Acylation of arenes

Klumpp, D. A. Rendy, R. Zhang, Y. Gomez, A. McElrea, A. Dicationic Intermediates Involving Protonated Amides Dual Modes of Reactivity Including the Acylation of Arenes. Org. Lett. 2004, 6,1789-1792. 

Friedel-Crafts acylations of arenes with RCOCl or anhydrides (RC—O—CR) in the presence of AICI3 give good yields of ketones. 

Acylation of arenes. These mixed anhydrides have been used Tor acylation of arenes. However these reagents are sensitive to moisture and tend to disproportionate. One solution is to generate the reagents in situ. Thus acyl trifluoro-acetates can be generated in the presence of the arene from a carboxylic acid, TFAA, and 85% phosphoric acid (as catalyst) in CHjCN. Ketones of the type O II... 

Aldehydes and ketones are usually prepared on insoluble supports by the acylation of arenes, C,H-acidic compounds, or organometallic reagents. Alcohols or other substrates can also be converted into carbonyl compounds by oxidation (Figure 12.1). Linkers that enable the generation of aldehydes and ketones upon cleavage from a support are considered in Section 3.14. 

Formaldehyde, acetaldehyde, and acetone are important commercial chemicals, synthesized by special methods. In the laboratory, aldehydes and ketones are most commonly prepared by oxidizing alcohols, but they can also be prepared by hydrating alkynes and by Friedel-Crafts acylation of arenes. Aldehydes and ketones occur widely in nature (see Figure 9.1). 

A complex of SbCls and benzyltriethylammonium chloride, which is insensitive to air and moisture, catalyzes the Friedel-Crafts acylation of arenes with acyl chlorides and sulfonyl chlorides (Equation (36)).69 The Diels-Alder reaction of toluquinone with 1,3-dienes is catalyzed by SbCl5 with high regioselectivity (Equation (37)).70... 

Acylation of Water (Hydrolysis) with Imidothioates, Thioorthoesters and Ketene S,S-Acetals Acylation of Arenes and Carbanions under Formation of Carbon-Carbon Bonds... 

S Acylation of Arenes and Carbanions under Formation of Carbon-Carbon Bonds... 

Friedel-Crafts acylation of arenes (c/. Volume 2, Chapter 3.1) can be achieved with 5-aryl or 5-n-alkyl chlorothioformates in good to moderate yields (equation 30). ... 

The A-Boc group is rapidly removed on reaction with AlClj under microwave irradiation. Friedel-Crafts reactions. Both alkylation and acylation of arenes can be performed without solvent, by thoroughly grinding the reagents in an agate mortar and pestle at room temperature. (This technique is also applicable to Beckmann rearrangement of oximes in nearly quantitative yields. )... 

Benzoylation under Friedel-Crafts acylation is an important process for the preparation of many industrially valuable chemicals. However, like the acetylation, the use of conventional Lewis acids, for example, AICI3, ZnCl2, and so on, in the homogeneous Friedel-Crafts acylation of arenes entails problems of materials due to corrosion work up and effluent issues. Thus, for benzoylation, as with acetylation, the use of heterogeneous catalysts seems to be an interesting alternative technique to the homogeneous reaction. 

The whole argument is organized in four sections stoichiometric acylations, catalytic homogeneous acylations, catalytic heterogeneous acylations, and phenol acylations. It is structured according to the role played by the catalyst in the activation of reagents as well as in the different modes of regioselectivity encountered in the acylation of arenes, aromatic ethers, and phenols. 

The acylation of arenes with succinic and phthalic anhydrides in a chloroaluminate ionic liquid gives the corresponding ketoacids in good yields (50%-95%). The system follows a fypical elecfrophilic behavior, and lower yields are achieved with election-poor aromatics. ... 

Different patents have been registered concerning the preparation of specific aryl ketones by Friedel-Crafts acylation of convenient aromatic substrates in the presence of variable amounts of both Bronsted and Lewis acids. As an example, a large number of aryl ketones was efficiently synthesized through acylation of arenes with acyl chlorides in methylene chloride and in the presence of a mixture of aluminum chloride and lithium chloride as the catalyst. Some synthetic results are reported in Table 2.3. 

Galli, C. 1979. Acylation of arenes and heteroarenes with in situ generated acyl trifluoroacetates. Synthesis 303-304. 

Late-transition metal salts have been utilized as catalysts to promote Friedel-Crafts acylation of arenes and heteroarenes with anhydrides. A mismatch between their soft metal center and the hard carbonyl oxygen atoms of the products avoids the formation of a kinetically inert complex and results in catalytic turnovers. Although late-transition metal salts exhibit, a priori, rather poor Lewis acidity, sufficient reactivity can be gained by rendering them cationic. The acylation of variously substituted... 

Ytterbium(lll) tris(perfluoroalkanesulfonyl)methides 34 are effective catalysts (10% mol) for the Friedel-Crafts acylation of arenes with anhydrides. Compounds 34 can be prepared as described in Scheme 3.7. Trimethylsilylmethyl lithium 31 is reacted with commercially available per-fluoroalkanesulfonyl fluorides, giving intermediates 32 that can similarly produce tris-perfluoroalkanesulfonyl derivatives 33. These compounds are converted into the catalysts 34 by reaction with ytterbium oxide. It is shown that the highly fluorinated catalyst (34, Ri = C5F13, = C8F17) (10% mol)... 

Bromopentacarbonylrhenium(I) [ReBr(CO)5] promotes the Friedel-Crafts acylation of arenes with acyl chlorides. Toluene rmdergoes benzoy-lation with BC in the presence of the rhenium-based catalyst (0.1% mol), affording a mixture of ortho-, meta-, and para-methylbenzophenones in 91% yield (11 4 85 molar ratio). The yield decreases to 72% when using the same catalyst in a lower amount (0.01% mol). The process can be applied to different acyl chlorides, giving the corresponding ketones a satisfactory to high yield (Table 3.17). 

Kusama, H. and Narasaka, K. 1995. Friedel-Crafts acylation of arenes catalyzed by bromopentacarbonylrhenium(i). Bull Chem. Soc. Jpn. 68 2379-2383. 

Thanks to their low cost and easy availability, many metal-exchanged clays have been patented as efficient solid catalysts in Friedel-Crafts acylation reactions. A great number of arylketones is prepared by electrophilic acylation of arenes with anhydrides in the presence of ion-exchanged clays at 150°C-250°C. Thus, for example, aluminum-enriched mica promotes the reaction of BAN with mcto-xylene at reflux for 4 h in 99% yield. 

The use of HPAs and multicomponenf polyoxometalates as catalysts in liquid-phase reactions was reviewed by Kozhevnikov. Moreover, an interesting minireview was published concerning the Friedel-Crafts acylation of arenes and the Fries rearrangement catalyzed by HPA-based solid acids. The results show that HPA-based solid acids, including bulk and supported heteropoly acids as well as heteropoly acid salts, are efficient and environmentally friendly catalysis for all reacfions analyzed. 

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. 

Friedel-Crafts acylation. 1 lyzes the acylation of arenes at roo benzene — acetophenone)... 

---