Hydroarylation of styrene

An even more attractive version of Friedel-Crafts alkylations is the utilization of alkenes as electrophiles. These reactions profit on the one hand from the versatility and the availability of the starting materials and on the other from the high atom economy [57]. In this respect, in 2006 we presented a convenient iron-catalyzed protocol for the hydroarylation of styrenes (Scheme 6.14) [58]. 

Apart from our work, few publications have appeared so far concerning this type of hydroarylation of styrene. For example, Periana s group described in 2005 the hydroarylation of styrene with benzene using a bis-tropolonato-iridium(III) organ-ometallic complex [59]. However, in contrast to the results above, the linear product (anti-Markovnikov product) was preferentially generated. 

In the presence of BiCU, the hydroarylation of styrenes Ar,C(R)=CH2 with electron-rich arenes ArH afforded Markovnikov adducts Ar C(R)(Ar)Me selectively in good to high yields as a result of the C-H activation of ArH. Under arene-free conditions, the intermolecular hydroarylation of a-substituted styrenes and subsequent intramolecular hydroarylation produced the cyclic dimers of a-substituted styrenes in good yields.122,123... 

Scheme 12.8 Hydroarylation of styrenes using FeCla as a catalyst.

Asymmetric hydroarylation of styrenes and dienes RCH=CH2 with arylboronates ArB(OR)2, catalysed by (5 )-(Pr Box)PdCl2 (7.5 mol%) and Bu OK (5 mol%), can be attained under oxygen atmosphere to produce RCH(Ar)-Me with <75% ee. The competing -elimination is largely suppressed under these conditions. ... 

Cobalt-phosphine and cobalt-carbene catalysts have been developed for the hydroarylation of styrene with (91) via a chelation-assisted C-H bond activation. The regioselectivity can be controlled in favour of the branched (92) or linear product (93) at will by the ligand. Deuterium-labelling studies demonstrated a reversible C-H bond cleavage and alkene insertion steps and reductive elimination as the rate-and regioselectivity-determining step. ... 

The hydroarylation of styrenes is a very useful transformation. Genet and coworkers [70a] were the first to report the Ru-cat2dyzed hydroarylation of styrenes. This group later reported the successful hydroarylation of aromatic ketones and imines with both vinylsilanes and styrenes [70b]. See Figure 4.38 for the Co-cat2dyzed transformation. 

Figure 4.38 Co-catalyzed hydroarylation of styrenes as described by Lee and Yoshikai [73].

Hydroarylation of alkenes is applied to achieve step-growth co-polymerization of aromatic ketones and ct,c< -dienes such as 3,3,6,6-tetramethyl-3,6-disila-l,7-octadiene and 1,3-divinyltetramethyldisiloxane. Co-polymerization of acetophenone and 3,3,6,6-tetramethyl-3,6-disila-l,7-octadiene is catalyzed by Ru species which has been previously activated by treatment with styrene, and a significantly high molecular weight co-polymer, co-poly(3,3,6,6-tetra-methyl-3,6-disila-l,8-octanylene/2-acetyl-l,3-phenylene), is obtained (Scheme 21 ).166... 

Insertion of aUcynes into aromatic C-H bonds has been achieved by iridium complexes. Shibata and coworkers found that the cationic complex [Ir(COD)2]BF4 catalyzes the hydroarylation of internal alkynes with aryl ketones in the presence of BINAP (24) [111]. The reaction selectively produces ort/to-substituted alkenated-aryl products. Styrene and norbomene were also found to undergo hydroarylation under similar condition. [Cp IrCl2]2 catalyzes aromatization of benzoic acid with two equivalents of internal alkyne to form naphthalene derivatives via decarboxylation in the presence of Ag2C03 as an oxidant (25) [112]. 

The Brpnsted acidic anilinium salt [PhNH3+][ B(C6F5)4] has been developed as a catalyst for the hydroamination and hydroarylation of alkenes, such as styrenes, nor-bomene, cyclic alkenes, and cyclohexadiene, with anilines. The weakly coordinating... 

Other C-C bond-forming reactions have been successfully developed using SCCO2 and liquid CO2 as reaction media. Examples include the synthesis of cyclopentenones via cobalt-catalyzed cocyclizations of alkynes with alkenes and carbon monoxide (Pauson-Khand reaction) (Scheme 30) , enantioselective nickel-catalyzed hydrovinylation of styrenes (Scheme 31) , and the palladium-catalyzed hydroarylation of acyclic jS-substimted-o , j8-enones with aryl iodides (formal conjugate addition) (Scheme 32). ... 

Moreover, the efficient bismuth-catalyzed hydroarylation of various styrenes has been recently reported and provides a straightforward access to a series of valuable 1,1-diarylalkane products [129]. Among all the bismuth-based catalysts screened, Bi(0Tf)3 xH20 proved to be the most efficient (Equation 55). 

Using the results of previous studies of palladium- and platinum-catalyzed hydroarylation of alkynes (Fig. 26A), Kitamura and coworkers extended this chemistry to functionahze PS and polystyrene-l)/ocfe-poly(ethylene-ra -butylene)-l>/ocfe-polystyrene (SEES) with acrylic acid moieties (Fig. 26B). Reactions of PS with propionic acid or methyl ester in the presence of K2PtCl4 and Ag(CF3S03) afforded maximums of 7% and 30% alkenylated styrene unit for PS and SEES, respectively. Although... 

Some of the hydroarylation product is also observed substituted anilines afford the two products to varying degrees (Equation (15)). The closely related rhodium complexes [Rh(PCy3)2Cl]2, [Rh(dmpe)Cl]2 (where dmpe= l,2-bis(dimethylphosphino)ethane), and [Rh(C8H14)Cl]2 show essentially no catalytic activity.166 Application of [Rh(PEt3)2Cl]2 to the reaction of aniline with styrene gives a mixture of hydroamination and oxidative amination products, the latter predominating.167 Other related rhodium-catalyzed amination reactions (oxidative amination) have been reported.168 169... 

The Ru(II) catalysts currently used for olefin hydroarylation reactions are limited in terms of incorporation of substituents into the olefin substrate. For example, attempted hydrophenylation of isobutylene with TpRu(CO)(NCMe)(Ph) as catalyst does not yield new organic products. In addition, extension of catalysis to hetero-functionalized olefins using the TpRu(CO)(NCMe)(aryl) systems has not been successful. For electron-deficient olefins (e.g. styrene, methyl methacrylate, acrylonitrile) the TpRu(II) complexes initiate radical polymerization of the olefin in transformations that probably involve a Ru(III/II) redox change [4]. The... 

Representative diene-based polymers include natural rubber (NR), polyisoprene (PIP), PBD, styrene—butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR), which together compose a key class of polymers widely used in the rubber industry. These unsaturated polyolefins are ideal polymers for chemical modifications owing to the availability of parent materials with a diverse range of molecular weights and suitable catalytic transformations of the double bonds in the polymer chain. The chemical modifications of diene-based polymers can be catalytic or noncatalytic. The C=C bonds of diene-based polymers can be transformed to saturated C—C and C—H bonds (hydrogenation), carbonyls (hydrofbrmylation and hydrocarboxylation), epoxides (epoxidation), C—Si bonds (hydrosilylation), C—Ar bonds (hydroarylation), C—B bonds (hydroboration), and C—halogen bonds (hydrohalogenation). ... 

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