Styrene substitution reaction

In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, selenophene[233,234], and cyclobutadiene iron carbonyl complexpSS] react with alkenes to give vinyl heterocydes. The ease of the reaction of styrene with sub.stituted benzenes to give stilbene derivatives 260 increases in the order benzene < naphthalene < ferrocene < furan. The effect of substituents in this reaction is similar to that in the electrophilic aromatic substitution reactions[236]. 

In addition to providing fully alkyl/aryl-substituted polyphosphasenes, the versatility of the process in Figure 2 has allowed the preparation of various functionalized polymers and copolymers. Thus the monomer (10) can be derivatized via deprotonation—substitution, when a P-methyl (or P—CH2—) group is present, to provide new phosphoranimines some of which, in turn, serve as precursors to new polymers (64). In the same vein, polymers containing a P—CH group, for example, poly(methylphenylphosphazene), can also be derivatized by deprotonation—substitution reactions without chain scission. This has produced a number of functionalized polymers (64,71—73), including water-soluble carboxylate salts (11), as well as graft copolymers with styrene (74) and with dimethylsiloxane (12) (75). 

Furthermore, for the first time this procedure has been extended to (i-ketoesters, although only an intramolecular reaction was feasible. However, with 5 mol% of Bi(OTf)3, the styrene-substituted ketoester 41 was converted into the 2,3-disubsti-tuted cyclohexanone 42 in 72% yield (Scheme 32). 

The olefinic substitution reaction may also be effected in some instances by using a palladium(II) salt and an aromatic compound instead of an organic halide. Palladium(II) salts are apparently able to metallate some aromatic hydrocarbons directly. The reaction succeeds best with aromatics activated with electron-supplying substituents producing, with certain olefinic compounds, vinylically substituted products. For example, benzene and styrene with palladium acetate in boiling acetic acid produce stilbene in 90% yield (37). 

Silver acetate has a small catalytic effect on the alkene substitution reaction but 5 equiv. of the salt only give 140% of stilbene in the styrene phenylation, based upon palladium.15 The same reaction carried out at 80 C under 300 lbf in-2 (1 lbf in-2 = 6.89 kPa) of oxygen gives stilbene in 248% yield, based upon palladium.16 The best reoxidation reagent is f-butyl perbenzoate, which yields 10-14 turnovers of the palladium in the vinyl substitution of cinnamaldehyde and similar alkenes with benzene.17... 

One organic group is readily transferred from tetraorganosilanes (and some other silanes) to palladium ). Tetramethylsilane, lithium tetrachloropalladate(II) and styrene at 120 C in acetonitrile solution form 1 -phenyl- 1-propene in 65% yield along with ca. 1.5% 2-phenyl-1-propene.33 Trimethylphenylsil-ane transfers phenyl and with styrene under the above conditions gives fra/w-stilbene in 94% yield.33 Similar vinyl substitution reactions have been achieved with potassium ( )-alkenyl pentafluorosili-cates.34... 

Chlorotropone, apparently, is the only example of a vinyl-type chloride which is known to undergo the substitution reaction. This chloride and styrene with triethylamine gives a 25% yield of 2-styryltro-pone (equation 33).89... 

The n-arylpalladium bonds in these complexes are reactive and undergo insertion and substitution reactions. The reactions offer useful methods for regiospecific functionalization of aromatic rings, although the reactions are difficult to make catalytic in most cases. Insertion of styrene to AA-dimcthylbcnzylaminc complex (180) to form the stilbene derivative 185 occurs smoothly at room temperature in AcOH [5]. The reaction has been extended to the functionalization of the dopamine analogue (A,A-dimethyl-2-arylethylamine) 187 via the six-membered o/Y/zo-palladated complex 186 [118]. 

Stage (5.6) is distinguished from common radical substitution reactions (including stage (5.8)) by simultaneous transfer of two hydrogen atoms (or H+ + e) from two neighboring carbon atoms (in ethylbenzene molecule) to HO2 free radical via hexasite transition state (I) formed (according to (5.6) this state dissociates to two stable compounds, currently styrene and water) ... 

Bimetallic complexes, such as RuPt(CO)5(PPh3)3, have been immobilized on phosphinated poly(styrene-divinyl-benzene) by a similar hgand-substitution reaction (equation 10). The resulting supported bimetallic complexes have been characterized by IR spectroscopy and are found to act as ethylene Hydrogenation catalysts. 

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