Friedel-Crafts reaction with alkenes

The Fiiedel-Ciafts alkylation of aiomatics with the lesonance-stabihzed ttichloiocyclopiopenium ttiflate offers a synthetic pathway to ttiaiyl cyclopiopenium salts (26). The ttichloiocyclopiopenium ion has also been shown to undergo Friedel-Crafts reaction with alkenes and alkynes to give trivinyl and tri(halovinyl) cyclopiopenium ions. 

Friedel-Crafts reactions with alkenes are synthetically attractive but, as with alkyl halides, are most useful when stable cations are formed and when done intramolecularly. An internal Friedel-Crafts cyclization with... 

Aminophenols from anilines, 35, 2 Anhydrides of aliphatic dibasic acids, Friedel-Crafts reaction with, 5, 5 Anion-assisted sigmatropic rearrangements, 43, 2 Anthracene homologs, synthesis of, 1, 6 Anti-Markownikoff hydration of alkenes, 13, 1... 

At higher temperatures, C—H and C—C bonds may be similarly broken. Thus, zeolite catalysts may be used for (i) alkylation of aromatic hydrocarbons (cf. the Friedel-Crafts reactions with AICI3 as the Lewis acid catalyst), (ii) cracking of hydrocarbons (i.e., loss of H2), and (Hi) isomerization of alkenes, alkanes, and alkyl aromatics. 

The course of the Friedel-Crafts reaction of alkenes is commonly considered to proceed by reaction of the alkene with the reactive acylating agent to form the 3-ketocarbenium ion, which can then either react with a nucleophile (usually halide) to give overall addition to the double bond, or eliminate a proton, forming unsaturated products (Scheme 1). 

The first stage is an aliphatic Friedel-Crafts reaction with an acylium ion attacking the alkene. 

Subsequently, MBH adducts were successfully utilized as novel stereodefined electrophiles in the Friedel-Crafts reaction with benzene in the presence of a Lewis acid " and sulfuric acid, leading to the stereoselective synthesis of (Z)- and ( )-functionalized trisubstituted alkenes. Notably, MBH adducts obtained from acrylonitrile provide high (Z)-stereoselectivities, while adducts derived from methyl acrylate and aromatic aldehydes give high ( )-stereo-selectivities. When the MBH adducts drived from methyl acrylate and aliphatic aldehydes were involved in the Friedel-Crafts reaction, no significant stereoselectivity was observed (Scheme 3.29). 

Homologation of Arenes and Alk-l-enes, Methoxy(phenyl-thio)trimethylsilylmethane undergoes Friedel-Crafts reaction with arenes in the presence of Lewis acids such as titanium(IV) chloride and tin(IV) chloride to afford (aryl(phenylthio)methyl)-trimethylsilanes (eq 12). This reagent also reacts with terminal alkenes in the presence of SnCU to give ene products (eq 13). ... 

Friedel-Crafts alkylation using alkenes has important industrial appHcations. The ethylation of benzene with ethylene to ethylbenzene used in the manufacture of styrene, is one of the largest scale industrial processes. The reaction is done under the catalysis of AlCl in the presence of a proton source, ie, H2O, HCl, etc, although other catalysts have also gained significance. 

As catalysts Lewis acids such as AICI3, TiCU, SbFs, BF3, ZnCh or FeCl3 are used. Protic acids such as FI2SO4 or FIF are also used, especially for reaction with alkenes or alcohols. Recent developments include the use of acidic polymer resins, e.g. Nafion-Fl, as catalysts for Friedel-Crafts alkylations and the use of asymmetric catalysts. ... 

Alkenes can be acylated with an acyl halide and a Lewis acid catalyst in what is essentially a Friedel-Crafts reaction at an aliphatic carbon. ° The product can arise by two paths. The initial attack is by the acyl cation RCO (or by the acyl halide free or complexed see 11-14) at the double bond to give a carbocation ... 

Apart from the alkyl halide-Lewis acid combination, two other sources of carbo-cations are often used in Friedel-Crafts reactions. Alcohols can serve as carbocation precursors in strong acids such as sulfuric or phosphoric acid. Alkylation can also be effected by alcohols in combination with BF3 or A1C13.37 Alkenes can serve as alkylating agents when a protic acid, especially H2S04, H3P04, and HF, or a Lewis acid, such as BF3 and A1C13, is used as a catalyst.38... 

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... 

Note This reaction involves a polar acidic mechanism, not a free-radical mechanism It is a Friedel-Crafts alkylation, with the slight variation that the requisite carbocation is made by protonation of an alkene instead of ionization of an alkyl halide. Protonation of C4 gives a C3 carbocation. Addition to Cl and fragmentation gives the product. 

Aromatic compounds are usually readily alkylated or acylated by a Friedel-Crafts reaction.150 The combination of reagents used most commonly for aromatic alkylation is an alkyl halide with a strong Lewis acid (Equation 7.65). However, alkenes, alcohols, mercaptans, and a number of other types of organic... 

Friedel-Crafts acylation of alkenes.9 C2H5A1C12 is an effective catalyst for acylation of alkenes with acyl chlorides or anhydrides in CH2C12. The reaction proceeds in higher yield than that previously reported with other Lewis acid catalysts (such as ZnCl2). The reaction provides a useful route to /J,y-enones. 

Acidic chloroaluminate ionic liquids were used as reaction media for Friedel-Crafts reactions as early as 1976 [34], Systematic investigations into Friedel-Crafts alkylations of benzene with the same acidic systems followed in 1986 by Wilkes et al. [35]. The alkylation of benzene with alkenes in acidic imidazolium chloroaluminate melts was disclosed in a patent by BP Chemicals in 1994 [36]. Here, as advantages over the reaction with aluminum trichloride in organic solvents, claims are made regarding the easy isolation of the product, the practically total reusability of the liquid catalyst and the better selectivity to the desired products. 

Friedel-Crafts reactions can also be done with alcohols in the presence of mineral acid. The acid leads to the elimination of water from the alcohol resulting in the formation of an alkene that can then be converted to a carbocation ... 

Friedel-Crafts acylation of alkenes (Daizens-Nenitzescu reaction ) with unsaturated acylium ions generated from acid halides and Lewis acids constitutes a general synthesis of divinyl ketones. 

Aromatic hydrocarbons, such as benzene add to alkenes using a ruthenium catalyst a catalytic mixture of AuCVAgSbFs, or a rhodium catalyst, and ruthenium complexes catalyze the addition of heteroaromatic compounds, such as pyridine, to alkynes. Such alkylation reactions are clearly reminiscent of the Friedel-Crafts reaction (11-11). Palladium catalysts can also be used to for the addition of aromatic compounds to alkynes, and rhodium catalysts for addition to alkenes (with microwave irradiation). " Note that vinyhdene cyclopropanes react with furans and a palladium catalyst to give aUylically substituted furans. ... 

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