Friedel-Crafts reagents

The electrophilic substitution reactions commonly used with aromatic compotmds could not be applied to monosubstituted oxadiazoles 25a, 55 b). The hydrogen atoms in position 3 and 5 of these derivatives could not be replaced by a halogen atom or a nitro group and are also inactive towards Friedel-Craft reagents. 

The oxazolidinediones 94 are crystalline, stable solids that are a convenient source of dipeptides when heated in THF with amino adds. The compounds are prepared fiom N-protected amino adds and phosgene or triphosgene <99JOC2S32>. The diiral oxazolidinediones 95 act as Friedel-Crafts reagents with aromatic hydrocarbons and aluminium chloride, giving the ketones 96 in moderate yield but with high ee <99S423>. ... 

The initiation of tetrahydrofuran polymerization by direct addition of oxonium salts is of interest because it reveals a good deal about the mechanism, but for practical purposes the salts may be formed in the reaction mixture. The obvious method is, of course, to add a little epichlorohydrin to the mixture of monomer and Friedel Crafts reagent for only antimony pentachloride is sufficiently active to start the reaction with monomer alone, but other reactions which accomplish the same purpose are ... 

Nitrobenzene is resistant to acids. Bases at certain concentrations and temperatures do not affect nitrobenzene. Only when boiled with NaOH in alcoholic solution, is nitrobenzene reduced to form azoxybenzene. Nitrobenzene does not react with Friedel-Crafts reagents and can be used as solvent in Friedel-Crafts... 

From Hydrocarbons.—In the presence of aluminium chloride (Friedel-Craft reagent) benzene may be oxidized to phenol. 

From Hydrocarbons, Friedel-Craft.—The aromatic hydrocarbons yield ring carboxy acids by other reactions than those effecting oxidation of a side chain. Carbon dioxide may be introduced directly into a benzene ring, thus converting a hydrogen into.carboxyl. This may be accomplished in the presence of aluminium chloride, Friedel-Craft reagent. 

From Aliphatic Acids.—By the introduction of an aryl radical into an aliphatic acid we may obtain side-chain carboxy acids in which the side chain is the same as in the aliphatic acid. This reaction is effected by the Friedel-Craft reagent, aluminium chloride, with the aromatic hydrocarbon together with a halogen aliphatic acid. 

Reaction of aryl nitrilium ions (40) or imidoyl chlorides (41) with benzonitrile produced the nitrilium species (42), which underwent Friedel-Crafts reaction yielding the quinazoline system (43 Scheme 17). Generation and cyclization of nitrilium species using Friedel-Crafts reagents has since found widespread favor in heteroaromatic synthesis and such procedures have been reviewed in detail. An illustration of its use for a nonbenzenoid aromatic system is given in equation (31). ... 

Earlier mention has been made of the use of Lewis acid and Friedel-Crafts reagents as initiators of carbenium ion formation. Another versatile device is to employ a metal to assist in generation of the carbenium ion. In its simplest form, addition of silver(I) ion to an alkyl halide is an excellent technique for encouraging reaction by means of the 5n 1 pathway. This process was first applied to the Ritter reaction by Cast and Stevens, but yields obtained were modest. A recent elegant application of this technique is the two-step conversion of dodecahedrane into its acetamide derivative (Scheme 45). ... 

Friedel-Crafts reagents (Lewis acids) represent the most widely used class of cationic polymerization catalysts. 

Scheme 8.18 Alkylation of toluene to xylenes over Friedel-Crafts reagents and zeolitic catalysts.

Polymerization of 3,3-bis(chloromethyl)oxacyclobutane may be effected by Friedel-Crafts reagents (e.g., aluminium chloride and boron trifluoride) at low... 

Also obtained by reaction of EKONOL ), an aromatic polyester as Friedel-Crafts reagent, with chlorobenzene in triflic acid solution at 25° for 18 h (28%) [922]. Similar resnlts can be obtained using hydrofluoric acid/boron trifluoride or aluminium chloride in place of triflic acid [922]. 

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