Aromatic ethers acylation

Whilst bismuth (III) chloride is an efficient catalyst for the aromatic ether acylation by acid chlorides or anhydrides, it is not strong enough to carry out the acylation of non activated aromatics. However, the potential of using a wide range of Bi (III) salts as catalysts (ref. 41), in particular the oxide, the oxychloride and the carboxylates, all non hygroscopic compounds, offers advantages, and is indicative of the great versatility of Bi (III) derivatives. Moreover, the Bi salts obtained after hydrolytic workup are directly reusable. 

Like other aromatic compounds, aromatic ethers can undergo substitution in the aromatic ring with electrophilic reagents, eg, nitration, halogenation, and sulfonation. They also undergo Eriedel-Crafts (qv) alkylation and acylation. 

H-Bond Acceptor (HBA) Acyl chlorides Acyl fluorides Hetero nitrogen aromatics Hetero oj gen aromatics Tertiary amides Tertiary amines Other nitriles Other nitros Isocyanates Peroxides Aldehydes Anhydrides Cyclo ketones Ahphatic ketones Esters Ethers Aromatic esters Aromatic nitriles Aromatic ethers Sulfones Sulfolanes... 

Friedel-Crafts acylation of aromatic ethers has been performed in the presence of a variety of metal chlorides and oxides (FeCl3, ZnCl2, A1C13, Fe203, Fe304, etc.) but without temperature control [52], Scheme 10.8. 

Compounds 1 and 2 were identified by FTIR and 13C-NMR. The 13C proton decoupled spectra for 1 and 2 are dominated by signals ranging from 62 to 195 ppm. The 13C chemical shift assignments were made based on comparisons with 4,4 -(hexafluoroisopropylidene)diphenol and from calculations based on substituted benzenes and naphthalenes.15 The 13C-NMR spectrum clearly showed that the Friedel-Crafts acylation of 1 by 4-fluorobenzoyl chloride yielded the 1,4-addition product exclusively. The 13C chemical shifts for 2 are listed in Table 8.1. The key structural features in the FTIR spectrum of2 include the following absorptions aromatic C-H, 3074 cnr1, ketone C=0, 1658 cm-1, aromatic ether Ar—0—Ar, 1245 cm-1, and C—F, 1175 cm-1. 

Polyphosphoric acid has also been used to effect both acylation of aromatic ethers and subsequent ring closure (74IJC474). 

Also, Marquie and co-workers have conducted Friedel-Crafts reactions on a large laboratory scale via a continuous flow process126. They reported the acylation of aromatic ethers and sulphonylation of mesitylene, isolating up to 300 g and 250 g of product, respectively (Schemes 9.13 and 9.14). 

The acylation of aromatic ethers by acyl chlorides is highly regioselective in the presence of 10 mol% Sml3.53 Some aromatic compounds are efficiently acylated by acid anhydrides catalysed by niobium pentachloride with silver perchlorate.54 Arenes of a range of reactivity are acylated by acetic anhydride in a fluorous biphasic system catalysed by Hfps SCLCgFn L (1 mol%)55 The catalyst is easily recoverable and can usually be used again without decrease in activity. 

In zeolite-catalysed acylation of aromatic ethers, zeolites have two advantages with respect to benzene and alkylbenzene acylation ... 

Acylation of aromatic ethers yields the corresponding keto ethers. Typical examples are found in the conversion of anisole with aluminum chloride and appropriate acyl halide to p-methoxybutyrophenone (85%) and p-methoxyphenyl benzyl ketone (84%). Mild catalysts like iodine and phosphorus pentoxide are also effective. 

Ranu, B. C., Ghosh, K., Jana, U. Simple and Improved Procedure for Regioselective Acylation of Aromatic Ethers with Carboxylic Acids on the Solid Surface of Alumina in the Presence of Trifluoroacetic Anhydride. J. Org. Chem. 1996, 61, 9546-9547. 

Bismuth(lll) salts such as BiCls, BiBrj, Bi(OCOR)3, and Bi (OTf), [166] have been widely used as Lewis acid catalysts to mediate C-C bond formation. Bi (OTf) 3, Bi2O3, and BiCl, catalyze Friedel-Crafts acylation with acyl chlorides or acid anhydrides [167]. Both electron-rich and electron-deficient arenes are acylated in high yields under catalysis by Bi(OTf)3 (Scheme 14.82). Under microwave irradiation the catalytic activity of BiX3 (X = C1, OTf) in the acylation of aromatic ethers is enhanced [168]. The N-acyl group of p-substituted anilides migrates to the ortho position of the aromatic nucleus under BiCls catalysis [169]. Treatment of 2,3-dichloroanisole with the ethyl glyoxylate polymer in the presence of a catalytic amount of Bi(OTf)3 affords an a,a-diarylacetic acid ester quantitatively (Scheme 14.83) [170]. 

Friedel-Crafts Acylation of Aromatic Ethers Using Zeolites... 

An impressive number of papers and books has been published and numerous patents have been registered on the aq lation of aromatic compounds over solid catalysts. Recently Sartori and Maggi [1] have written an excellent review with 267 references on the use of solid catalysts in Friedel-Crafts acylation. In one section of this review, namely acylation of aromatic ethers or thioethers, the authors report work on acylation by solid catalysts such as zeolites, clays, metal oxides, acid-treated metal oxides, heteropolyacids or Nafion. When examining in details these results, it appeared very difficult for us to build upon these experimental results as the reaction conditions differ drastically from one paper to the next. This prompted us to reinvestigate the scope and limitations of the Friedel-Crafts acylation using heterogeneous solids as catalysts, trying as much as we could to rationalize the observed effects. 

Speciality and fine chemicals Chapter 14, Friedel-Crafts acylation of aromatic ethers Chapter 15, the production of nicotinates Chapter 16, production of intermediate for resmethrins. 

Acylation of Aromatic Ethers. A simple and improved procedure for regioselec-tive acylation of aromatic ethers with carboxylic acids on alumina in the presence of trifluoroacetic anhydride has been described by Ranu et al. [Eq. (21)]... 

Other recent works concerning the catalytic acylation of aromatic ethers concern ... 

BISMUTH HU) SALTS IN THE FRIEDEL-CRAFTS ACYLATION OF AROMATIC ETHERS... 

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