Amination of styrene

More recently, Beller et al. reported the first example of an oxidative amination of styrenes by secondary amines to give enamines corresponding to an anti-... 

The amination of styrene, however, led to two products (1-phenyl-1-ethylamine and 2-phenyl-l-ethylamine) in a 1 3 ratio [113], indicating that the hydrozirconation was not completely regioselective [114,115]. Since it is well known that hydrozirconation of trisubsti-tuted alkenes places zirconium at the least hindered carbon of the chain by a process involving zirconium migration, this class of alkenes was not investigated [5,116], On the other hand, hydrozirconation/amination of 3-methyl-l,2-butadiene gave an allylic amine. Reaction of the latter could either occur at the terminal carbon or proceed with... 

Hosokawa, Murahashi, and coworkers demonstrated the ability of Pd" to catalyze the oxidative conjugate addition of amide and carbamate nucleophiles to electron-deficient alkenes (Eq. 42) [177]. Approximately 10 years later, Stahl and coworkers discovered that Pd-catalyzed oxidative amination of styrene proceeds with either Markovnikov or anti-Markovnikov regioselectivity. The preferred isomer is dictated by the presence or absence of a Bronsted base (e.g., triethylamine or acetate), respectively (Scheme 12) [178,179]. Both of these reaction classes employ O2 as the stoichiometric oxidant, but optimal conditions include a copper cocatalyst. More recently, Stahl and coworkers found that the oxidative amination of unactivated alkyl olefins proceeds most effectively in the absence of a copper cocatalyst (Eq. 43) [180]. In the presence of 5mol% CUCI2, significant alkene amination is observed, but the product consists of a complicated isomeric mixture arising from migration of the double bond into thermodynamically more stable internal positions. 

Scheme 12 Regioselective Pd-catalyzed oxidative amination of styrene...

Catalyst conditions very similar to those employed in Eq. 42 and Scheme 12 were used recently by Lloyd-Jones, Booker-Milburn, and coworkers to achieve Pd-catalyzed diamination of conjugated dienes with urea nucleophiles (Eq. 44) [181], Both dioxygen and BQ were evaluated as oxidants, and BQ proved to be significantly more effective (Eq. 44). The beneficial effect of BQ probably arises from its ability to promote nucleophihc attack on the intermediate Tt-allyl palladiiun complex (see below. Sect. 4.4). This hypothesis is supported by the observation that the oxidative amination of styrene with urea, which does not undergo the second nucleophilic attack, proceeds equally effectively with both O2 and BQ as the oxidant (Eq. 45). 

Summaries of results of hydroamination mediated with Rh(I) amide complexes584 and comprehensive reviews giving detailed information of the field are available.585-587 Therefore, only the more important relatively new findings are presented here. In most of the transformations reported transition metals are applied as catalysts. The feasibility of the use of tcrt-BuOK was demonstrated in the base-catalyzed amination of styrenes with aniline.588... 

Oxazolidinones were used in an efficient dioxygen-coupled oxidative amination of styrene derivatives using Pd(II) and Cu(II) salts in the presence of a base. These results, see for example compound 218, are remarkable due to the complete inversion of regioselectivity with respect to the same reaction in the absence of base <03JA12996>. 

Oxidative amination of styrenes. Formation of p-aminostyrenes from a mixture of... 

Rhodium catalysts have also found application in oxidative aminations of styrenes. Beller and co-workers observed that numerous styrenes reacted with various kinds of secondary aliphatic amines in the presence of the cationic rhodium complexe [Rh(cod)2]BF4 and PPhs. Regioselectively the corresponding anti-Markovnikov products ( -enamines) were formed [49], While the Markovnikov product was never observed under such conditions, the target enamine was mostly obtained along with hydrogenated olefin, and in some cases even small amounts of hydroaminated products were detected [50],... 

C) Direct O2 aerobic oxidative amination of styrene with Pd(OAc) Et2N... 

Strong Base Anion Exchangers. As ia the synthesis of weak base anion exchangers, strong base resias are manufactured from styrenic as well as acryhc copolymers. Those based on copolymers of styrene and divinylben2ene are chloromethylated and then aminated. These reactions are the same as for the styrenic weakbase resias. The esseatial differeace is the amine used for amination. Trimethyl amine [75-50-3] N(CH2)3, and /V, /V- dim ethyl eth a n ol amine [108-01 -0] (CH2)2NCH2CH20H, are most commonly used. Both form quaternary ammonium functional groups similar to (8). 

The first, and still widely used, polymer-supported ester is formed from an amino acid and a chloromethylated copolymer of styrene-divinylbenzene. Originally it was cleaved by basic hydrolysis (2 N NaOH, FtOH, 25°, 1 h). Subsequently, it has been cleaved by hydrogenolysis (H2/Pd-C, DMF, 40°, 60 psi, 24 h, 71% yield), and by HF, which concurrently removes many amine protective groups. Monoesterification of a symmetrical dicarboxylic acid chloride can be effected by reaction with a hydroxymethyl copolymer of styrene-divinylbenzene to give an ester a mono salt of a diacid was converted into a dibenzyl polymer. ... 

Decomposition in the presence of styrene at 60°C or with a tertiary amine in the presence of methyl methacrylate gives the corresponding ABA active block copolymer or ABBA active block copolymer, respectively. When both active block copolymers are used as polymeric initiators in another vinyl polymerization, an ABCBA type multiblock copolymer is obtained [34]. 

The reaction of ACPC with linear aliphatic amines has been investigated in a number of Ueda s papers [17,35,36]. Thus, ACPC was used for a interfacia] polycondensation with hexamethylene diamine at room temperature [17] yielding poly(amide)s. The polymeric material formed carried one azo group per repeating unit and exhibited a high thermal reactivity. By addition of styrene and methyl methacrylate to the MAI and heating, the respective block copolymers were formed. 

Lithium alkylamides (in situ generated from the amine and either n-BuLi or sec-BuLi) generally give higher yields under milder conditions. Thus, n-BuLi (5%) catalyzes the addition of primary and secondary amines to styrene to afford (-phenethy-lamines in moderate to good yields (e.g., Bq. 4.32) [155]. NH, and PhNHj, however, do not add to styrene under these conditions. a-Methylstyrene and 1,1-diphenyleth-ylene can also be hydroaminated. 

In copolymers containing the styrene sulfonate moiety and maleic anhydride units, the maleic anhydride units can be functionalized with alkyl amine [1411-1416]. The water-soluble polymers impart enhanced deflocculation characteristics to the mud. Typically, the deflocculants are relatively low-molecular-weight polymers composed of styrene sodium sulfonate monomer maleic anhydride, as the anhydride and/or the diacid and a zwitterionic functionalized maleic anhydride. Typically the molar ratio of styrene sulfonate units to total maleic anhydride units ranges from 3 1 to 1 1. The level of alkyl amine functionalization of the maleic anhydride units is 75 to 100 mole-percent. The molar concentrations of sulfonate and zwitterionic units are not necessarily equivalent, because the deflocculation properties of these water-soluble polymers can be controlled via changes in their ratio. 

A recent patent describes the synthesis and catalytic use of Al-containing TUD-1 materials. Some of the reactions demonstrated inclnde hydrogenation of mesitylene (Pt as active metal) and dehydration of 1-phenyl-ethanol to styrene. Several other conceptnal reactions were also described, amongst others the Diels-Alder reaction of crotonaldehyde and dicyclopentadiene and the amination of phenol with ammonia. 

If the more activated alkene 2-vinylpyridine is used in place of styrene with the same catalysts and the same range of substrates, anti-Markovnikoff hydroamination is also found. Thus, N-[2-(2 -pyridyl)ethyl]piperidine was isolated in 53% yield from reaction of 2-vinylpyridine with piperidine in the presence of [Rh(COD)2]+/2PPh3 under reflux. N H addition was observed with other amines, the remaining product in all cases being primarily that from oxidative amination (Table 12). When the catalytic reaction was run in the absence of phosphine, the yield of hydroamination product increased dramatically.171... 

An even simpler protocol for performing nucleophilic substitutions (aminations) and Suzuki reactions in one pot was reported by the Organ group for the generation of a 42-member library of styrene-based nicotinic acetylcholine receptor (nAChR) antagonists (Scheme 6.21) [49]. After considerable experimentation, the authors found that simultaneous nucleophilic displacement and Suzuki coupling could be carried out very effectively by charging the microwave process vessel with the palladium catalyst (0.5 mol% palladium-on-charcoal), the boronic acid [R1B(OH)2], the... 

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