Friedel-Crafts alkylation, with

Synthesis This route has been carried out successfully (Rec. Trav. Chem., 1958, 77, 854). Note that no AICI3 is needed for Friedel-Crafts alkylation with easily formed t-alkyl compounds. 

Jung, II Nam, and Yoo, Bok Ryul, Friedel-Crafts Alkylations with Silicon... 

Friedel-Crafts Alkylations with Silicon Compounds... 

CHARACTERISTICS OF FRIEDEL-CRAFTS ALKYLATIONS WITH SILICON COMPOUNDS... 

It is well known in the literature that aluminum chloride, a strong Lewis acid, is a very effective catalyst in Friedel-Crafts alkylations with silicon... 

Ferrocene behaves in many respects like an aromatic electron-rich organic compound which is activated toward electrophilic reactions.In Friedel-Crafts type acylation of aromatic compounds with acyl halides, ferrocene is lO times more reactive than benzene and gives yields over 80%. However, ferrocene is different from benzene in respect to reactivity and yields in the Friedel-Crafts alkylation with alkyl halides or olefins. The yields of ferrocene alkylation are often very low. and the separations of the polysubstituted byproducts are tedious. 

TM (15) has been made by nitration followed by Friedel-Crafts alkylation with IIF as catalyst. No doubt the alternative route would be Successful too. 

Friedel-Crafts alkylations are among the most important reactions in organic synthesis. Solid acid catalysts have advantages in ease of product recovery, reduced waste streams, and reduction in corrosion and toxicity. In the past, people have used (pillared) clays (18), heteropolyacids (19) and zeohtes (20) for Friedel-Craft alkylations, with mixed success. Problems included poor catalyst stabihty and low activity. Benzylation of benzene using benzyl chloride is interesting for the preparation of substitutes of polychlorobenzene in the apphcation of dielectrics. The performance of Si-TUD-1 with different heteroatoms (Fe, Ga, Sn and Ti) was evaluated, and different levels of Fe inside Si-TUD-1 (denoted Fei, Fe2, Fes and Feio) were evaluated (21). The synthesis procedure of these materials was described in detail elsewhere (22). 

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. 

Regardless of whether the Pd-catalyzed coupling or alkyne metathesis is utilized to make PAEs, the critical step is the synthesis of the diiodoarene monomers. In this section some of the more interesting syntheses are showcased. The synthesis of dipropynyldi-tert-butylnaphthalene is shown in Scheme 5. Starting from naphthalene, Friedel-Crafts alkylation with 2-chloro-2-methylbutane gives a mixture of two di-tert-butylnaphthalenes that are separated by crystallization. Iodination of the correct isomer is followed by a Pd-catalyzed coupling of propyne to the diiodide to give the desired l,5-dipropynyl-3,8-di-tert-butyl-naphthalene [56] ready for ADIMET. 

Allylchlorosilanes undergo Friedel-Crafts alkylation with aromatic compounds such as benzene derivatives and ferrocene to give [p-(chlorosilyl)alkyl]arene compounds in the presence of Lewis acid catalyst. Allylsilanes containing two or more chlorine atoms on silicon react smoothly with benzene under mild conditions to give alkylation products in good yields [Eq. (15)]. In alkylations of benzene, the reactivity of the allylsilanes increases as the number of chlorine atoms on the silicon increases, but decreases as the number of methyl groups increases. Because the reactivity of allylsilanes is sensitive to the electronic nature of the substituents on the silicon atom, allylsilane selection is an important factor for alkylation reactions. 

Vinylchlorosilanes undergo Friedel Crafts alkylation with aromatic compounds... 

On the basis of these initial results, various rare earth metal triflates, including Sc(OTf)3, Hf(OTf)4 and Yb(OTf)3 were applied as catalysts [27-29]. Recently Beller and coworkers developed efficient Friedel-Crafts alkylations with catalytic amounts of Rh, W, Pd, Pt and Ir complexes [30] or FeCl3 [31-34] as Lewis acid catalysts. However, in the latter cases high catalyst loadings had to be applied. To overcome these major drawbacks, we decided to develop a Bi(III)-catalyzed Friedel-Crafts alkylation of arenes with benzyl alcohols. Although bismuth-catalyzed Friedel-Crafts acylations were well known at this time, Friedel-Crafts alkylations using benzyl alcohols had not been reported. 

Dibenzofuran undergoes Friedel-Crafts alkylation with alkyl ha-lides " " or alkenes in the presence of Lewis acids. The products... 

The mechanism of Friedel-Crafts alkylation with alkyl halides involves initial formation of the active alkylating agent, which then reacts with the aromatic ring. Depending on the catalyst, the solvent, the reaction conditions, and the alkyl halide, the formation of a polarized donor-acceptor complex or real carbocations (as either an ion pair or a free entity) may take place ... 

Rearrangements of this type involving carbocation intermediates often occur in Friedel-Crafts alkylations with primary and secondary alkyl groups larger than C2 and C3. Related carbocation rearrangements are discussed in Sections 8-9B and 15-5E. 

Fujiwara et al.227 tested a nanocomposite material having Nafion immobilized in MCM-41 mesoporous silica in Friedel-Crafts alkylations with benzyl alcohol. Whereas Nafion-MCM-41 showed lower activity in the alkylation of toluene than 13% Nafion SAC-13 under identical conditions, it exhibited increased activity when used in the alkylation of para-xylene. 

Lewis acids such as boron trihalides will also form stronger bonds with fluoride than with the other halogens, and can be used to abstract fluoride selectively from halogenated compounds. Some examples of Friedel-Crafts alkylations with fluoro-haloalkanes in which only fluoride is displaced are sketched in Scheme 4.14. As shown by the last example, however, hydride migrations can readily occur under such strongly acidic reaction conditions. 

Attempting Friedel-Crafts alkylation with primary halides often gives the wrong product by rearrangement of the intermediate cation. If we want to make /-butylbenzene 16, it seems obvious that we should alkylate benzene with an i-butyl halide, e.g. 18 and AICI3. 

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