Alkyl arenes

In eontrast, dialkylhalonium salts sueh as dimethylbromonium and dimethyliodonium fluoroantimonate, whieh we prepared from excess alkyl halides with antimony pentafluoride or fluoroantimonie acid and isolated as stable salts (the less-stable chloronium salts were obtained only in solution), are very effective alkylating agents for heteroatom eompounds (Nu = R2O, R2S, R3N, R3P, ete.) and for C-alkylation (arenes, alkenes). 

It has become clear that benzoate occupies a central position in the anaerobic degradation of both phenols and alkylated arenes such as toluene and xylenes, and that carboxylation, hydroxylation, and reductive dehydroxylation are important reactions for phenols that are discussed in Part 4 of this chapter. The simplest examples include alkylated benzenes, products from the carboxylation of napthalene and phenanthrene (Zhang and Young 1997), the decarboxylation of o-, m-, and p-phthalate under denitrifying conditions (Nozawa and Maruyama 1988), and the metabolism of phenols and anilines by carboxylation. Further illustrative examples include the following ... 

T1 resin traceless linker [131-134], synthesis of phenols [135], biaryls, alkyl arenes [136, 137], azides [138], aromatic hydrazines, halides [cf. 128, 129, 139], ester, azo compounds, cinno-lines [140], benzotriazoles [141]... 

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. 

Benzylische, allylische und tertiare Nitro-aliphaten lassen sich unter Friedel-Crafts-Be-dingungen mit Zinn(IV)-chlorid als Katalysator in Benzol, Toluol, Methoxy- oder 1,2-Dimethyl-benzol in guten Ausbeuten unter nukleophiler Substitution der Nitro-Gruppe in Alkyl-arene umwandeln4,8 3-5 ... 

Alkyl Arenes ArCHj------- ArCHO, ArCH R-------- ArCOR... 

Friedel-Crafts type reactions of strongly deactivated arenes have been the subject of several recent studies indicating involvement of superelectrophilic intermediates. Numerous electrophilic aromatic substitution reactions only work with activated or electron-rich arenes, such as phenols, alkylated arenes, or aryl ethers.5 Since these reactions involve weak electrophiles, aromatic compounds such as benzene, chlorobenzene, or nitrobenzene, either do not react, or give only low yields of products. For example, electrophilic alkylthioalkylation generally works well only with phenolic substrates.6 This can be understood by considering the resonance stabilization of the involved thioalkylcarbenium ion and the delocalization of the electrophilic center (eq 4). With the use of excess Fewis acid, however, the electrophilic reactivity of the alkylthiocarbenium ion can be... 

The metal-bound carbon atom in organopalladium(II) complexes can formally react either as an electrophile or as a nucleophile. Treatment of arylpalladium(II) complexes with alkyl halides, for example, yields products of homo- or cross-coupling, possibly via intermediate formation of hexacoordinated Pd(IV) complexes [31,33] (Scheme8.1). Treatment of the same type of complex with alkyl Grignard reagents or other carbon nucleophiles, on the other hand, also yields the corresponding alkyl arenes via nucleophilic displacement of a ligand followed by reductive elimination (Scheme 8.1). 

Friedel-Crafts alkylation. Reaction of arenes with acid chlorides in CH2C12 with AICI3 (1 equiv.) and (C2H5)3SiH (2.5-3 equiv.) results in the alkylated arene by deoxygenation of the intermediate acylated arene. Yields of 95% are obtainable, and this procedure avoids the problem of polyalkylation observed in regular Friedel-Crafts reactions.3... 

These catalytic reactions provide a unique pathway for addition of aromatic C-H bonds across C=C bonds. In contrast with Friedel-Crafts catalysts for olefin hydroarylation, the Ru-catalyzed hydrophenylation reactions of a-olefins selectively produce linear alkyl arenes rather than branched products. Although the selectivity is mild, the formation of anti-Markovnikov products is a unique feature of the Ru(II) and Ir(III) catalysts discussed herein. Typically, the preferred route for incorporation of long-chain linear alkyl groups into aromatic substrates is Friedel-Crafts acylation then Clemmensen reduction, and the catalysts described herein provide a more direct route to linear alkyl arenes. 

Ir(III) complexes can also be used to catalyze the hydroarylation of olefins [5, 6], The catalyst precursors (acac-0,0)2Ir(Ph)(L) (L= pyridine or H20) and [Ir(w-acac-0,0,C3)(acac-0,0)(acac-C3)]2 have been reported and are depicted in Scheme 3, with representative catalytic reactions. Among these catalyst precursors, (acac-0,0)2Ir(Ph)(H20) has been demonstrated to be the most active system [5], The lin-ear-to-branched ratios observed for Ir(III) catalyzed reactions of a-olefins are remarkably similar to those obtained using TpRu(CO)(NCMe)(Ph). For example, hydrophenylation of propene using 11 r (a-acac- O, O,C ) (acac-O, O) (acac-C3) ]2 as catalyst produces a 1.6 1 ratio of linear propylbenzene to cumene (identical to the ratio observed using the Ru(II) catalyst). Similar to the TpRu(CO)(NCMe)(R) catalysts, the regioselectivity of hydroarylation of ethylene that incorporates monoalkyl arenes produces meta- and para-disubstituted alkyl arenes in approximately 2 1 ratio without observation of ortho-disubstituted products. 

Te-alkyl arene- 7>-carboxylate alkyl aroyl tellurium... 

Alkyl Arenes ArCH3 —- ArCHO, ArCH2R —- ArCOR... 

Alkylation of arenes and perfluoro or perchlorofluoro compounds proceeds readily under SbFg catalysis [4,21]. In addition to alkyl halides, alkyl esters and haloesters have also been used to alkylate arenes under these reaction conditions. For example, perfluorotoluene reacts with pentafluorobenzene to form perfluorodiphenylmethane in 68 % yield when the reaction mixture is quenched with HR If H2O is used for quenching, perfluorobenzophenone is obtained in 93 % yield (Eq. 8) [21a]. 

Removal of an electron generally brings about significant thermochemical C-H bond weakening both in a + n) radical cations (i.e. deprotonation in the benzylic position [152]) and a- -n) radical cations (i.e. deprotonation at the a-carbon of amines [153, 154], ethers [155], and thioethers [156]). The kinetic acidity of benzyl radical cations is rather well understood [152d, 157, 158], although occasionally an addition-elimination route was favored over direct proton transfer [159]. For alkyl arene radical cations [160] a linear relationship has been established between logkdep and thermochemical acidity [157]. 

Alkyl Arenes A1CH3 — ArCHO, A1CH2R — ArCOR... 

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