Acrylate radical addition with

In the case of electron-deficient monomers (e.g, acrylics) it is accepted that reaction occurs by initial addition of the sulfate radical anion to the monomer. Reactions of sulfate radical anion with acrylic acid derivatives have been shown to give rise to the sulfate adduct under neutral or basic conditions but under acidic conditions give the radical cation probahly by an addition-elimination process. 

Thiol-ene polymerization was first reported in 1938.220 In this process, a polymer chain is built up by a sequence of thiyl radical addition and chain transfer steps (Scheme 7.17). The thiol-ene process is unique amongst radical polymerizations in that, while it is a radical chain process, the rate of molecular weight increase is more typical of a step-growth polymerization. Polymers ideally consist of alternating residues derived from the diene and the dithiol. However, when dienes with high kp and relatively low A-, monomers (e.g. acrylates) are used, short sequences of units derived from the diene are sometimes formed. 

Pringle reported that ethyl acrylate also reacts similarly [14]. The radical addition at 70 °C forms a mixture of primary PH2 (CH2CH2COOEt), secondary PH(CH2CH2COOEt)2 and tertiary phosphines. The tertiary phosphine component is not pure P(CH2CH2COOEt)3, but a mixture with telomers. However, Pt complex-catalyzed addition is very clean when PH3 is bubbled through a warmed solution of ethyl acrylate in the presence of 0.002 equiva-... 

Rates of radical additions to alkenes are controlled mainly by the enthalpy of the reaction, which is the origin of regioselectivity in additions to unsymmetrical systems, with polar effects superimposed when there is a favorable match between the electrophilic or nucleophilic character of the radical and that of the radico-phile. For example, in the addition of an alkyl radical to methyl acrylate (2), the nucleophilic alkyl radical interacts favorably with the resonance structure 3. Polar effects are apparent in the representative rate constants shown in Figure 4.14 for additions of carbon radicals to terminal alkenes. Addition of the electron-deficient or electrophilic rert-butoxycarbonylmethyl radical to the electron-deficient molecule methyl acrylate is 10 times as fast as addition of... 

Thioethers have also been prepared on cross-linked polystyrene by radical addition of thiols to support-bound alkenes and by reaction of support-bound carbon radicals (generated by addition of carbon radicals to resin-bound acrylates) with esters of l-hydroxy-l,2-dihydro-2-pyridinethione ( Barton esters Entry 6, Table 8.5). Additional methods include the reaction of metallated supports with symmetric disulfides (Entries 7-9, Table 8.5) and the alkylation of polystyrene-bound, a-lithiated thioani-sole [65],... 

Acyl selenides serve as acyl radical precursors when treated with tin radicals [43], In the following reaction (Scheme 6.25), a cydoheptanone fused to an indanol skeleton is prepared via a three-component reaction [44], The sequential addition of an acyl radical to two molecules of methyl acrylate followed by a 7-endo-type radical addition account for the annulation. 

Pentadienyl-terminated poly(methyl methacrylate) (PMMA) as well as PSt, 12, have been prepared by radical polymerization via addition-fragmentation chain transfer mechanism, and radically copolymerized with St and MMA, respectively, to give PSt-g-PMMA and PMMA-g-PSt [17, 18]. Metal-free anionic polymerization of tert-butyl acrylate (TBA) initiated with a carbanion from diethyl 2-vinyloxyethylmalonate produced vinyl ether-functionalized PTBA macromonomer, 13 [19]. 

Other trialkyltin-containing monomers such as 3-tributyltinstyrene (84), tributyltin methacrylate (85) and 4-[bis(trimethylstannyl)methyl]styrene (86) were also reported to homo- and copolymerise with styrene under radical conditions175-177. In addition, 3-tributyltinstyrene (84) was copolymerised under radical conditions with ethyl acrylate, methyl methacrylate, vinyl acetate and acrylonitrile175. A functional methacrylate-based polymer was prepared by the copolymerization of the triorganotin methacrylate monomer 87 with styrene and divinylbenzene178,179. 

Treatment of O-acyl esters (2) with l,l-dichloro-2,2-difluoroethylene provides a,a-difluorocarboxylic acids (37) through photolysis, followed by the hydrolysis of the adducts (36) with AgN03 (eq. 8.17) [53]. Eq. 8.18 shows the preparation of a-keto carboxylic acids (40) from carboxylic acids, by means of the radical addition to ethyl acrylate, oxidation to the sulfoxides by mCPBA, the Pummerer reaction with... 

In comparison to the cyclization reactions shown above, intermolecular Meerwein arylations are often more difficult to conduct. Since the aryl radical addition to the alkene is no longer favored by the close proximity of the reacting centers, the probability for a direct recombination of the aryl radical with scavengers Y is significantly increased (Scheme 17). To maintain the desired reaction course from 44 to 45 including steps (1) and (2) [89, 90], Meerwein arylations have for a long time mostly been conducted with activated alkenes, such as acrylates (R = COOR ), vinylketones (R = COR ), styrenes (R = Ph), or conjugated dienes [91,92]. These types of alkenes are known for fast addition of aryl radicals. 

Cobalt complexes derived from Schiff bases 388 catalyzed the hydroxyacylation of electron-deficient alkenes (Fig. 90) [431, 432]. Thus, methyl acrylate 387 reacted with aliphatic aldehydes 386 in the presence of 5 mol% of the in situ generated catalyst, molecular oxygen, and acetic anhydride to 2-acyloxy-4-oxoesters 389 in 56-77% yield. When acetic anhydride was omitted, the yields of products were lower and mixtures of the free hydroxy compounds and acylated compounds resulting from Tishchenko reactions were obtained. Electron-rich alkenes did not undergo the transformation, since the addition of the acyl radical is much slower. The acylcobalt species inserts oxygen instead and acts as an epoxidation catalyst. 

Another report has dealt with thioamides involved in radical addition [193]. Substrates bearing an a-cyclopropyl group were transformed into cyclopentyl thioamides by thiophilic addition of a trimethytin radical, opening of the three membered ring, addition of the formed radical to an alkyl acrylate, and cyclisation. 

The copolymerization of furan and 2-methylfuran with dienophiles such as maleic anhydride leads to polymer structures with furan pendent functionality. Furan, 2-methylfuran, and 2,5-dimethylfuran have been copolymerized with acrylic monomers (51,52) and acrylonitrile (52,53). The furan ring of furan, 2-methylfuran, and 2,5-dimethylfuran participates as a diene in a free radical copolymerization with acrylonitrile. The initial step for furan and for 2,5-dimethylfuran is the attachment of an acrylonitrile radical at the 2-position, but for 2-methylfuran, the attack is at the-5-position. Propagation proceeds by the attack of the furan radical on an acrylonitrile molecule, to leave one olefinic bond in the structure derived from the furan ring. If this bond is in the 4,5- or 2,3-position, it may be involved in a second additional reaction by the return of the propagating chain. 

Benzindolizidine systems 963 are generated in moderate yields by a hexabutylditin-mediated consecutive radical addition, cyclization, and oxidation process from easily accessible l-(2-iodoethyl)indoles 962 and methyl acrylate, in one step (Scheme 186) <2000TL10181>. l-(2-Iodoethyl)-l//-pyrrole-2-carbaldehyde was also subjected to the tandem radical addition-cyclization process, and the indolizidine derivative 964 was isolated in modest yield as the major product together with a small amount of starting material (Equation 229). 

R)- and (S)-f-Butyl-5-methylene-l,3-dioxolan-4-one, a Chiral a-Alkoxy Acrylate. It is also possible to introduce an ex-ocyclic double bond onto the dioxolanone ring, as in compounds (9)-(ll), derived from lactic and malic - acids. These a,3-unsaturated carbonyl derivatives are acceptors for radical additions and undergo cycloadditions with dienes and heterodienes. The Diels-Alder adduct (12) of ent-(9) with cyclopentadiene is formed with exo selectivity (96 4) and serves as aprecursor to norbomenone (13). Cycloadduct (14), obtained from methylenedioxolanone (9) and an open-chain triene, is also the result of an exo addition and is used in tetronolide synthesis. ... 

Highly diastereoselective allylations were also achieved in a slightly different manner through radical addition to chiral oxazolidinone acrylate and trapping with allylstannane [25]. In reactions with a,yS-unsaturated substrates, the Lewis acid... 

Table 1 displays rate data for alkoxyamine-termi-nated polymers and low molecular model compounds and shows some important trends. At about the same temperature, the dissociation rate constants Ad of alkoxyamines (Schemes 12 and 30) with the same leaving radical (polystyryl, 1-phenylethyl) increase in the order 3 (TEMPO) < 6 < 8 (DEPN) < 1 (DBNO) by a factor of about 30. Acrylate radicals dissociate markedly slower than styryl radicals from 1 (DBNO), but there is no appreciable difference for 8 (DEPN). The dependence of Ad on the nitroxide structure has been addressed by Moad et al.104 They found the order five membered ring < six membered ring < open chain nitroxides and pointed out additional steric (compare 3 and 6) and polar effects. 

---