Friedel-Crafts acylation with sulfonic anhydrides

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. ... 

Proton acids can be used as catalysts when the reagent is a carboxylic acid. The mixed carboxylic sulfonic anhydrides RCOOSO2CF3 are extremely reactive acylating agents and can smoothly acylate benzene without a catalyst.265 With active substrates (e.g., aryl ethers, fused-ring systems, thiophenes), Friedel-Crafts acylation can be carried out with very small amounts of catalyst, often just a trace, or even sometimes with no catalyst at all. Ferric chloride, iodine, zinc chloride, and iron are the most common catalysts when the reactions is carried out in this manner.266... 

Friedel-Crafts Acylation of Cedrene. Let us now look in a little more detail at the Friedel-Crafts acylation of cedrene. This reaction can be carried out using acetic acid or acetic anhydride with an acid catalyst such as formic acid, phosphoric acid or sulfuric acid. The species which attacks the double bond of cedrene is the protonated acid or anhydride molecule. When sulfuric acid is used as a catalyst with acetic anhydride as the reagent, it is thought that the sulfuric acid first sulfonates the acetic anhydride to give sulfoacetic anhydride (6.122) as the acylating species. This results in a faster reaction as the sulfoacetate anion (6.126) is a... 

Activated Esters. Mixed anhydrides may be prepared by reaction of carboxylic acids with trifluoroacetic anhydride. The method has been used widely as a means of activating carboxyl groups to nucleophilic attack. The method has also been highly useful in Friedel-Crafts acylation of arenes (eqs 1 and 2). Sulfonic acids are also activated to nucleophilic attack substituted sulfones result. Intramolecular Friedel-Crafts reactions are also facilitated, but only for formation of six-membered rings. ... 

Sulfonylation. Under Friedel-Crafts reaction conditions, sulfonyl haUdes and sulfonic acid anhydrides sulfonylate aromatics (139), a reaction that can be considered the analogue of the related acylation with acyl haUdes and anhydrides. The products are sulfones. Sulfonyl chlorides are the most frequently used reagents, although the bromides and fluorides also react ... 

A heterocyclic ring may be used in place of one of the benzene rings without loss of biologic activity. The first step in the synthesis of such an agent starts by Friedel-Crafts-like acylation rather than displacement. Thus, reaction of sulfenyl chloride, 222, with 2-aminothiazole (223) in the presence of acetic anhydride affords the sulfide, 224. The amine is then protected as the amide (225). Oxidation with hydrogen peroxide leads to the corresponding sulfone (226) hydrolysis followed by reduction of the nitro group then affords thiazosulfone (227). ... 

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