P-methoxystyrene

In a related photoreaction, hexafluorobutadiene forms the [2+4] adduct with p (Al.lV-dimethylamino)styrene in 11% yield, whereas no such adduct could be detected for the same reaction with p-methoxystyrene [124] (equation 104) The analogous thermal reaction at 120 °C leads only to [2+2] adducts... 

Butadiene p-Methoxystyrene Vinyl acetate Vinyl chloride Diethyl maleate Isopropenyl acetate Vinyl chloride... 

Similarly, hydroboration of p-methoxystyrene with HBcat using zwitterionic [(P-P)Rh(//6-catBcat)] ((4), P-P = dppe, dippe) or [(dippe)Rh(r/3-2-IVIc-a 11 y 1)] (dippe= l,2-bis(diisopropylphosphine)ethane) gave 99% of the internal hydroboration product. Complications arose in studying reactions of hindered styrenes due to the appearance of not only the hydroboration products (A and B), but also the dehydrogenative borylation products C and D (Scheme 5).32 The ratio of products was found to be highly catalyst dependent (Table 2).33... 

The QUINAP ligands are highly active for reaction of -substituted vinylarenes, thus, p-methoxystyrene gives the corresponding branched alcohol in 95% yield (57% ee) within 15 min at room temperature. Similarly, a combination of hydroboration/amination using (13) has allowed primary amines to be formed in a one-pot reaction of vinylarenes upon reaction of the B H addition product with MeMgCl/H2N0S03H (Scheme 10).5°... 

Arya et al. used solid phase synthesis to prepare immobilised dendritic catalysts with the rhodium centre in a shielded environment to mimic nature s approach of protecting active sites in a macromolecular environment (e.g. catalytic sites inside enzymes) [51], Two generations PS immobilised rhodium-complexed dendrimers, 6 and the more shielded 7, were synthesised.The PS resin immobilised rhodium-complexed dendrimers were used in the hydroformylation of styrene, p-methoxystyrene, vinyl acetate and vinyl benzoate using a total pressure of 70 bar 1 1 CO/H2 at 45 °C in CH2C12. 

Using styrene as substrate both 6 and 7 could be recycled four times, apparently without loss in activity or selectivity (>99% conversion after 20 hours b l ratio i 18 1). When p-methoxystyrene was used as a substrate the first three cycles did not suffer... 

Fig. 9. Exdplex formation between excited 9-cyanophenanthrene and p. methoxystyrene. Er is the ground-state repulsion energy hv is the emission maximum of the exdplex and Hq the stabilization energy of the exdplex...

For the polymerisation of styrene (SnC -F O-PhNC -CC at 0°) kjkv for anisole was found [85] to be 1.62. It is highly probable that the big difference between this and the value for isobutene reflects mainly the difference between the ps for the two monomers. The very low value of kjkv in the polymerisation of isobutene - or the very large kv of isobutene - accounts for the observation [86] that, whereas styrene polymerising cationically in the presence of preformed poly-p-methoxystyrene will form grafts by reacting with pendent rings, isobutene will not do so. 

Almost any oxygen atom is more basic than almost any isolated olefinic double bond (obvious exceptions are, apparently, p-methoxystyrene [87] and 1-p-methoxyphenyl, 1-phenylethylene [88]). These principles can be illustrated by a few examples. 

Bidentate chiral water-soluble ligands such as (S,S)-2,4-bis(diphenyl-sulfonatophosphino)butane BDPPTS (Fig. 2) or (R,R) 1,2-bis(diphenylsul-fonatophosphinomethyl)cyclobutane have been prepared [25]. Their palladium complexes catalyze the synthesis of chiral acids from various viny-larenes and an ee of 43% has been reached for p-methoxystyrene with the BDPPTS ligand. Furthermore, recycling of the aqueous phase has shown that the regio- and enantioselectivity are maintained and that no palladium leaches. 

In the case of p-methoxystyrene (p-MeOCgH4CH=CH2), the cation-radical ring closure can lead to 1,2-dianisylcyclobntane or 4-anisyl-6-methoxy-3,4-dihydronaphthalene. Thermodynamic simulations show that the former should be favored in the absence of a solvent, whereas the latter product could be stabilized by a polar solvent (O Neil and Wiest 2006). Of course, such a solvent has to be fairly polar and not nncleophilic. 

Graft copolymers of nylon, protein, cellulose, starch, copolymers, or vinyl alcohol have been prepared by the reaction of ethylene oxide with these polymers. Graft copolymers are also produced when styrene is polymerized by Lewis acids in the presence of poly-p-methoxystyrene. The Merrifield synthesis of polypeptides is also based on graft copolymers formed from chloromethaylated PS. Thus, the variety of graft copolymers is great. 

Some branching has been detected in the polymerizations of styrene and anethole (P-methyl-p-methoxystyrene), indicating intermolecular aromatic substitution by a propagating carbocation on the aromatic ring of another polymer chain [Hatada et al., 1980 Kennedy and Marechal, 1982]. 

TABLE 5-7 Effect of Solvent on Cationic Polymerization of p-Methoxystyrene by Iodine at 30 C... 

Some pairs of very strongly electron-donor and electron-acceptor monomers, such as p-methoxystyrene and dimethyl cyanofumarate, undergo spontaneous alternating copolymerizations without any added free-radical initiator, although heat may be required [Hall and Padias, 1997, 2001]. Initiation involves reaction of the comonomer pair to form a diradical,... 

Results of Dulog, Kern et ah, and a few others (27, 31) are summarized in Table I. From the ra values, toward the unsubstituted styrene-peroxy radical, the most reactive styrene—p-methoxystyrene—is three times as reactive as the least reactive, m-nitrostyrene. Thus, the best electron donor shows the highest reactivity (lowest enthalpy of activation) toward the electron-accepting styrene-peroxy radical. The deviations from unity of the rarb products measure the effects of substitution on the selectivity of the peroxy radicals. These products depart more from unity with increasing differences in the electron-donating and accepting properties of the nuclear substituents. The same trends appear within the other styrene combinations. 

Resctions with Alkenes and Aromatics. Unsymmetrically substituted olefins form head-to-head dimers selectively. We mention the classic vinylcarba-zole," vinyl ethers,indenes, and p-methoxystyrene. The regio-chemistry of the addition is compatible with a stepwise mechanism proceeding via a singly linked 1,4-bifunctional radical cation, in which spin and charge are separated (see above). Several dimerizations have quantum yields greater than... 

When DISN reacts with electron-rich styrenes such as p-methoxystyrene, good yields of reduced pyrazines 117, often accompanied by their oxidized forms, are obtained. However, reaction with electron-deficient styrenes like p-fluorostyrene give the 2-amino-3-(2-arylaziridin-l-yl)maleonitriles (118) (72JA3242 84JOC813). 

N.A. n-pentadecane, ethyl cinnamate, ethyl-p-methoxycinnamate, carene, camphene, borneol, p-methoxystyrene.100 Carminative, diuretic, expectorant, pectoral, stimulant. 

Oleostearic acid Oligopeptides Organic acids Qripavine Oxalates Oxalic acid Oxyberberine Oxylenzoic acid p-coumaric acid p-hydroxybenzoic p-methoxystyrene Pachymic acid Paenoiflorin Paeonine Paeonol Paliloleic acid Palmitic acid... 

Fig. 6. Variation of degree of polymerization with monomer concentration p-methoxystyrene-iodine-l,2-dichloroethane [lj]0 = 1.0 X 10 1 mole/1. 1.5 KV/cm O 0 KV/cm. Reproduced, with permission, from Sakurada, Ise, and Ashida Makromol. Chem. 95, I (1966)...

It is interesting to note that this relation was verified for polymerizations of styrene, p-methoxystyrene, and isobutylvinylether with iodine by Kanoh and Higashimura (19). They have demonstrated that the apparent rate constants of termination, propagation, and monomer transfer increased with increasing dielectric constant of solvent, and the rates of the increase for these three rate constants were of the order of Eq. (21). 

In the polymerisation of p-methoxystyrene initiated by cycloheptatrienyl hexachloroantimonate in methylene chloride Goka and Sherrington 67) found... 

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