Naphthyl esters, rearrangement

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. 

Friedel-Crafts reactions. For alkylation of arenes with secondary alkyl triflates at 80 the Sc(OTf)j catalyst can be reused without significant loss of activity. Direct acylation of 1-naphthol at C-2 and Fries rearrangement of 1-naphthyl esters are effected by... 

The Fries rearrangement of phenyl- and 1-naphthyl esters can be efficiently performed in the presence of hafnium triflate. The method is based on the one previously described for the Friedel-Crafts acylation of arenes with acyl chlorides. The reaction occurs in toluene-nitromethane mixtures at 100°C for 6 h. Several examples of this Fries isomerization with synthetic application are reported in Table 5.5. In all cases, complete regioselectivity is obtained, and 2-acylated phenol or naphthol derivatives are isolated in good yields. 

Results of the Fries rearrangement of 1-naphthyl esters promoted by scandium triflate (5% mol) are reported in Table 5.6. The reaction proceeds smoothly in toluene at 100°C for 6 h to produce l-hydroxy-2-naphthyl ketones in high selectivity. The yields obtained are much higher than those achieved in the stoichiometric aluminum-chloride-promoted reactions. ... 

Table 5.6 Scandium-triflate-promoted Fries rearrangement of naphthyl esters...

Table 5.14 Clay-promoted Fries rearrangement of phenyl and 1-naphthyl esters at 140°C for 5 h...

Further detailed studies confirm the impressive role played by the support in the photo-Fries rearrangement of 1-naphthyl esters. Indeed, l-hydroxy-2-acylnaphthols are obtained in 93%-99% yield upon irradiation (>300 nm) of different naphthyl esters adsorbed on LiY, NaY, and KY. 

The archetypal photochemical lateral-nuclear rearrangement in aromatic compounds is the photo-Fries rearrangement, and a relatively simple example is reported in which /Mjhlorophenyl salicylate (189) gives 5-chloro-2,2 -dihydroxybenzophenone. Use is made of the photo-Fries rearrangertient of 1-naphthyl esters (190) in the regioselective synthesis of tricyclic analogues of... 

Serum albumins have been employed as hosts for the photo-Fries rearrangement of 4-methoxy-l-naphthyl esters, at site I (acetate) and site II (monoglutarate) of the proteins. A species- and site-dependent quantum yield of product formation is observed the best results are obtained within site I of bovine serum albumin. ... 

The PFR of phenyl esters [106-110], anilides [108, 111, 112], and sulfonyl anilides [113] has been thoroughly investigated in the presence of cyclodextrins. In general, complexation within this hydrophobic microenvironment favors formation of the ort/jo-rearranged isomer. Likewise, in the case of 1-naphthyl esters [114-116], the selectivity toward 2-acylnaphthols increases when the reaction is performed with the inclusion complexes. 

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. 

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." ... 

The esters of naphthol have also been reported to undergo photochemical rearrangement. 1-Naphthyl acetate (60) [28,39,50] gives 2- and 4-acetyl-1-naph-... 

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. 

DL-a-acetamido-P-hydroxy-p-nitropropiophenone has been prepared from L-(+)-threo-(p-nitrophenyl)-2-aminopropan-l,3-diol and acetic anhydride followed by photooxidation in the presence of acidic KBrOs and HBr. Photosensitized electron transfer reactions of tri-1-naphthyl phosphate and di-1-naphthyl methyl phosphate using 9,10-dicyanoanthracene are reported to lead to the formation of 1,1 -binaphthyl, but no reaction occurs for mono-1-naphthyl and di- or tri-phenyl esters. Irradiation of bis(3,4-methylenedioxyphenyl) methylphosphonate in the presence of DCA induces single electron oxidation followed by intramolecular rearrangement and gives 2-(3,4-methylenedioxyphenyl)-3,4-methylenedioxy-phenyl methylphosponate. ... 

Inorganic mesoporous materials such as zeolites have also served as hosts for aromatic esters whose irradiation leads to changes in the selectivity of the photoproducts ortho preference) in comparison with the rearrangement in homogeneous media., - Finally, the photochemical Fries rearrangement of naphthyl acetate has shown the occurrence of solvent-solute clustering in supercritical carbon dioxide. " ... 

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