Arenes, alkyl functionalization

XRD samples 638 f alignment defects, displays 756 alignment materials, displays 732 aliphatic chains 125,395 alkanes, solvents 883 alkanoic acids, esterification alkanols, esterification 106 alkenes, solvents 883 alkenyl, terminal substituents alkyl functionalization, arenes alkyl groups... 

Beside the Friedel-Crafts-type alkylation of arenes, the direct functionalization of 2,4-pentanediones is of great interest in Lewis acid catalysis. Although Pd-catalyzed Tsuji-Trost type allylations of 1,3-diketones are known, direct benzylation procedures catalyzed by Lewis acids are less explored [40-43]. Based on the previously described Friedel-Crafts alkylation of arenes and heteroarenes, the Rueping group developed a Bi(OTf)3-catalyzed benzylation of 2,4-pentanediones. Alcohols such as benzyl, allyl or cinnamyl alcohols were used as the electrophilic component to yield important 2-alkylated 1,3-dicarbonyl compounds. Initially, different Bi(III) salts were screened. In contrast... 

One of the most common examples of an electrophilic aromatic substitution is Friedel-Crafts alkylation [40], These days, many important industrial processes are based on this type of Friedel-Crafts-chemistry [41]. The manufacture of high-octane gasoline, ethylbenzene, synthetic rubber, plastics and detergent alkylates are examples. Moreover, the Friedel-Crafts alkylation is among the most fundamental and convenient processes for C—C bond formation on arenes, especially for the synthesis of fine chemicals and agrochemicals containing functionalized arenes and heteroarenes. 

The final option available to a u-alkylpalladium intermediate from Heck alkylation occurs if another alkene or alkyne function is situated properly to participate in a further Heck-type carbopalladation (equation 161)318,319. In properly constructed systems, more than one further carbopalladation is feasible, and many examples of these cascade car-bopalladations have been reported. Several have been quite spectacular (equation 162)320. Fused, spirocyclic and bridged bicyclic ring systems have been prepared in this manner. The process may also create as many as five rings in one step, with five-,six- and three-membered rings321 being the most suitable for preparation (equation 163). Alternatively, the proper orientation of double and triple bonds allows cyclotrimerization to highly functionalized arenes or fulvenes (equation 164)322,279. 

Regioselective F-C acylations of carboxylic anhydrides can be accompanied by other Lewis acid mediated reactions in tandem. Recently, a general method for the Lewis acid mediated intramolecular cyclization of keto ester alkyl substituted arenes to functionalized 1-indanones was reported by Pillion. Thus treatment of Meldrum s acid analogue 23 under a variety of... 

The above examples demonstrate that Friedel-Crafts type reactions of functional arenes can be profitably performed using ruthenium(II) catalysts without Lewis acid addition. Whereas only ortho transformations of C-H bonds were observed before, the sulfonation reaction and the alkylation with secondary alkyl halides offer a challenging modification of the regioselectivity that is starting to occur at the mefa-position of the functional groups and illustrate the specific positive role of the ruthenium atom in the metallacycle intermediate. 

Simple ruthenium(II) catalysts can now perform heterocycle directed alkylation and Friedel-Crafts type reactions at orf/io-positions of arenes and heteroarenes. The former reaction takes places without p elimination and the latter reaction takes place without addition of Lewis acid to form arenes containing a ketone, amide, or ester functionality. Hydroarylation of strained alkenes can be performed to obtain ortho alkyl (hetero)arenes and alkylation of sp C-H bond can be observed using alcohol as a precursor. 

In the case of hexahomotriazacalix[3]arene (1), (9-alkylation by picolyl chloride was easily achieved with sodium hydride as a base in DMF (78%). However, even without (9-alkylation, functional groups can be introduced into the azactilixarene structures by the one-step procedure described here. Attachment of various side arms to bifunctioneil azacalixarene systems should allow the construction of new macrocyclic host molecules with multi-binding sites. 

Fagnou and co-workers reported on the use of a palladium source in the presence of different phosphine ligands for the intramolecular direct arylation reaction of arenes with bromides [56]. Later, they discovered that new conditions employing palladium complex 27 promoted the direct arylation of a broad range of aryl chlorides to form six- and five-membered ring biaryls including different functionalities as ether, amine, amide and alkyl (Scheme 7.11) [57]. 

In contrast with the role of cofactor B12 in methionine synthase (methyl group transfer to a thiol), functional Bi2 model complexes have provided a formidable challenge. Several oxime alkyl-cobalt (structural) B12 models when reacted with arene- and alkanethiolates lead only to... 

Gold-catalyzed direct C-H functionalizations enable the formation of polyalkylated arenes under mild conditions. In many cases, branched products are obtained. Two mechanisms are thought to operate with electron-rich arenes, an S si2-type mechanism via Au(lll) leads to the linear product. The branched product is obtained via a Friedel-Craft-type alkylation. A silver salt is often added and is believed to generate a more electrophilic Au(m) species. Often regioselectivities are poor and symmetric arenes are employed. Intramolecular variants as well as Michael additions are also known (Equations (72)-(74)).71,71a,71b... 

The iridium complex composed of l/2[ Ir(OMe)(cod)2 ] and 4,4 -di-/ r/-butyl-2,2 -bipyridine (dtbpy) shows a high catalytic activity for aromatic G-H silylation of arenes by l,2-di-/z r/-butyl-l,l,2,2,-tetrafluorodisilane.142 The reaction of 1,2-dimethylbenzene with l,2-di-/< r/-butyl-l,l,2,2,-tetrafluorodisilane in the presence of l/2[ Ir(OMe)(cod)2 ] and dtbpy gives 4-silyl-l,2-dimethylbenzene in 99% yield (Equation (103)), which can be utilized for other functionalizations such as arylation and alkylation. 

Dialkoxymethyllithium compounds, for example 2-lithio-l,3-dioxan (311), are generated in situ as shown in equation 69, either by reductive lithiation of a phenyl thioether with a lithium arene or by transmetallation of the corresponding trialkylstannyl compound. Subsequent quenching with electrophiles leads to the usual alkylated or functionalized species ... 

The concept of a diastereoselective Friedel-Crafts alkylation of a-chiral benzyl alcohols was first examined by Bach and coworkers [62, 63]. The initial protocol required stoichiometric amounts of strong Brpnsted acids like HBF4 and was followed by a more valuable methodology in which catalytic amounts of AuC L were employed for the diastereoselective functionalization of chiral benzyl alcohols [64], Beside arenes, allyl silanes, 2,4-pentanediones and silyl enol ethers have been used as nucleophiles. Depending on the diastereodiscriminating group and on the catalyst (Brpnsted or Lewis acid), the authors observed either the syn or the anti diastereoisomer as the major product. 

The involvement of transition metal peroxo species in the oxidative functionalization of alkanes and arenes has been postulated for several metals with both hydrogen peroxide and alkyl hydroperoxides. 

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