And Fries rearrangement

It is evident that some leeway is available in the substituents tolerable in the m-position. The bronchodilator sulfonterol (28) is descended from this observation. Chloromethylanisole (29) is reacted with methylmereaptan to give 30, and the newly introduced group is oxidized to the methyl-sulfonyl moiety of 31 with hydrogen peroxide. Ether cleavage, acetylation and Fries rearrangement of the phenolic acetate produces 32, which is next brominated with pyrrolidinone hydrobromide tribromide and then oxidized to the glyoxal (33) with dimethyl sulfoxide. 

Harmer et al.29 have applied the sol-gel technique to prepare 1,1,2,2-tetrafluor-oethanesulfonic acid supported on silica, which proved to be an excellent catalyst for several processes such as alkylation and acylation of aromatics, isomerization, oligomerization, and Fries rearrangement. This material has activity similar to that of triflic acid but is much easier to handle. 

Zeolites H-BEA and H-Y were found to be the most active catalysts, however all catalysts readily form the phenyl benzoate (Table 4.1). In the conditions of the reaction, the formation of phenyl benzoate (PB) occurs rapidly via O-acylation of phenol. Direct C-alkylation of phenol with benzoic anhydride (B) and Fries rearrangement of phenyl benzoate results in the formation of 2- and 4-hydroxy-benzophenones (2-HPB and 4-HPB) (Scheme 4.3). 

Scheme 4.3 Reaction of phenol with benzoic anhydride O- and C-acylation and Fries rearrangement.

Solid acid catalysts are, in principle, applicable to a plethora of acid-promoted processes in organic synthesis [27-29]. These include various electrophilic aromatic substitutions, e.g. nitrations, and Friedel-Crafts alkylations and acylations, and numerous rearrangement reactions such as the Beckmann and Fries rearrangements. 

Not much attention has been directed to isomerisation and rearrangement reactions in ionic liquids. Beckmann rearrangements of ketoximes have been performed in neat ionic liquids catalysed by phosphorus(V) chlorides and oxides1 301 and Fries rearrangements of phenylbenzoates have been carried out in chloroaluminate ionic liquids with moderate to good selectivity.1 311... 

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 same resins have been used for C-acylation of phenols with anhydrides, probably via O-acylation and Fries rearrangement." However, yields are low even with 1,3-dihydroxybenzenes. 

Bolognini, M., Cavani, F, Cimini, M., Dal Pozzo, L., Maselli, L., Venerito, D., Pizzoli, F, and Veronesi, G. 2004. An environmentally friendly s)mthesis of 2,4-dihydroxybenzophenone by the single-step O-mono-benzoylation of 1,3-dihydroxybenzene (resorcinol) and Fries rearrangement of intermediate resorcinol monobenzoate the activity of acid-treated montmorillonite clay catalysts. C. R. Chim. 7 143-150. 

FRIEDEL-CRAFTS ACYLATION AND FRIES REARRANGEMENT CATALYSED... 

Friedel-Crafts acylation and Fries rearrangement catalysed by heteropoly acids... 

Preparation from 3-bromo-2-hydroxy-6-methyl-5-iso-propylbenzophenone (SMI) by reductive removal of bromine with copper powder in caproic acid at 220° for 15 min (83%) [698]. SMI was obtained from p-thymol by a three-step synthesis (bromi-nation, esterification and Fries rearrangement with titanium tetrachloride). 

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