolar ethereal solvents are used. A considerable amount of biaryls are formed, and hence this reaction may prove useful for the preparation of biaryls and alkylary Is. 

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. 

The exact calculation of quantum yields is possible only (1) if products Bi to B are photochemically very stable when compared with A, and (2) if the products do not exhibit any influence upon the excited state of compound A. Both these conditions are satisfactorily fulfilled in the photo-Fries rearrangement, particularly for small conversions of the ester (up to 20% conversion of A). 

Cui and Weiss reported the photo-Fries rearrangements of 2-naphthyl myristate and 2-naphthyl acetate (Fig. 35) in unstretched and stretched low-density polyethylene films [116]. It was argued that the radical pair generated by irradiation is held in a cavity shaped like the starting ester and whose walls relax more slowly than the radicals recombine. The preferred solution product is too different in shape from the starting ester to be formed. 

Another example of the effect of confined medium is found during photo-Fries rearrangement of naphthyl esters in zeolites [103,104]. Upon photolysis in isotropic solution 1-naphthyl benzoate undergoes the photo-Fries rearrangement to yield both ortho (2-) and para (4-) phenolic ketones (Sch. 4). When this ester is included in NaY zeolite and irradiated the main product (96%) is the ortho isomer. This remarkable ortho-selectivity within zeolites has been rationalized on the basis of interactions of the reactant 1-naphthyl benzoate and intermediate radicals with the sodium ion. Due to restrictions imposed by the medium the benzoyl radical, once formed, is compelled to react only with the accessible ortho position. 

The photo-Fries rearrangement of polymers such as 1 leads to yellowing, an undesirable behavior for many potential applications. The photochemistry of analogous MCLC polymers has been reported [30] in which the alkoxyphenyl ester groups of 1 have been replaced by 4,4 -franj-disubstituted cyclohexyl... 

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 enol ester (307) undergoes a photo-Fries rearrangement, giving a (3-diketone, isolated in its enolic form (308).245... 

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 Fries rearrangement proceeds via ionic intermediates but the exact mechanistic pathway (whether it is inter- or intramolecular) is still under debate. There are many reports in the literature that present evidence to support either of the pathways, but it appears that the exact route depends on the structure of the substrates and the reaction conditions. The scheme depicts the formation of an ortho-acylated phenol from a substituted phenolic ester in the presence of aluminum trihalide catalyst. The photo-Fries rearrangement proceeds via radical intermediates. ... 

Research in the laboratory of P. Magnus showed that the macrocyclic skeleton of diazonamide could be synthesized with the use of macroiactonization followed by a photo-Fries rearrangement. First, the aromatic carboxylic acid and the phenol were coupled with EDCI to form the macrolactone (phenolic ester), which was then exposed to light at high-dilution to cleanly afford the macrocyclic ortho-acylated phenol skeleton of diazonamide. 

The Fries rearrangement can also be carried out in the absence of a catalyst by photolysis. This reaction, known as the photo-Fries rearrangement, is predominantly an intramolecular free-radical process formed by the initial photolysis of the ester . Both ortho and para migrations are observed. The product distribution is strongly dependent... 

Arenes of the type Ar-X-Y in vbich the X-Y bond is readily cleaved homolytically undergo facile lateral-nuclear rearrangement. The archetypal example of this process is the photo-Fries rearrangement which occurs with aryl esters and anilides and several reports of these reactions have appeared within the review period. Several... 

The hydroxylated copolymers, poly(acenaphthylene-co-vinyl alcohol), were reacted with the following acyl chlorides 1-naphthoyl, 2-naphthoyl, benzoyl and cinnamoyl. The latter polymers contain an ester group as a spacer between the main chain and one of the fluorophores. The choice of an ester group as a connecting unit between the polymer chain and fluorophore is probably a poor one since it is known that carbonyl groups easily form triplets and photo-Fries rearrangements can occur (2). 

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. 

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