Friedel—Crafts reactions

Enantioselective Friedel-Crafts reactions using metal-based chiral catalysts or chiral organocatalysts have been investigated extensively because the reactions directly provide alkylated arenes, a pharmacologically important substructure, in optically active forms. The chiral phosphoric acid catalyzed Friedel-Crafts reaction was first accomplished via the activation of imines but, currently, the scope of the electrophilic components has been broadened to include the Michael addition to nitroalkenes, a, 3-unsaturated carbonyl compounds, and so on. 

As mentioned above, a range of enantioselective transformations have been established using chiral phosphoric acids via the activation of imines and related nitrogen-substituted substrates. In contrast, the activation of carbonyl compounds, including a,P-unsaturated carbonyl compounds, by chiral phosphoric acids has been limited. In 2008, Zhou, He, and coworkers achieved the asymmetric Friedel-Crafts alkylation reaction of indole derivatives with 1,3-diaryl a,p-unsaturated 

Shi and coworkers have identified BF3 OEt2 as the best Lewis acid for the formation of the ring-opened product (149) (Equation 89) [91]. Other Lewis acids and Bronsted acids failed to yield any appreciable amount of the desired product in this novel Friedel-Crafts reaction. 

More recently, Balme and coworkers reported a new route to methylenetetrahy-drofluorene products (151) in very high yields via BF3 OEt2 induced intramolecular Friedel-Crafts cyclization of 1,3-bis-exocylic dienes (150) (Equation 90) [92]. 

The treatment of aromatic compounds with benzyl halides in the presence of a 

Introduction of an acyl group onto an aromatic substrate by treating the substrate with an acyl halide or anhydride in the presence of a Lewis acid. 

Friedel, C. Crafts, J. M. Compt. Rend. 1877, 84, 1392. Charles Friedel (1832-1899) was born in Strasbourg, France. He earned his Ph.D. in 1869 under Wurtz at Sorbonne and became a professor and later chair (1884) of organic chemistry at Sorbonne. Friedel was one of the founders of the French Chemical Society and served as its president for four terms. James Mason Crafts (1839-1917) was bom in Boston, Massachusetts. He studied under Bunsen and Wurtz in his youth and became a professor at Cornell and MIT. From 1874 to 1891, Crafts collaborated with Friedel at Ecole de Mines in Paris, where they discovered the Friedel-Crafts reaction. He returned to MIT 

Metivier, P. Friedel-Crafts Acylation In Friedel-Crafts Reaction Sheldon, R. A. Bek-kum, H. eds., WUey-VCH New York. 2001, ppl61-172. (Review). 

Acetylating agent vinyl acetate, 14- 99%ee isopropenyl acetate 

The MBH adducts, derived from methyl acrylate and aldehydes, have been employed successfully to the general synthesis of 3-arylidene(alkylidene)chro-man-4-ones 94, which involved an intramolecular Friedel-Crafts reaction as 

Attempts to obtain indene derivatives via the intramolecular Friedel-Crafts reaction of MBH adducts obtained from aromatic aldehydes and methyl 

Subsequently, Basavaiah and Kim independantly developed a simple one-pot stereoselective transformation of alkyl 3-aryl-3-hydroxy-2-methylene-propanoates 104, the MBH adducts obtained from acrylate and aromatic 

---

The most widely used reactions are those of electrophilic substitution, and under controlled conditions a maximum of three substituting groups, e.g. -NO2 (in the 1,3,5 positions) can be introduced by a nitric acid/sul-phuric acid mixture. Hot cone, sulphuric acid gives sulphonalion whilst halogens and a Lewis acid catalyst allow, e.g., chlorination or brom-ination. Other methods are required for introducing fluorine and iodine atoms. Benzene undergoes the Friedel-Crafts reaction. ... 

Prepared by the dehydration of benzamide. Hydrolysed by dilute acids and alkalis to benzoic acid. Good solvent. benzopheDone,C]3HioO,PhC(0)Ph. Colourless rhombic prisms, m.p. 49 C, b.p. 306°C. Characteristic smell. It is prepared by the action of benzoyl chloride upon benzene in the presence of aluminium chloride (Friedel-Crafts reaction) or by the oxidation of di-phenylmethane. It is much used in perfumery. Forms a kelyl with sodium. 

Methods of producing B —C bonds include hydroboration, nucleophilic displacement at a boron atom in BX., (X = halogens or B(0R>3) by e.g. a Grignard reagent, and a psewiio-Friedel-Crafts reaction with an aromatic hydrocarbon, BX3, and AICI3. 

Aluminium chloride is used extensively in organic chemistry as a catalyst, for example in the Friedel-Crafts reaction ... 

There are finer details to be extracted from such Kohonen maps that directly reflect chemical information, and have chemical significance. A more extensive discussion of the chemical implications of the mapping of the entire dataset can be found in the original publication [28]. Gearly, such a map can now be used for the assignment of a reaction to a certain reaction type. Calculating the physicochemical descriptors of a reaction allows it to be input into this trained Kohonen network. If this reaction is mapped, say, in the area of Friedel-Crafts reactions, it can safely be classified as a feasible Friedel-Qafts reaction. 

TTie true ketones, in which the >CO group is in the side chain, the most common examples being acetophenone or methyl phenyl ketone, C HjCOCH, and benzophenone or diphenyl ketone, C HjCOC(Hj. These ketones are usually prepared by a modification of the Friedel-Crafts reaction, an aromatic hydrocarbon being treated with an acyl chloride (either aliphatic or aromatic) in the presence of aluminium chloride. Thus benzene reacts with acetyl chloride... 

The Friedel-Crafts Reaction, in which an aromatic hydrocarbon reacts with an alkyl halide under the influence of aluminium chloride ... 

The p-methylacetophenone is readily prepared by the Friedel-Crafts reaction cf. p. 254), toluene being treated with acetyl chloride in the presence of alumfnium chloride. The toluene is employed in considerable excess so that it... 

By the Fries reaction. This is a variant of the Friedel-Craft reaction it consists in the conversion of an ester of a phenol to the corresponding o- and p-hydroxyketone, or a mixture of both, by treatment with anhydrous aluminium chloride ... 

The commercial product, m.p. 53-55°, may be used. Alternatively the methyl -naphthyl ketone may be prepared from naphthalene as described in Section IV,136. The Friedel - Crafts reaction in nitrobenzene solution yields about 90 per cent, of the p-ketone and 10 per cent, of the a-ketone in carbon disulphide solution at — 15°, the proportions ore 65 per cent, of the a- and 35 per cent, of the p-isomer. With chlorobenzene ns the reaction medium, a high proportion of the a-ketone is also formed. Separation of the liquid a-isomer from the solid p-isomer in Such mixtures (which remain liquid at the ordinary temp>erature) is readily effected through the picrates the picrate of the liquid a-aceto compound is less soluble and the higher melting. 

Benzilic acid rearrangement Benzoin reaction (condensation) Blanc chloromethylation reaction Bouveault-Blanc reduction Bucherer hydantoin synthesis Bucherer reaction Cannizzaro reaction Claisen aldoi condensation Claisen condensation Claisen-Schmidt reaction. Clemmensen reduction Darzens glycidic ester condensation Diazoamino-aminoazo rearrangement Dieckmann reaction Diels-Alder reaction Doebner reaction Erlenmeyer azlactone synthesis Fischer indole synthesis Fischer-Speior esterification Friedel-Crafts reaction... 

Review Problem 6 Some chemists who were investigating the possibility of reversible Friedel-Crafts reactions, wanted an activated aromatic ring cormected to a branched alkyl chain and chose to make TM 82. How would you do it ... 

Synthesis hote that there is only one activated site for the Friedel-Crafts reaction - o and p to the two methyl groups but not between them for steric reasons ... 

Seeing the aromatic ketones in a and c we might have a Friedel-Crafts reaction in mind. Continue tiiese two a stage further. 

Analysis The one functional group is something of a red herring since we shall put in the acetyl side chain by a Friedel-Crafts reaction on the real target molecule, 399A ... 

Laurino examined a similar method in which methanesulfonanilides were alkylated with bromoacetaldehyde diethyl acetal and then cyclized with TiCU[4J. 1 hese methods presumably involve generation of an electrophilic intermediate from the acetal functionality, followed by an intramolecular Friedel-Crafts reaction. As a consequence, the cyclization is favoured by ER substituents and retarded by EW groups on the benzene ring. 

Acetamido-4-methylthiazole does not react with acetyl chloride in the Friedel-Crafts reaction (172. 407, 449). 

Alkylation of benzene with alkyl halides m the presence of aluminum chloride was discovered by Charles Friedel and James M Crafts m 1877 Crafts who later became president of the Massachusetts Institute of Technology collaborated with Friedel at the Sorbonne m Pans and together they developed what we now call the Friedel-Crafts reaction into one of the most useful synthetic methods m organic chemistry... 

Other limitations to Friedel-Crafts reactions will be encountered in this chap ter and are summarized in Table 12 4 (page 511)... 

Alkenyl halides such as vinyl chloride (H2C=CHC1) do not form carbocations on treatment with aluminum chloride and so cannot be used m Friedel-Crafts reactions Thus the industrial preparation of styrene from benzene and ethylene does not involve vinyl chloride but proceeds by way of ethylbenzene... 

Another version of the Friedel-Crafts reaction uses acyl halides instead of alkyl halides and yields aryl ketones... 

Neither Friedel-Crafts acylation nor alkylation reactions can be earned out on mtroben zene The presence of a strongly deactivating substituent such as a nitro group on an aromatic ring so depresses its reactivity that Friedel-Crafts reactions do not take place Nitrobenzene is so unreactive that it is sometimes used as a solvent m Friedel-Crafts reactions The practical limit for Friedel-Crafts alkylation and acylation reactions is effectively a monohalobenzene An aromatic ring more deactivated than a mono halobenzene cannot be alkylated or acylated under Friedel-Crafts conditions... 

Vinylic halides and aryl halides do not form carbocations under conditions of the Friedel-Crafts reaction and so cannot be used in place of an alkyl halide or an acyl halide... 

Friedel-Crafts reactions are normally not successful when attempted on an aryl amine but can be carried out readily once the ammo group is protected... 

Electrophilic aromatic substitution (Sec tion 22 14) Arylamines are very reac tive toward electrophilic aromatic sub stitution It IS customary to protect arylamines as their N acyl derivatives before carrying out ring nitration chio rination bromination sulfonation or Friedel-Crafts reactions... 

As shown in the sixth entry of Table 24 4 C acylation of phenols is observed under the customary conditions of the Friedel-Crafts reaction (treatment with an acyl chloride or acid anhydride m the presence of aluminum chloride) In the absence of aluminum chloride however O acylation occurs instead... 

---