Aromatic compounds, with acyl halides

Ferrocene behaves in many respects like an aromatic electron-rich organic compound which is activated toward electrophilic reactions.In Friedel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is lO times more reactive than benzene and gives yields over 80%. However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious. 

Because acylation of an aromatic ring can be accomplished without rearrangement it is frequently used as the first step m a procedure for the alkylation of aromatic compounds by acylation-reduction As we saw m Section 12 6 Friedel-Crafts alkylation of ben zene with primary alkyl halides normally yields products having rearranged alkyl groups as substituents When a compound of the type ArCH2R is desired a two step sequence IS used m which the first step is a Friedel-Crafts acylation... 

Friedel-Crafts acylation reactions usually involve the interaction of an aromatic compound with an acyl halide or anhydride in the presence of a catalyst, to form a carbon-carbon bond [74, 75]. As the product of an acylation reaction is less reactive than its starting material, monoacylation usually occurs. The catalyst in the reaction is not a true catalyst, as it is often (but not always) required in stoichiometric quantities. For Friedel-Crafts acylation reactions in chloroaluminate(III) ionic liquids or molten salts, the ketone product of an acylation reaction forms a strong complex with the ionic liquid, and separation of the product from the ionic liquid can be extremely difficult. The products are usually isolated by quenching the ionic liquid in water. Current research is moving towards finding genuine catalysts for this reaction, some of which are described in this section. 

Diaryl sulfones can be formed by treatment of aromatic compounds with aryl sulfonyl chlorides and a Friedel-Crafts catalyst. This reaction is analogous to Friedel-Crafts acylation with carboxylic acid halides (11-14). In a better procedure, the aromatic compound is treated with an aryl sulfonic acid and P2O5 in polypho-sphoric acid. Still another method uses an arylsulfonic trifluoromethanesulfonic anhydride (ArS020S02CF3) (generated in situ from ArS02Br and CF3S03Ag) without a catalyst. ... 

The alkylation of aromatic compounds using alkyl halides and a Lewis acid only requires a small amount of catalyst. Because Lewis acids form complexes with carbonyl compounds, the Lewis acids are effectively removed from the reagent system to the extent that product is formed. Although an equilibrium exists between the product complex and free Lewis acid, there is an apparent inhibition of formation of the acylating species. The net effect is that the amount of the ketone that is formed is normally proportional to the molar quantity of catalyst added. In reactions using acyl halides, completion occurs when slightly more than 1 mol of catalyst is used. When using a carboxylic anhydride, an excess over 2 mol of catalyst will usually be required because the other product, a carboxylic acid, will also complex with the Lewis acid. 

Ketone synthesis. Ketones can be prepared in 65-85% yield by the reaction of aromatic or aliphatic acyl halides with diaryl- or dialkylmercury(II) compounds in HMPT with this palladium complex as catalyst. ... 

The Friedel—Crafts acylation reaction is often carried out by treating the aromatic compound with an acyl halide (often an acyl chloride). Unless the aromatic compound is one that is highly reactive, the reaction requires the addition of at least one equivalent of a Lewis acid (such as AICI3) as well. The product of the reaction is an aryl ketone ... 

Metal triflates that can be easily prepared from metal halides and triflic acid at -78°C [14] show several unique properties compared with the corresponding metal halides. The use of bismuth(III) triflate allows for acylation of both activated and deactivated aromatic compounds with anhydrides and acyl chlorides [15]. Thus, the acylation of deactivated aromatics such as trifluoromethoxyben-zene, fluorobenzene, and chlorobenzene can be achieved in high yields with benzoyl chloride in the presence of bismuth(III) triflate (10% mol) without solvent. The />ara-acylation product is the most abundant in all cases (trifluoromethoxybenzene 87% yield, ortho.para 4 96 fluorobenzene 86% yield, orthoipara 0 100 chlorobenzene 89% yield, ortho para 13 87). 

Graphite can promote the Friedel-Crafts acylation reaction of active aromatic compounds such as anisoles and polymethylbenzenes with acyl halides to afford the corresponding aromatic ketones [101]. In a typical experiment, graphite is added to a mixture of anisole and benzoyl bromide in benzene, and the mixture is heated under reflux for 8h to afford para-methoxybenzophenone in 80% yield. Different acyl halides and several anisoles and polymethylbenzenes are utilized to give the corresponding products in high yields (60-92%). 

Aromatic compounds with nitro groups ortho to the alkyne have been converted into indoles (eq 9). Alkynyl ketones have been prepared from either the corresponding acyl halides or by carbonylative ethynylation of vinyl halides and triflates with TMSA. 

Acyl halides, both aliphatic and aromatic, react with the sodium derivative, but the product depends largely on the solvent used. Thus acetyl chloride reacts with the sodium derivative (E) suspended in ether to give mainly the C-derivative (t) and in pyridine solution to give chiefly the O-derivative (2). These isomeric compounds can be readily distinguished, because the C-derivative (1) can still by enolisation act as a weak acid and is therefore... 

Appaiendy a molai equivalent of catalyst (AlCl ) combines with the acyl halide, giving a 1 1 addition compound, which then acts as the active acylating agent. Reaction with aromatics gives the AlCl complex of the product ketone hberating HX ... 

---