Friedel-Crafts reaction Catalyzed

In addition, this acylating reaction turns out to be very "environmentally friendly" process compared to the classical Friedel-Crafts reaction catalyzed by aluminium chloride, generating only byproducts such as acidic acid which can easily be recovered and recycled. 

Scheme 44 Friedel-Crafts reaction catalyzed by neutral and cationic Pd(ll) complexes...

Friedel-Crafts reactions Catalyzed chemical reactions that involve the alkylation and acylation reaction of aromatics. An e imple is the production of toluene from benzene using chlorome thane in the presence of aluminium chloride catalyst... 

The first report of the enantioselective Friedel-Crafts reaction catalyzed by phosphoric acid 1 was presented by Terada and coworkers (Scheme 11.19) [34]. They reported the 1,2-aza-Friedel-Crafts reaction of 2-methoxyfuran (72) with N-Boc aldimines 5 by means of a catalytic amount of chiral phosphoric acid. In this reaction, stericaUy hindered 3,5-dimesitylphenyl-substituted catalyst Ij was the most effective and the corresponding Friedel-Crafts adducts 73 were obtained with excellent enantioselectivities (86-97% ee). Notably, the reaction could be performed in the presence of as low as 0.5 mol% of Ij without any loss of selectivity (Ar = Ph, 95% yield, 97% ee). 

More recently, a novel one-pot synthesis of enantioenriched polysubstituted cyclopenta[fc]indoles 127 starting with the a-alkylation of aldehydes 125 was established by Xu et al. [51], In the presence of a primary-amine-derived thiourea T1 and a carboxylic acid Al, the reaction between ot,a-disubstituted aldehydes 125 and 3-indolyhnethanol 124 proceeded smoothly to afford alkylation products, which underwent two further consecutive Friedel-Crafts reactions catalyzed by aphosphoric acid PAl to afford the desired polysubstituted cyclic products 127 with excellent stereoselectivities (Scheme 2.36). 

Sometimes, ion-exchanging groups are introduced on to the resins and these are synthesized by first preparing the styrene-divinyl benzene copolymer [as in Eq. (1.7.1)] in the form of beads, and then the chloromethylation is carried out. Chloromethylation is a Friedel-Crafts reaction catalyzed by anhydrous aluminum, zinc, or stannous chloride the polymer beads must be fully swollen in dry chloromethyl methyl ether before adding the catalyst, ZnCla. Normally, the resin has very small internal surface area and the reaction depend heavily on the degree of swelling. This is a solid-liquid reaction and the formed product can be shown to be... 

Despite this early discovery, little attention has been paid to the ILs for catalysis. The first example of RTILs for catalysis in open literature should be the Friedel-Crafts reactions catalyzed with dialkyl imidazolium chloroaluminate ILs by Wikes et al. in 1986 [2]. The research motivation was just to know what would occur when Friedel-Crafts reactions were carried out in the RTILs. The chloroaluminate... 

A good deal of experimental care is often required to ensure that the product mixture at the end of a Friedel-Crafts reaction is determined by kinetic control. The strong Lewis acid catalysts can catalyze the isomerization of alkylbenzenes, and if isomerization takes place, the product composition is not informative about the position selectivity of electrophilic attack. Isomerization increases the amount of the meta isomer in the case of dialkylbenzenes, because this isomer is thermodynamically the most stable. ... 

This activation of the ortho position is most strikingly illustrated in the reactivity of 2,5-dimethylthiophene, which competitive experiments have shown to undergo the SnCb-catalyzed Friedel-Crafts reaction more rapidly than thiophene and even 2-methylthiophene. The influence of the reagent on the isomer distribution is evident from the fact that 2-methoxythiophene is formylated and bromi-nated (with A -bromosuccinimide) only in the 5-position. Similarly, although 3-bromo-2-methylthiophene has been detected in the bromi-nation of 2-methylthiophene with bromine, only the 5-isomer (besides some side-chain bromination) is obtained in the bromination of alkylthiophenes with A -bromosuccinimide. ° However, the mechanism of the latter type of bromination is not established. No lines attributable to 2-methyl-3-thiocyanothiophene or 2-methyl-3-chIoro-thiophene could be detected in the NMR spectra of the substitution products (5-isomers) obtained upon thiocyanation with thiocyanogen or chlorination with sulfuryl chloride. 2-Methyl- and 2-ethyl-thiophene give, somewhat unexpectedly, upon alkylation with t-butyl chloride in the presence of Feds, only 5-t-butyl monosubstituted and... 

Such eliminations do not occur with chloro compounds. 2,5-Dichlorothiophene undergoes AlCU-catalyzed sulfonylation with ben-zenesulfonyl chloride. Attempts to extend this reaction to thiophene, 2,5-dimethylthiophene, and 2-chloro-5-iodothiophene resulted in the formation of intractable tars even with other catalysts. Sul-fones of this type are often prepared in much better yields by using thiophenesulfonyl chlorides and benzenes in the Friedel-Crafts reaction. ... 

This section deals with Bronsted acid and Lewis acid catalyzed reactions, excluding Friedel-Crafts reactions, but including reactions such as nitrations, halogenations, and Claisen rearrangements. Friedel-Crafts reactions are discussed in the subsequent Sections 5.1.2.2 and 5.1.2.3. 

Friedel-Crafts reactions have been studied in detail by Olah [74, 75]. These reactions result in the formation of carbon-carbon bonds and are catalyzed by strong Bronsted or Lewis acids. 

Raston has reported an acid-catalyzed Friedel-Crafts reaction [89] in which compounds such as 3,4-dimethoxyphenylmethanol were cyclized to cyclotriveratrylene (Scheme 5.1-57). The reactions were carried out in tributylhexylammonium bis(tri-fluoromethanesulfonyl)amide [NBu3(QHi3)][(CF3S02)2N] with phosphoric or p-toluenesulfonic acid catalysts. The product was isolated by dissolving the ionic liq-uid/catalyst in methanol and filtering off the cyclotriveratrylene product as white crystals. Evaporation of the methanol allowed the ionic liquid and catalyst to be regenerated. 

To optimize the alkylation conditions, ferrocene was reacted with allyldimethyl-chlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group lO metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. 

The FeCls-catalyzed Friedel-Crafts reactions of electron-rich arenes with imines or aziridines provide a facile and convenient route for the synthesis of p-aryl... 

Scheme 6 Iron(III)-catalyzed conversion of 2-alkylcinnamaldehydes to 2-alkylindanones via a catalytic intramolecular Friedel-Craft reaction...

Friedel-Crafts reaction remains unexplored, possibly due to the difficulty of the cycloalkyne formation. A mild, versatile, and efficient method for the one-step synthesis of substituted dihydro- and tetrahydroisoquinolines has been developed by the FeCl3-6H20-catalyzed intramolecular allenylation/cyclization reaction of benzylamino-substituted propargylic alcohols, representing the first example of the intramolecular Friedel-Crafts reaction of propargylic alcohols (Scheme 8) [24, 25]. FeCls, InCls, and Yb(OTf)3 also exhibit good catalytic activity for the reaction. 

The aluminum trihalides are particularly important Lewis acids in the chemical industry. They promote or catalyze a large variety of reactions. One of the most important applications is the Friedel-Crafts reaction, in which two molecules combine, forming a new C—C bond. For example, aluminum chloride or some other Lewis acid catalyzes the reaction between an acid chloride and benzene to form acetophenone ... 

Under Lewis-acid-catalyzed conditions, electron-rich arenes can be added to alkenes to generate Friedel-Crafts reaction products. This subject will be discussed in detail in Chapter 7, on aromatic compounds. However, it is interesting to note that direct arylation of styrene with benzene in aqueous CF3CO2H containing H2PtCl6 yielded 30-5% zram-PhCH CHR via the intermediate PhPt(H20)Cl4.157 Hydropheny-lation of olefins can be catalyzed by an Ir(III) complex.158... 

Indium trichloride349-351 is a mild Lewis acid that is effective for various kinds of Lewis-acid-catalyzed reactions such as Diels-Alder reactions (Scheme 85), aldol reactions, and Friedel Crafts reactions. Since indium trichloride is stable in water, several aqueous reactions have been investigated (Scheme 85) indium(III) triflate is also used as a Lewis acid. 

Antimony pentachloride is a reactive Lewis acid that can be used for Friedel-Crafts reactions and some other Lewis-acid-catalyzed reactions. The HF-SbF5 system is known as magic acid, and carbocations are stabilized in this medium.353 By using the HF-SbF5 system, alkylation of acetophenone (a relatively unreactive aromatic compound) has been achieved (Scheme 87). 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

We have recently shown that metal-exchanged zeolites give rise to carbocationic reactions, through the interactions with alkylhalides (metal cation acts as Lewis acid sites, coordinating with the alkylhalide to form a metal-halide species and an alkyl-aluminumsilyl oxonium ion bonded to the zeolite structure, which acts as an adsorbed carbocation (scheme 2). We were able to show that they can catalyze Friedel-Crafts reactions (9) and isobutane/2-butene alkylation (70), with a superior performance than a protic zeolite catalyst. 

Prakash, Chlorination and bromination of fullerenes. Nucleophilic methoxylation of polychlorofullerenes and their aluminum trichloride catalyzed friedel-crafts reaction with aromatics to polyarylfullerenes, Journal of American Chemical Society, vol. 113, pp. 9385-9387,1991. 

The use of catalytic SILP materials has been reviewed recently [10] covering Friedel-Crafts reactions [33-37], hydroformylations (Rh-catalyzed) [38], hydrogenation (Rh-catalyzed) [39,40], Heck reactions (Pd-catalyzed) [41], and hydroaminations (Rh-, Pd-, and Zn-catalyzed) [42]. Since then, the SILP concept has been extended to additional catalytic reactions and alternative support materials. In this paper we will present results from continuous, fixed-bed carbonylation and hydroformylation reactions using rhodium-based SILP catalysts as reaction examples demonstrating the advantages of the SILP technology for bulk chemical production. 

Friedel-Crafts reaction org chem A substitution reaction, catalyzed by aluminum chloride in which an alkyl (R —) or an acyl (RCO —) group replaces a hydrogen atom of an aromatic nucleus to produce hydrocarbon or a ketone. fre del krafs re.ak shan ... 

Asides from the application of imines on conjugate addition reactions, Deng [87, 88] reported the first asymmetric chiral thiourea catalyzed Friedel-Crafts reaction of indoles with iV-tosyl imines (Scheme 35). The reaction was receptive to various aromatic, heteroaromatic, and aliphatic imines in good yield and high enantioselec-tivity (Scheme 36). 

Mechanistically, the Brpnsted acid-catalyzed Friedel-Crafts reaction presumably involves a tantomerism of enamide 127 to the corresponding A -acetyl-protected imine. Snbseqnent addition of indole 29 affords amide 128 (Scheme 52). 

In the same year, Enders and coworkers reported an asymmetric one-pot, two-step synthesis of substituted isoindolines 159 in the presence of chiral A-triflyl phosphoramide (R)-Ae (10 mol%, R = d-NO -C H ) (Scheme 67) [87]. The cascade was triggered by a Brpnsted acid-catalyzed aza-Friedel-Crafts reaction of indoles 29 and A-tosyliminoenoates 160 followed by a DBU-mediated aza-Michael cyclization of intermediates 161 to afford the isoindolines 159 in high yields (71-99%) and short reaction times (10 min to 4 h) along with good enantioselectivities (52-90% ee). Longer reaction times (16 h to 10 days) caused increasing formation of the bisindole byproduct 162 (Scheme 68) along with amplified optical purity of isoindolines 159. 

---