Acyl phenols

Several methods are available to supplement the phenol alkylations described above. Primary alkylphenols can be produced using the more traditional Friedel-Crafts reaction. Thus an -butylphenol can be synthesized direcdy from a butyl haUde, phenol, and mild Lewis acid catalyst. Alternatively, butyryl chloride can be used to acylate phenol producing a butyrophenone. Reduction with hydrazine (a Wolff-Kishner reduction) generates butylphenol. 

Auch Li t hi urn a I ana t reduziert die o- und p-standig mit elektronenliefemden Gruppen (z.B. Amino, Dial-kylamino, Methoxy) substituierten aromatischen Aldehyde und Ketone mcist nur unter cncrgischen Bedingun-gen zu Kohlenwasserstoffen (z. B. in Dibutylather mehrere Tage bei 80-90°). Formyl- und Acyl-phenole werden nicht reduziert1. 

Ahnlich gute Ausheuten werden mit den Kohlensaureestem der Acyl-phenole erzielt z.B.4 ... 

A special case of aromatic acylation is the Fries rearrangement, which is the conversion of an ester of a phenol to an o-acyl phenol by a Lewis acid. 

Primary alkyl phenols have been prepared by the reduction of acyl phenols 1 by the demethylation of the corresponding ethers 12 by the diazotization of the corresponding amines 3 and by the alkali fusion of sulfonates.4 Alkyl resorcinols have been prepared by the reduction of acyl resorcinols.1 5 6 Alkyl chlororesorcinols have been prepared from the corresponding acyl chlororesorcinols by reduction.7... 

Keywords acyloxybenzene, Fries rearrangement, microwave irradiation, flava-none, o-acyl phenol... 

The base-induced transfer of the ester acyl group in an o-acylated phenol ester, which leads to a 1,3-diketone. This reaction is related to the Claisen Condensation, and proceeds through the formation of an enolate, followed by intramolecular acyl transfer. 

The Fries Rearrangement enables the preparation of acyl phenols. 

An example of more complex structural photoisomerization may be the photo-Fries rearrangement leading to a photorearrangement of O-acyl-phenols or X-acyl-anilines to give the [1,3]- or [l,5]-rearranged products, as shown in Figure 6.5. 

The enhanced acidity conferred upon / acyl phenols is sufficient for their participation in Mitsunobu displacements. Scheme 4.171 shows an example in which selective 0-benzyIation of the p-hydroxyl in the orcinol derivative 171 1 took place in preference to the o-hydroxyl.319... 

The reaction is thought to involve activated nucleophilic addition of the ketene to the aldehyde which is coordinated to the aluminum. TTie ketene is added as a gas by bubbling into a solution of the catalyst and aldehyde at -78 °C. Lower induction is observed if the aldehyde is added to a solution of the catalyst and ketene. One of the limitations of this catalyst system is that sub-stoichiometric amounts of the catalyst are not successful. With the 10 mol % of the catalyst less than 5 % yield of product was obtained. This limitation might be related to the observation that acylated phenols are observed as by-products in this reaction. The yields of the reaction are higher in dichloromethane but asymmetric induction decreases. The reaction in entry 2 of Table 5 was observed to occur in 90 % yield and in 20 % ee in dichloromethane. 

V. Snieckus and co-workers developed a new carbamoyl Baker-Venkataraman rearrangement, which allowed a general synthesis of substituted 4-hydroxycoumarins in moderate to good overall yields. The intermediate arylketones were efficiently prepared from arylcarbamates via directed ortho metallation and Negishi cross coupling. The overall sequence provided a regiospecific anionic Friedel-Crafts complement for the construction of ortho-acyl phenols and coumarins. 

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. 

Fries rearrangement Synthesis of acylated phenols from 0-acyl phenols. 180... 

Houben-Hoesch reaction. Synthesis of acyl-phenols from phenols or phenolic ethers by the action of organic nitriles in the presence of hydrochloric acid and aluminum chloride as catalyst. 

Keywords acylation, phenol, thiol, indium chloride... 

Auch Hydroxy-benzaldehyde (Bd. VI/lc, S. 1069) und Acyl-phenole (Bd. VI/lc, S. 1060) werden mit sehr guten Ausbeuten zu Alkyl-phenolen reduziert. 

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. 

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