Aryl ethers acetylation

Most of the academic studies of aryl ether acetylation are carried out in a batch reactor often in the presence of solvents, whereas in the industrial units the reactions are operated in fixed bed reactors and in the absence of solvent. 

The competition of Claisen rearrangement and [l,5]-acetyl shift upon thermal treatment of allyl aryl ether 356 resulted in a mixture of the expected Claisen product 357 and its isomer 358 (equation 129)184. It was assumed that the usual Claisen rearrangement (Section IV.E.l) resulted in an equilibrium with the intermediates of successive [3,3]-sigmatropic shifts. The cyclohexa-2,4-dienones 359 and 360 formed leave this equilibrium cycle due to enolization to form the Claisen product 357 or because of [l,5]-shift followed by enolization give the unexpected product 358 (equation 130). 

Acetylglycosyl aryl ethers, obtained by the Ferrier reaction of acetylglycals with phenols, can be de-acetylated and converted into the benzyl ethers in a one-pot reaction in the presence of a quaternary ammonium salt (see, e.g. Scheme 3.3) [30]. 

Another type of (9-glycosides (127), 12-(3 aryl ethers of dihydroartemisinin, was synthesized by a reaction of acetyl dihydroartemisinin or trifluoroacetyl dihydroartemisinin with various substituted phenols in the presence of trifluoroacetic acid. Most of these compounds were proved to have better antimalarial activity against P. berghei in mice than qinghaosu, but less activity than artemether. Unexpectedly,... 

BF3 Et20 is used for the regioselective rearrangement of polyprenyl aryl ethers to yield polyprenyl substituted phenols, e.g. coenzyme Q [92]. This reagent is used in the Fries rearrangement for example, 5-acetyl-6-hydroxycoumaran is obtained in 96 % yield from 6-acetoxycoumaran by use of this reagent (Eq. 48) [93]. 

To start our investigations, we examined the conversion of 2,3-dimethyl-2-butene (1) into 3,3,4-trimethyl-4-penten-2-one (2) as a model reaction (eq. 1). The choice of acetic anhydride as the acetylating agent was made in the light of related studies on the acylation of aryl ethers. Our work in this field had shown that acetic anhydride was the most effective reagent for the Friedel-Crafts acylation of anisole in the presence of Hp zeolite. A lower degree of conversion was achieved with acetyl chloride, while hardly any reaction occurred with ethyl acetate or acetic acid [6]. 

Acetylation of activated aryl ethers with AAN over different zeolites can be efficiently performed under relatively mild conditions. ... 

Synthetically valuable methods for the efficient acylation of aryl ethers with anhydrides over different BEA zeolites under batch conditions are also reported. Significant results are summarized in Table 4.9. The reaction can be performed without solvent, and the catalyst can be reused in the acetylation of anisole with unchanged activity for three further cycles after recovery and regeneration by heating in air at 550°C for 3 h. ... 

According to Meerwein and others,323,516 use of boron trifluoride may be valuable, since it forms well-defined molecular compounds with simple aliphatic carboxylic acids for example, aromatic and heterocyclic hydrocarbons and aryl ethers can be acetylated smoothly and in good yield by acetic anhydride and boron trifluoride.323 The preparation of boron trifluoride has been described by Krause and Nitsche and by Booth and Willson.517... 

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