Phenolic esters rearrangement

FRIEDLANDER Quinoline synthesis t32 FRIES Phenol ester rearrangement 133 FRITSCH. BUTTENBERG - WIECHELL Acetylene synthesis 134... 

FRIES Phenol Ester Rearrangement Rearrangement of phenol esters to o or p ketophenols Lewis acid catalyzed... 

Subsequent work by Ruwet and co-workers proposed something similar to the proposal 1 mechanism, albeit they did not think that the phenolate ester rearranged via a Fries reaction. Ruwet and co-workers studied the heteroatom displacement of the phenol oxygen with S and Se. They suggested that the first step could be esterification followed by nucleophilic attack of the phenol on the more electrophilic carbon of the ketone moiety. Ruwet and co-workers prepared the phenolate 22a-c from the diketene and the corresponding phenols la-c. Treatment of la-c (X = O, S or Se) and diketene 21 with PPA (polyphosphoric acid) did indeed provide the chromone 23a-c in about 40% yield.This was the first reported use of PPA for this transformation. 

The Eries rearrangement of phenol esters gives a mixture of 2- and 4-acylphenols (56). The reaction is cataly2ed by Lewis acids such as aluminum chloride or by Brmnsted acids like hydrogen fluoride. This reaction is used in the production of 4-hydroxyacetophenone [99-93-4] a raw material for... 

Phenolic esters (1) of aliphatic and aromatic carboxylic acids, when treated with a Lewis acid as catalyst, do undergo a rearrangement reaction to yield ortho- and para-acylphenols 2 and 4 respectively. This Fries rearrangement reaction is an important method for the synthesis of hydroxyaryl ketones. 

Employing this method, enantioenriched phenol esters 68, amides 69, and carbamates 70 (after Curtius rearrangement of the intermediate acyl azide) were prepared in yields often greater than 90% with ee-values reaching up to 97% (generally 80-95%, see Fig. 37). 

Fries rearrangement org chem The conversion of a phenolic ester into the corresponding 0- and p-hydroxyketone by treatment with catalysts of the type of aluminum chloride. frez re a ranj-mant)... 

Lewis acid-catalyzed rearrangement of phenol esters and lactams to 2- or 4-ketophenols. Also known as the Fries-Finck rearrangement. 

Fries, K. Finck, G. Ber. Dtsch. Chem. Ges. 1908, 41, 4271. Karl Theophil Fries (1875-1962) was born in Kiedrich near Wiesbaden on the Rhine. He earned his doctorate under Theodor Zincke. Although G. Finck co-discovered the rearrangement of phenolic esters, somehow his name has been forgotten by history. In all fairness, the Fries rearrangement should really be the Fries-Finck rearrangement. 

The PFR of phenolic esters is by far the best known of this group of rearrangements. The PFR of phenyl acetate (Scheme 3) is the prototype of all of them. 

Phenol esters of a,(3-unsaturated carboxylic acids have an interesting reactivity due to the synthetic utility of the resulting hydroxychalcones (Scheme 19). This aspect will be illustrated in Section IV. However, from the basic point of view, it is worth mentioning that the cis or trans configuration of the olefinic part of the acyl moiety can have a marked influence on the photochemical reactivity of the ester. When para-methoxyphenyl fumarates are irradiated, the normal ortho-rearranged products are obtained. By contrast, irradiation of para-me-thoxyphenyl maleates does not lead to rearrangement. Instead, cyclization products are obtained (Scheme 20). 

Fries rearrangement of phenolic esters to phenolic ketones (Problem 19.16). 

Reduction of nitro compounds 1-30 Rearrangement of phenolic esters... 

The Fries rearrangement of phenol esters gives a mixture of 2- and 4-acylphenols. Similarly, enol esters undergo rearrangement to give the corresponding 1,2-di ketones. 

Fries rearrangement—that is, the transformation of phenolic esters to isomeric hydroxyphenyl ketones—is related to Friedel-Crafts acylations.392,393 Olah et al.394 have found a convenient way to perform the Fries rearrangement of a variety of substituted phenolic esters in the presence of Nafion-H in nitrobenzene as solvent [Eq. (5.153)]. A catalytic amount of Nafion-H is satisfactory, and the catalyst can be recycled. In contrast, Nafion-silica nanocomposites, in general, exhibit low activities in the Fries rearrangement of phenyl acetate to yield isomeric hydroxyacetophe-nones.239,395 In a recent study, BF3-H20 was found to be highly efficient under mild conditions (80°C, 1 h) to transform phenolic esters of aliphatic and aromatic carboxylic acids to ketones (71-99% yields).396 In most cases the para-hydroxyphenyl isomers are formed with high (up to 94%) selectivity. 

Phenolic ketones may be prepared by the Hoesch acylation reaction, which may be regarded as an extension of the Gattermann aldehyde synthesis (Section 6.10.1, p. 990). The procedure involves reaction of a nitrile with a phenol (or phenolic ether) in the presence of zinc chloride and hydrogen chloride best results are usually obtained with polyhydric phenols or their ethers, as for example in the preparation of phloroacetophenone (Expt 6.125). The formation of phenolic ketones by means of the Fries rearrangement of phenolic esters with aluminium chloride is discussed on p. 976. 

When treated with acid chlorides and acid anhydrides, phenols form esters. Under Friedel-Crafts conditions, phenolic esters undergo a Fries rearrangement in which the acyl group migrates to the 2- and 4-positions. Thus, treatment of the ester 11 with aluminium chloride in an inert solvent gives a mixture of 2- and 4-hydroxyacetophenones [(hydroxy-phenyl)ethanones] C-acylation has occurred (Scheme 4.7). The two isomers are separable and this is a useful method for the production of phenolic ketones. The mechanism remains uncertain, but it would appear that the acylium ion (RCO" ) is generated and that a Friedel-Crafts mechanism operates. 

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