Styrene substituted derivatives

Indan formation is significant in polymerizations of styrene, a-methylstyrene, and p-alkyl-substituted styrenes, but is less important in p-me-thoxystyrene polymerizations [14], Indan formation is not possible in polymerizations of styrene derivatives substituted at both ortho positions and is suppressed in polymerizations of 3,5-disubstituted styrene derivatives due to steric hindrance [105]. Indan formation consumes initiator in attempts at polymerizing isobutene with cumyl chloride and p-dicumyl chloride initiators [280]. 

Polymers of Styrene Derivatives. Many styrene derivatives have been synthesized and the corresponding polymers and copolymers prepared (61). Glass-transition temperatures for a series of substituted styrene polymers are shown in Table 3. The highest T is that of... 

A large number of pyridazines are synthetically available from [44-2] cycloaddition reactions. In one general method, azo or diazo compounds are used as dienophiles, and a second approach is based on the reaction between 1,2,4,5-tetrazines and various unsaturated compounds. The most useful azo dienophile is a dialkyl azodicarboxylate which reacts with appropriate dienes to give reduced pyridazines and cinnolines (Scheme 89). With highly substituted dienes the normal cycloaddition reaction is prevented, and, if the ethylenic group in styrenes is substituted with aryl groups, indoles are formed preferentially. The cycloadduct with 2,3-pentadienal acetal is a tetrahydropyridazine derivative which has been used for the preparation of 2,5-diamino-2,5-dideoxyribose (80LA1307). 

Several alkenes are converted to aziridines by treating with oxaziridine (52) at elevated temperatures. Styrene, a-methylstyrene and their derivatives substituted in the benzene ring react smoothly, and so do 1,1-diphenylethylene, indene and acrylonitrile (74KGS1629). 

The traditional means of assessment of the sensitivity of radical reactions to polar factors and establishing the electrophilicity or nucleophilieity of radicals is by way of a Hammett op correlation. Thus, the reactions of radicals with substituted styrene derivatives have been examined to demonstrate that simple alkyl radicals have nucleophilic character38,39 while haloalkyl radicals40 and oxygcn-ccntcrcd radicals " have electrophilic character (Tabic 1.4). It is anticipated that electron-withdrawing substituents (e.g. Cl, F, C02R, CN) will enhance overall reactivity towards nucleophilic radicals and reduce reactivity towards electrophilic radicals. Electron-donating substituents (alkyl) will have the opposite effect. 

A chiral bis(oxazolinyl)phenylrhodium complex was found to catalyze the asymmetric hydrosilylation of styrenes with hydro(alkoxy)silanes such as HSiMe(OEt)2 (Scheme 7).47 Although the regioselectivity in forming branched product 27 is modest, the enantiomeric purity of the branched product 27 is excellent for styrene and its derivatives substituted on the phenyl group. The hydrosilylation products were readily converted into the corresponding benzylic alcohols 29 (up to 95% ee) by the Tamao oxidation. 

The two-substituted-Quinazolinap-derived rhodium complexes proved extremely efficient catalysts for the hydro-boration-oxidation of vinylarenes (Table 6). For styrene derivatives, in most cases quantitative conversions were obtained after just 2 h at the relevant temperature (entries 1-6). Higher enantioselectivities were afforded with a 4-methoxy substituent (up to 95% ee, entry 3) compared to the 4-chloro or unsubstituted styrene analogs (entries 5 and 1), a trend also observed in hydroboration with rhodium complexes of QUINAP 60. This highlights that both the electronic nature of the substrate combined with the inherent steric properties of the catalyst are important for high asymmetric induction. It is noteworthy that in most cases, optimum enantioselectivities were afforded by the... 

For the addition of ethylene, EtOAc as solvent was particularly advantageous and gave 418 in 60% yield (Scheme 6.86). The monosubstituted ethylenes 1-hexene, vinylcyclohexane, allyltrimethylsilane, allyl alcohol, ethyl vinyl ether, vinyl acetate and N-vinyl-2-pyrrolidone furnished [2 + 2]-cycloadducts of the type 419 in yields of 54—100%. Mixtures of [2 + 2]-cycloadducts of the types 419 and 420 were formed with vinylcyclopropane, styrene and derivatives substituted at the phenyl group, acrylonitrile, methyl acrylate and phenyl vinyl thioether (yields of 56-76%), in which the diastereomers 419 predominated up to a ratio of 2.5 1 except in the case of the styrenes, where this ratio was 1 1. The Hammett p value for the addition of the styrenes to 417 turned out to be -0.54, suggesting that there is little charge separation in the transition state [155]. In the case of 6, the p value was determined as +0.79 (see Section 6.3.1) and indicates a slight polarization in the opposite direction. This astounding variety of substrates for 417 is contrasted by only a few monosubstituted ethylenes whose addition products with 417 could not be observed or were formed in only small amounts phenyl vinyl ether, vinyl bromide, (perfluorobutyl)-ethylene, phenyl vinyl sulfoxide and sulfone, methyl vinyl ketone and the vinylpyri-dines. 

The present procedure is applicable only to bromomalononitrile various a-halogen active methylene derivatives, (e.g., diethyl chloromalonate, methyl bromoacetoacetate) led predominantly to the formation of ring-contracted styrene derivatives. On the other hand, substituted cycloheptatrienylium salts with bromomalononitrile gave the desired dicyanoheptafulvene derivatives in excellent yields. One notable example is the synthesis of 5- and 7-(dicyanomethylene)-2,3-dihydrocyclohepta-1,4-dithiins.6... 

Iodine was found to be an efficient catalyst for the aziridination of alkenes (Scheme 6) utilizing chloramine-T (A-chloro-A-sodio-p-toluenesulfonamide) as the nitrogen source. For example, when 2 equiv. of styrene (45a) were added to chloramine-T in the presence of a catalytic amount of iodine (10mol%) in a 1 1 solvent mixture of acetonitrile and neutral buffer, the corresponding aziridine (46) was obtained in 91% yield. The reaction proved to work with other acyclic and cyclic alkenes, such as oct-l-ene and cyclohexene. The aziridination of para-substituted styrene derivatives (45b-e) demonstrated that, as expected for an electrophilic addition, electron-rich alkenes reacted faster than electron-poor alkenes. However, with 1 equiv. of I2, mainly iodohydrin (47) was formed. A catalytic cycle has been proposed to account for the fact that only a catalytic amount of iodine is required (Scheme 1) ... 

In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, seienophene[233,234], and cyclobutadiene iron carbonyl complex[235] react with alkenes to give vinyl heterocycles. The ease of the reaction of styrene with substituted 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]. 

Polymerization of isobutylene, in contrast, is the most characteristic example of all acid-catalyzed hydrocarbon polymerizations. Despite its hindered double bond, isobutylene is extremely reactive under any acidic conditions, which makes it an ideal monomer for cationic polymerization. While other alkenes usually can polymerize by several different propagation mechanisms (cationic, anionic, free radical, coordination), polyisobutylene can be prepared only via cationic polymerization. Acid-catalyzed polymerization of isobutylene is, therefore, the most thoroughly studied case. Other suitable monomers undergoing cationic polymerization are substituted styrene derivatives and conjugated dienes. Superacid-catalyzed alkane selfcondensation (see Section 5.1.2) and polymerization of strained cycloalkanes are also possible.118... 

Dryanska and Ivanov175 have condensed 2-methylbenzoxazole and 2-methylbenzothiazole (111) with an aryl aldehyde to yield the corresponding substituted styrene derivative 112. Depending on conditions, the intermediate carbinol has been isolated. 

The homogeneous catalytic olefinic substitution, like the carboalkoxylation, does not generally proceed in high yield with aromatic chlorides under the usual conditions. A heterogeneous catalyst, palladium on charcoal, has been reported to cause chlorobenzene and other aromatic chlorides to react with styrene and styrene derivatives, with sodium carbonate as a base at 100° 30, 3]). In our laboratory, we have found the reactions occur as described, but the catalyst is apparently rapidly deactivated. 

Nucleophile addition to styrene derivatives (e.g. 75) coordinated with Cr(CO)3 is another example of addition-electrophile trapping.23,128 Addition of reactive anions is selective at the 3-position of the styrene ligand, leading to the stabilized benzylic anion (76). The intermediate reacts with protons and a variety of carbon electrophiles to give substituted alkylbenzene ligands (in 77) (equation 52). 

Styrene and substituted styrenes react with tetramesityldisilene 1, tetra-tert-butyl-disilene 21, and tetrakis(tert-butyldimethylsilyl)disilene 22 to afford the corresponding disilacyclobutane derivatives.127,134 Similarly, [2 + 2] additions occur between the disilenes with a C = C double bond in an aromatic ring135 and acrylonitrile.136 Bains et al. have found that the reaction of disilene 1 with trans-styrene- provides a 7 3 diastereomeric mixture of [2 + 2] adducts, 201 and 202 [Eq. (95)] the ratio is changed, when czs-styrene-Ji is used.137 The formation of the two diastereomeric cyclic adducts is taken as the evidence for a stepwise mechanism via a diradical or dipolar intermediate for the addition, similar to the [2 + 2] cycloaddition of phenylacetylene to disilene ( )-3, which gives a 1 1 mixture of stereoiso-meric products.116,137... 

On the other hand, PIFA-induced oxidation of p-methoxy-substituted phenols (15) in the presence of electron-rich styrene derivatives (16) resulted in new carbon-carbon bond formation via an intermolecular 1,3-cycloaddition to afford frazzs-dihydrobenzofurans (17) stereoselectively [35,36] [Eq. (4)]. A formal synthesis of neolignans such as kadsurenone (18) and denudatin B (19) was achieved by this methodology. 

A new type of triaryl phosphine-functionalized imidazolium salt containing cations such as (6) has been prepared. Palladium complexes of (6) generated in situ have been used successfully in Heck-type reactions of aryl halides with acrylates and of 4-bromotoluene with styrene derivatives.34 The first Heck-type reaction of aryl halides with allenes has been reported. 1,3-Double arylations were observed with 3-substituted-l,2-allenyl sulfones, while 1-monoarylation was favoured with 3,3-disubstituted-l,2-allenyl sulfones.35 It has been shown that the a-arylation of methane-sulfonamides (7) may be achieved using palladium catalysis reaction proceeds through the sulfonamide enolates.36 It is also reported that palladium cross-coupling of alkynes with /V - (3 - i odophe n y I an i I i ncs) may lead to the formation of substituted carbazoles.37... 

A novel application of dimethylsulfonium methylide for the general preparation of non-readily accessible and synthetically valuable 1-substituted vinylsilanes and styrene derivatives has been developed.55 It has been found that by varying conditions, the reactions can be tuned in either direction to give an alkene or cyclopropane exclusively. 

Addition of dimethylsulfonium methylide (122) to various Michael acceptors (121), followed by alkylation, has been reported to produce functionalized 1-substituted alkenes (124), arising via the unprecedented elimination (123), rather than the usual cyclopropanation products. In silyl substituted substrates, where a facile Peterson-type olefination is possible from the adduct, elimination took place instead. Aryl-substituted Michael acceptors (121 R1 = Ar) underwent a similar olefination to give 1-substituted styrene derivatives with moderate yields along with a side product, which arose by nucleophilic demethylation from the adduct of dimethylsulfonium methylide and arylidene malonates. Hammett studies revealed that selectivity for olefination versus demethylation increases as the aryl substituent becomes more electron deficient.164... 

Syndiotactic polystyrene was first obtained only recently by Ishihara et al. [5] in polymerisation with a homogeneous catalyst derived from a transition metal compound such as monocyclopentadienyltitanium trichloride and methylalu-minoxane in toluene. Since then, several authors have reported on the synthesis of syndiotactic polystyrene promoted by different catalysts based on metal hydrocarbyls such as benzyl compounds, half-sandwich metallocenes (e.g. monocyclopentadienyl, monopentamethylcyclopentadienyl and monoindenyl metal derivatives), metal alkoxides, metallocenes and some other compounds. These catalysts are commonly derived from titanium or zirconium compounds, either activated with methylaluminoxane or aluminium-free, such as those activated with tris(pentafluorophenyl)boron, and promote the syndiospecific polymerisation of styrene and substituted styrenes [5-10,21,48-70], Representative examples of the syndiospecific polymerisation of styrene using catalysts based on various titanium compounds and methylaluminoxane are shown in Table 4.2 [6,52,53,56,58],... 

Photoinduced nucleophilic addition of ammonia and alkylamines to methoxy-substituted styrene derivatives. Tetrahedron, 50, 9275-9286. 

Some p-substituted styrene derivatives were employed in the reaction to establish the generality of the present asymmetric synthesis. The pronounced effect of pyridine IV-oxide was also observed in the aziridination of mms-P-methylstyrene. While this compound was not aziridinated below room temperature in the absence of pyridine IV-oxide, the addition of the N-oxide to the reaction system resulted in both high yield and enantioselectivity of the aziridinated product, even at 0 °C (Table 6.3). 

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