Fries reaction

By the rearrangement of an ester of a phenol in the presence of aluminium chloride (Fries reaction), phenolic ketones are produced ... 

The mechanism of the Fries reaction is not known with certainty. One mechanism regards it as a true intramolecular rearrangement in which the acyl group migrates directly from the oxygen atom to the carbon atoms of the ring. Another scheme postulates that the ester is cleaved by the reagent... 

By the Fries reaction. This is a variant of the Friedel-Craft reaction it consists in the conversion of an ester of a phenol to the corresponding o- and p-hydroxyketone, or a mixture of both, by treatment with anhydrous aluminium chloride ... 

Synthesis of the remaining half of the molecule starts with the formation of the monomethyl ether (9) from orcinol (8). The carbon atom that is to serve as the bridge is introduced as an aldehyde by formylation with zinc cyanide and hydrochloric acid (10). The phenol is then protected as the acetate. Successive oxidation and treatment with thionyl chloride affords the protected acid chloride (11). Acylation of the free phenol group in 7 by means of 11 affords the ester, 12. The ester is then rearranged by an ortho-Fries reaction (catalyzed by either titanium... 

When acylated arylamines are photolyzed, migration of an acyl group takes place" in a process that resembles the photo-Fries reaction (11-30). 

If the photo-Fries reaction would occur via a concerted mechanism, the absence of solvent should be of minor importance for the formation of rearranged products. However, conclusive evidence supporting the radical pair mechanism arises from the experiments carried out with phenyl acetate (10) in the vapor phase. The major product in the irradiations of 10 is phenol (13), which accounts for 65% of the photoproducts. Under these conditions, less than 1% of ortho -hydroxyace-tophenone (11) appears to be formed [19,20]. Conversely, when a high cage effect is expected, as in rigid matrixes (i.e., polyethylene), the result is completely different, and phenol is practically absent from the reaction mixtures [29]. In the intermediate situation (liquid solution), both rearranged products and phenol are formed in variable amounts depending on solvent properties. These observations... 

Photolysis of 2-naphthyl thioesters in the presence of a hydrogen donor such as 1,4-cyclohexadiene yields aldehydes (80-100%) no photo-Fries reaction products have been reported [60],... 

The selectivity of the Lewis-acid-catalyzed Fries reaction is also strongly influenced by the inclusion into zeolites [284]. 

Chapter 2, by Miranda and Galinco, provides a critical survey of the photo-Fries reaction undergone by numerous aromatic esters, amides, and so forth. This chapter is a valuable companion to Chapter 5 by Fleming and Pincock, in Volume 3. Miranda and Galinco s chapter is the sixth chapter devoted to the photochemistry of aromatic compounds in this series. 

The consecutive formation of o-hydroxybenzophenone (Figure 3) occurred by Fries transposition over phenylbenzoate. In the Fries reaction catalyzed by Lewis-type systems, aimed at the synthesis of hydroxyarylketones starting from aryl esters, the mechanism can be either (i) intermolecular, in which the benzoyl cation acylates phenylbenzoate with formation of benzoylphenylbenzoate, while the Ph-O-AfCL complex generates phenol (in this case, hydroxybenzophenone is a consecutive product of phenylbenzoate transformation), or (ii) intramolecular, in which phenylbenzoate directly transforms into hydroxybenzophenone, or (iii) again intermolecular, in which however the benzoyl cation acylates the Ph-O-AfCL complex, with formation of another complex which then decomposes to yield hydroxybenzophenone (mechanism of monomolecular deacylation-acylation). Mechanisms (i) and (iii) lead preferentially to the formation of p-hydroxybenzophenone (especially at low temperature), while mechanism (ii) to the ortho isomer. In the case of the Bronsted-type catalysis with zeolites, shape-selectivity effects may favor the formation of the para isomer with respect to the ortho one (11,12). 

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). 

In contrast to If/-azepines the photolysis of N-substituted 5f/-dibenz[Z>,/]azepine under sensitized (PI12CO) conditions yields [2 + 2] cyclobutane dimers (77 R = Ac, CC Et, CONH2, COPh). The N-p- tosyl derivative, however, undergoes photo-Fries reaction to the 2-p-tosylamino derivative (74CRV101). 

Another reaction which occurs readily in solid polymers is the Fries reaction which can be observed in phenyl esters, particularly in phenyl acrylate and phenyl methacrylate polymers. The course of the reaction can be followed very... 

Fries rearrangement of aromatic formate esters suggests that phenols are the major products (.24) obtained in the reaction. As poly(p-hydroxystyrene) is remarkably clear in the deep UV, it is likely that poly(p-formyloxystyrene) will not suffer from the same problem of photostabilization upon exposure as was the case with poly (p-acetoxystyrene). This expectation was confirmed by our study of the photo-Fries reaction of p-cresyl formate no ortho rearranged product was isolated after reaction while p-cresol and a small amount of starting material were obtained. 

---