Oxazoline acrylate esters

Radical induced grafting may be carried out in solution, in the melt phase,292 29 or as a solid state process.296 This section will focus on melt phase grafting to polyolefin substrates but many of the considerations are generic. The direct grafting of monomers onto polymers, in particular polyolefins, in the melt phase by reactive extrusion has been widely studied. Most recently, the subject has been reviewed by Moad1 9 and by Russell.292 More details on reactive extrusion as a technique can be found in volumes edited by Xanthos," A1 Malaika and Baker et a 21 7 The process most often involves combining a frcc-radical initiator (most commonly a peroxide) and a monomer or macromonomer with the polyolefin as they are conveyed through the extruder. Monomers commonly used in this context include MAII (Section 7.6.4.1), maleimidc derivatives and malcate esters (Section 7.6.4.2), (meth)acrylic acid and (meth)acrylate esters (Section 7.6.43), S, AMS and derivatives (Section 7.6.4.4), vinylsilancs (Section 7.6.4.5) and vinyl oxazolines (Section 7.6.4.6). 

Many mechanisms had been proposed in the past to rationalize this selectivity (tri-oxanes, perepoxide, exciplex, dipolar or biradical intermediates) however, it is now generally accepted that the reaction proceeds through an intermediate exciplex which has the structural requirements of a perepoxide. This assumption is supported by (a) the lack of stereoselectivity in the reactions with chiral oxazolines and tiglic acid esters (b) the comparison of the diastereoselectivity of dialkyl substituted acrylic esters with structurally similar non-functionalized aUtenes (c) the intermolecular isotope effects in the photooxygenation of methyl tiglate and (d) the solvent effects on regioselectivity. ... 

In an effort to demonstrate the interesting concept of a catalytic chiral auxilliary, Williams and co-workers showed that the oxazoline-substituted acrylate ester 526... 

Asymmetric Aziridination of Alkenes. The copper-catalyzed aziridination reaction can be rendered enantioselective by the addition of chiral ligands. The first example of an enantioselective aziridination of an alkene employed the bis(oxazoline) ligand (4) (R = f-Bu) and copper(I) trifluoromethanesulfonate as the metal catalyst (eq 14). This catalyst system affords the aziridine in 97% yield and 61% ee. Other reports have appeared subsequently regarding the extended scope of this reaction. " Important contributions to this area include the copper/bis-(oxazoline)-catalyzed aziridination of aryl acrylate esters (eq 15) and the copper/bis(imine)-catalyzed aziridination of cyclic cis-alkenes with the bis(imine) ligand (5) (eqs 16 and 17). ... 

Heck Reactions. The Heck reaction is a Pd-catalyzed olefi-nation usually performed between an aryl halide or triflate and an acrylate ester. While phosphines are traditionally used as ancillary ligands, new Pd(dba)2-mediated reactions have been performed with a variety of other ligand types. These include chelating Wheterocyclic carbene/phosphine ligands, benzimidazoles, and quinolinyl oxazolines. Air stable catalysts have been prepared from Pd(dba)2 and sterically hindered thiourea ligands (eq 24). An effective immobilized catalyst has been prepared from Pd(dba)2 and a dendritic phosphine-containing polymer. ... 

Jew and Park achieved a highly enantioselective synthesis of (2S)-a-(hydroxy-methyljglutamic acid, a potent metabotropic receptor ligand, through the Michael addition of 2-naphthalen-l-yl-2-oxazoline-4-carboxylic acid tert-butyl ester 72 to ethyl acrylate under phase-transfer conditions [38]. As shown in Scheme 5.36, the use of BEMP as a base at —60 °C with the catalysis of N-spiro chiral quaternary ammonium bromide le appeared to be essential for attaining an excellent selectivity. 

Poly(2-alkyl oxazoline)s having methacrylate or acrylate end groups were prepared by two methods [182]. a) Living polyoxazoline chains, prepared using methyl p-toluene sulphonate as initiator, were end-capped by reaction with metal salts or tetraalkylammonium salts of acrylic or methacrylic acid or a trialky-lammonium salt or trimethylsilyl ester of methacrylic acid (functional termination). b) The living polymers were terminated with water in the presence of Na2C03 to provide hydroxyl-terminated chains. Subsequent acylation with acry-loyl or methacryloyl chloride in the presence of triethylamine led to the formation of the macromonomers. The procedures are outlined in the following Scheme 51. 

Another highly selective polyaddition is based on the reaction between phenols and oxazolines, which was applied for the synthesis of hb poly(etheramide)s (3-10). The AB2-monomer 2-(3,5-dihydroxyphenyl)-l,3-oxazoline was polymerized thermally at 190 °C in N-methylcaprolactam solution and randomly branched products with a DB of 50% were obtained.Kakodawa et al. used monomer 3-14, namely 2,2-bis(hydroxymethyl) propyl acrylate, for the synthesis of poly(ether ester)s via triphenylphosphine catalysis. The polymers had only low molecular weight, but as they contain phosphonium ions they can be applied in flame-retardant coatings, which can be cured by UV. These materials can also be synthesized via an A2+Bs-approach [vide infra) of tri(acryloy-loxyethyl) phosphate in the presence of piperidine." ... 

In a brief note, a potentially general route to (u-amino-y-keto-esters (227) via alkylation of 2-oxazolin-5-ones with ethyl acrylate or acrylonitrile, has been described. 

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