Styrenes couplings

A later report describes AROM/CM of norbomyl alkenes and styrene coupling partners to create asymmetrically functionalized cyclopentanes with alkenyl groups that can be further elaborated. High yields (>98%) of trans (>98) cross metathesis products (predominantly the desired ring-opened, A-B metathesis product) can be achieved using (97a) (equation 22). 

The mechanism of the reaction may involve a cationic nickel hydride associated with a weakly coordinated counterion (4, Scheme 1) as the true catalyst. This species is formed by the Lewis acid-assisted dissociation of the Ni-X bond from the 16-electron phosphine complex 3, coordination of ethylene (or styrene), coupling of the allyl and vinyl moieties, and subsequent 3-hydride elimination [11a]. Insertion of the vinylarene into the Ni-H bond gives a benzylic complex 5, which can be stabilized as an rj -intermediate 5. The coordinately unsaturated 5 can react with ethylene (and possibly not another vinylarene, if the phosphine is sufficiently bulky) to give 6, which can undergo an insertion followed by P-hydride... 

Lewis acid-catalyzed addition of carbonyl compounds to alkenes is an important method for forming new carbon-carbon bonds. Lewis acid-promoted ene and Baylis-Hillman reactions have been well documented. Notably, boron trihalide-mediated aryl aldehyde-styrene coupling reactions proceed in a different way (Scheme 23.17). Boron trihalide acts simultaneously as a Lewis acid and as a reactant to regioselectively produce l,3-dihalo-l,3-diarylpropane (synlanti = 50/50). 

SCHEME 23.18 Plausible mechanism for BXj-mediated aryl aldehyde-styrene coupling. 

Encouraged by the isolation of flnfi-3-halo-l,3-diarylpropanols in low yields from the BCI3-mediated aldehyde-styrene coupling reaction, an investigation was initiated that focused on the feasibility of developing an efficient route to chloropropanol products via a replacement of one or two chlorides... 

The oxidative coupling of alkenes which have two substituents at the 2 posi-tion, such as isobutylene, styrene, 2-phenylpropene, 1,1-diphenylethylene, and methyl methacrylate, takes place to give the 1,1,4.4-tetrasubstituted butadienes 285 by the action of Pd(OAc)2 or PdCF in the presence of sodium acetate[255-257]. Oxidation of styrene with Pd(OAc)2 produces 1.4-diphenylbutadiene (285, R = H) as a main product and a- and /3-acetoxystyrenes as minor pro-ducts[258]. Prolonged oxidation of the primary coupling product 285 (R = Me) of 2-phenylpropene with an excess of Pd(OAc)2 leads slowly to p-... 

Chlorides are inert. However, the reaction ofp-chlorobenzophenone (9) with a styrene derivative proceeds satisfactorily at 150 C by u.sing dippb [l,4-bis(-diisopropylphosphino)butane] as a ligand to give the stilbene derivative 10. However, dippp [l,3-bis(diisopropylphosphino)propane] is an ineffective ligand[13]. On the other hand, the coupling of chlorobenzene with styrene proceeds in the presence of Zn under base-free conditions to afford the cis-stilbene 11 as a main product with evolution of H . As the ligand, dippp is... 

The Li compound 588 formed by the ort/io-lithiation of A. A -dimethylaniline reacts with vinyl bromide to give the styrene derivative 589(433]. The 2-phe-nylindole 591 is formed by the coupling of l-methyl-2-indolylmagnesium formed in situ from the indolyllithium 590 and MgBr2, with iodobenzene using dppb[434]. 2-Furyl- and 2-thienyllithium in the presence of MgBr2 react with alkenyl halides[435]. The arylallenes 592 and 1,2,4-alkatrienes are prepared by the coupling reaction of the allenyllithium with aryl or alkenyl halides[436]. 

The cis thioboration of terminal alkynes with 9-(arylthio)-9-BBN is catalyzed by Pd(Pli3P)4 in the presence of styrene. The product 136 is converted into the vinyl sulfides 137 and 138 by the treatment with MeOH or by Pd-catalyzed cross-coupling with aryl or alkenyl halides using K3PO4 in DMF[68]. No thioboration takes place with internal alkynes. 

Another type of polyol often used in the manufacture of flexible polyurethane foams contains a dispersed soHd phase of organic chemical particles (234—236). The continuous phase is one of the polyols described above for either slab or molded foam as required. The dispersed phase reacts in the polyol using an addition reaction with styrene and acrylonitrile monomers in one type or a coupling reaction with an amine such as hydrazine and isocyanate in another. The soHds content ranges from about 21% with either system to nearly 40% in the styrene—acrylonitrile system. The dispersed soHds confer increased load bearing and in the case of flexible molded foams also act as a ceU opener. 

Polypeptide Synthesis and Analysis. Sihca or controUed-pore glass supports treated with (chloromethyl)phenylethyltrimethoxysilane [68128-25-6] or its derivatives are replacing chloromethylated styrene—divinylbenzene (Merrifield resin) as supports in polypeptide synthesis. The sdylated support reacts with the triethyl ammonium salt of a protected amino acid. Once the initial amino acid residue has been coupled to the support, a variety of peptide synthesis methods can be used (34). At the completion of synthesis, the anchored peptide is separated from the support with hydrogen bromide in acetic acid (see Protein engineering Proteins). 

A different approach, taken by both Monsanto (58) and Gulf Research and Development Company (59), involved the oxidative coupling of two molecules of toluene to yield stilbene. The stilbene is then subjected to a metathesis reaction with ethylene to yield two molecules of styrene. 

Vinyltoluene, comprising a mixture of ca 33% para- and 67% y /i7-methylstyrene, has been marketed for ca 45 yr by Dow Chemical Company and also by Cosden. However, the performance properties of the polymers prepared from the para isomer are not only superior to those of the polymer prepared from the typical mixed isomers, but are generally superior to those of polystyrene (60). This advantage, coupled with a raw material cost advantage over styrene, suggests that i ra-methylstyrene may displace significant amounts of styrene, currendy a 3.2 x 10 t/yr domestic market. 

Dehydrogenation, Ammoxidation, and Other Heterogeneous Catalysts. Cerium has minor uses in other commercial catalysts (41) where the element s role is probably related to Ce(III)/Ce(IV) chemistry. Styrene is made from ethylbenzene by an alkah-promoted iron oxide-based catalyst. The addition of a few percent of cerium oxide improves this catalyst s activity for styrene formation presumably because of a beneficial interaction between the Fe(II)/Fe(III) and Ce(III)/Ce(IV) redox couples. The ammoxidation of propjiene to produce acrylonitrile is carried out over catalyticaHy active complex molybdates. Cerium, a component of several patented compositions (42), functions as an oxygen and electron transfer through its redox couple. 

The product of this reaction (S—B LC) may initiate a further reaction with styrene monomer to give S—B—S LC. This, in turn, can react with an alcohol, ROH, to give S—B—SH + LiOR. Alternatively, S—B LC may react with a coupling agent such as an organohalogen (45) ... 

Fig. 22. Adhesion rating based on flexural sti engths of laminates of poly(styrene) with glass treated with various silane coupling agents vs. solubility parameter of the organo-functional group of the coupling agent. From ref. [117], by permission.

The toughness of interfaces between immiscible amorphous polymers without any coupling agent has been the subject of a number of recent studies [15-18]. The width of a polymer/polymer interface is known to be controlled by the Flory-Huggins interaction parameter x between the two polymers. The value of x between a random copolymer and a homopolymer can be adjusted by changing the copolymer composition, so the main experimental protocol has been to measure the interface toughness between a copolymer and a homopolymer as a function of copolymer composition. In addition, the interface width has been measured by neutron reflection. Four different experimental systems have been used, all containing styrene. Schnell et al. studied PS joined to random copolymers of styrene with bromostyrene and styrene with paramethyl styrene [17,18]. Benkoski et al. joined polystyrene to a random copolymer of styrene with vinyl pyridine (PS/PS-r-PVP) [16], whilst Brown joined PMMA to a random copolymer of styrene with methacrylate (PMMA/PS-r-PMMA) [15]. The results of the latter study are shown in Fig. 9. 

The earliest SIS block copolymers used in PSAs were nominally 15 wt% styrene, with an overall molecular weight on the order of 200,000 Da. The preparation by living anionic polymerization starts with the formation of polystyryl lithium, followed by isoprene addition to form the diblock anion, which is then coupled with a difunctional agent, such as 1,2-dibromoethane to form the triblock (Fig. 5a, path i). Some diblock material is inherently present in the final polymer due to inefficient coupling. The diblock is compatible with the triblock and acts... 

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