Friedel-Crafts acylation, advantages over

Friedel-Crafts acylation. The triflate has many advantages over other Lewis acid catalysts for acylation (11 examples, 75-96%). 

A glycosylation technique using the condensation of acylated furanoses and pyranoses with purines under the influence of a Friedel Crafts catalyst has found widespread application. The method offers advantages over the fusion procedure as fewer a-D-anomers and 7-glycosy-lated regioisomers are formed. 

Aryltrifluoromethyl ketones are prepared by reaction of an aryl-lithium with a,a,a-trifluoro-N,N-dimethylacetamide. 2-Acyloxypyridines and N-acylimidazoles, " in conjunction with trifluoroacetic acid, acylate arenes in good yield without the need for a classical Friedel-Crafts catalyst or a preformed mixed anhydride. However, imidazole in trifluoroacetic anhydride is reported to form 2-aryl-Af,JV -diacyl-4-imidazolines with arenes reactive towards electrophilic attack. These adducts are readily hydrolysed by sodium hydroxide to the corresponding aldehyde [equation (14)]. This sequence may offer advantages over the Vilsmeier method of formylation, in that the aldehyde is introduced in a protected form. 

Ethers and esters have not been widely applied in syntheses by the Friedel-Crafts reaction, chiefly because they offer no particular advantage over the alcohols. In fact, with esters of organic acids and aluminum chloride as catalyst, a disadvantage is the simultaneous acylation, which may occur. However, the synthesis of toluene in 60% yield from benzene, methyl sulfate, and aluminum chloride represents the most successful procedure for the monomethylation of benzene (see p. 22). 

From the same element group Ga(OTf)3 demonstrated its advantages in several synthetic applications over similar catalysts [1]. Very low catalyst loadings were enough to drive various acid-catalyzed reactions including Friedel-Crafts alkylation, hydroxyalkylation, and acylation... 

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