Aromatic Friedel-Crafts alkylation

TeClf catalysed Friedel-Crafts aromatic alkylation (typical procedure. To a solution of 1-phenylethanol (3.7 g, 30 mmol) in toluene (30 mL) is added slowly TeCl4 (9.7 g, 36 mmol), keeping the temperature at 25°C (exothermic reaction). Small amounts of white precipitate appear immediately, and after a few minutes the colour of the mixture becomes dark brown. The mixture is stirred for 3 h and then quenched with HgO (20 mL). The organic layer is separated, washed with brine (2x20 mL) and dried (MgS04). Evaporation of the solvent leaves an oily residue which is distilled under vacuum, giving a mixture of 1-phenyl-1-tolylethanes (4.9 g (83.3%) b.p. 117-128°C/1 torr). GLC analysis (silicone OV-101, 0.24 mm X 30 m capillary column at 100-260°C, 4°C min i) reveals an ortholpara ratio of 12 88. 

Many of the reactions of BF3 are of the Friedel-Crafts type though they are perhaps not strictly catalytic since BF3 is required in essentially equimolar quantities with the reactant. The mechanism is not always fully understood but it is generally agreed that in most cases ionic intermediates are produced by or promoted by the formation of a BX3 complex electrophilic attack of the substrate by the cation so produced completes the process. For example, in the Friedel-Crafts-type alkylation of aromatic hydrocarbons ... 

Reactions other than those of the nucleophilic reactivity of alkyl sulfates involve reactions with hydrocarbons, thermal degradation, sulfonation, halogenation of the alkyl groups, and reduction of the sulfate groups. Aromatic hydrocarbons, eg, benzene and naphthalene, react with alkyl sulfates when catalyzed by aluminum chloride to give Friedel-Crafts-type alkylation product mixtures (59). Isobutane is readily alkylated by a dipropyl sulfate mixture from the reaction of propylene in propane with sulfuric acid (60). 

Like other aromatic compounds, aromatic ethers can undergo substitution in the aromatic ring with electrophilic reagents, eg, nitration, halogenation, and sulfonation. They also undergo Friedel-Crafts (qv) alkylation and acylation. 

The Friedel-Crafts alkylation and acylation are of very little, if any, synthetic interest when applied to heterocyclic aromatic bases the substitution of protonated heterocycles by nucleophilic carbon-centered radicals is instead successful. This reaction, because of the dominant polar effect which is mainly related to the charge-transfer character of the transition state (Scheme 1), reproduces most of the aspects of the Friedel-Crafts aromatic substitution, but reactivity and selectivity are the opposite. 

Section 5.2 aromatic Friedel-Crafts-type alkylations C. Perego and P. Ingallina, Catal. Today 2002, 73, 3 A. Corma, Chem. Rev. 1995, 95, 559 alkane cracking and isomerization Y. Ono, Catal. Today 2003,81, 3 A. Feller and J. A. Lercher, Adv. Catal. 2004, 48, 229 isoparaffin-olefin alkylation A. Corma and A. Martinez, Catal. Rev. Sci. Eng. 1993, 35, 483 acid-base catalysis with metal oxides K. Tanabe and W. F. Floelderich, Appl. Catal. A Gen. 1999, 181, 399. 

Friedel Crafts type alkylations of benzene by alkenes involve the initial formation of a lattice associated carbenium ion, formed by protonation of the sorbed olefin. The chemisorbed alkene is covalently bound to the zeolite in the form of an alkoxy group and the carbenium ion formed exists only in the transition state. As would be expected fixjm conventional Friedel Crafts alkylation, the reaction rate over acidic molecular sieves also increases with the degree of substitution of the aromatic ring (tetramethyl > trimethyl > dimethyl > methyl > unsubstituted benzene). The spatial restrictions induced by the pore size and geometry frequently inhibit the formation of large multisubstituted products (see also the section on shape selectivity). 

N-Acyliminium ion pools react with various carbon nucleophiles as summarized in Scheme 5.16. For example, allylsilanes, silyl enol ethers, Grignard reagents, and 1,3-dicarbonyl compounds serve as good nucleophiles. Aromatic and heteroaromatic compounds also react as nucleophiles with N-acyliminium ion pools to give Friedel-Crafts-type alkylation products.N-Acyliminium ions are known to serve as electron-deficient 4n components and undergo [4 -F 2] cycloaddition with alkenes and alkynes. Usually these reactions take place very quickly, and therefore N-acyliminium ion pools serve as effective reagents for flash chemistry. 

The carbon-carbon bond may be formed when a carbon nucleophile is used in the combination system. The most representative examples include the Friedel-Crafts-type alkylation of aromatics (Scheme XI, equation 1) (18) and the acid-catalyzed Diels-Alder reaction (Scheme XI, equation 2). The reaction of a combination system consisting of aluminum chloride and 1,3-dienes leading to regio- and stereoselective functionalization of 1,3-dienes via the thienium cation Diels-Alder reaction (19) (Scheme XI, equation 3) is described here. 

Certain compounds (electrophilic) can react with phenols (nucleophilic). The nucleophilic activity can be either in the iaromatic ring or the oxygen in the hydroxyl group. Examples of electrophilic aromatic substitution include nitration, halogenation, Friedel-Crafts reactions (alkylation and acylation), and sulfonation. The halogenation example shown below is a polysubstitution reaction involving bromine. The polysubstitution usually occurs when polar solvents are used. 

In a similar reaction, called the Friedel-Crafts reaction, alkyl groups can be substituted onto an aromatic ring by reacting an alkyl halide with an aromatic compound in the presence of AICI3 as a catalyst ... 

Friedel-Crafts alkylation is one of the most frequently used and widely studied reactions in organic chemistry. Since the initial discovery by Charles Friedel and James Mason Crafts in 1877, a large number of applications have emerged for the construction of substituted aromatic compounds. Friedel-Crafts alkylation processes involve the replacement of C—H bond of an aromatic ring by an electrophilic partner in the presence of a Lewis acid or Bronsted acid catalyst. Particularly, catalytic asymmetric Friedel-Crafts alkylation is a very attractive, direct, and atom-economic approach for the synthesis of optically active aromatic compounds. However, it took more than 100 years from the discovery of this reaction until the first catalytic asymmetric Friedel-Crafts (AFC) alkylation of naphthol and ethyl pyruvate was realized by Erker in 1990. Nowadays, owing to continued efforts in developing... 

Physical organic studies have demonstrated that lerl-butylsulfonyl chloride decomposes cleanly to the tert-butyl cation in water over a pH range 3.5 to 13.0. Clean teri-butyl cation formation is also the only significant reaction in methanol-chloroform. The subsequent product spectrum is a function of the reaction conditions. tert-Butylsulfonyl chloride, is used for the tert-butylation of aromatic compounds in a Friedel-Crafts desulfonylative alkylation in the presence of aluminum chloride-nitromethane as catalyst at 25 °C (eq 1). Alkylation products were obtained free of contamination by the sulfonylation product. 

Ferrocene undergoes a large number of typical ionic aromatic substitution reactions that include Friedel-Crafts acylation, alkylation, metalation, sulfonation, and aminomethylation. Figure 6-1 outlines some of the more... 

Intermediates are produced by a variety of reactions. Aromatic hydrocarbons undergo four electrophilic substitution reactions— the Friedel-Crafts reaction (alkylation and acylation), halogenation, nitration, and sul-fonation—as well as oxidation and reduction. These reactions lead to substituted hydrocarbons that can be further reacted to provide intermediates for dyes. The number of dye intermediates actually or potentially available is very large, and the technology of their manufacture is an important part of industrial organic chemistry. Intermediates are used not only for dye manufacture but also for the manufacture of other important products such as pharmaceuticals. 

Guanidine was shown to be an efficient organocatalyst for the Friedel-Crafts-type alkylation of indoles with aromatic fluoromethyl ketones, yielding up to 98% of trifluoromethyl-indolyl-phenylethanols, potential intermediates for pharmaceutical and agrochemical synthesis [114]. 

We will show here the classification procedure with a specific dataset [28]. A reaction center, the addition of a C-H bond to a C=C double bond, was chosen that comprised a variety of different reaction types such as Michael additions, Friedel-Crafts alkylation of aromatic compounds by alkenes, or photochemical reactions. We wanted to see whether these different reaction types can be discerned by this... 

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