2- ethyl vinyl ether, cationic

The observation in 1949 (4) that isobutyl vinyl ether (IBVE) can be polymerized with stereoregularity ushered in the stereochemical study of polymers, eventually leading to the development of stereoregular polypropylene. In fact, vinyl ethers were key monomers in the early polymer Hterature. Eor example, ethyl vinyl ether (EVE) was first polymerized in the presence of iodine in 1878 and the overall polymerization was systematically studied during the 1920s (5). There has been much academic interest in living cationic polymerization of vinyl ethers and in the unusual compatibiUty of poly(MVE) with polystyrene. 

Considering the above-mentioned facts, according to which simple diazoketones yield dihydrofurans with ketene acetals but cyclopropanes with enol ethers, one exports an interlink between these clear-cut alternatives to exist, i.e. substrates from which both cyclopropanes and dihydrofurans result. In fact, providing an enol ether with a cation-stabilizing substituent in the a-position creates such a situation The Rh2(OAc)4-catalyzed decomposition of -diazoacetophenone in the presence of ethyl vinyl ether produces mainly cyclopropane 82 (R=H), but a small amount of dihydro-... 

In 1970, a patent by Fukui and coworkers cited the cationic polymerization of ethyl vinyl ether in liquid C02 [85]. In these reactions, SnCl4 or ethyl etherate of boron trifluoride were employed as the catalysts and the polymerizations were conducted for 20 hours at room temperature to conversion of greater than 90% polymer. No molecular weight data or spectra for these polymers were reported in this work. 

It can be synthesized by reaction of a 1 1 molar ratio of ethyl vinyl ether and phenethyl alcohol in the presence of cation exchange resin [141]. It imparts fresh, floral, green notes and is used in fine fragrances as well as in soap, cosmetics and detergents. 

This article reports on the synthesis of photosensitive polymers with pendant cinnamic ester moieties and suitable photosensitizer groups by cationic copolymerizations of 2-(cinnamoyloxy)ethyl vinyl ether (CEVE) (12) with other vinyl ethers containing photosensitizer groups, and by cationic polymerization of 2-chloroethyl vinyl ether (CVE) followed by substitution reactions of the resulting poly (2-chloroethyl vinyl ether) (PCVE) with salts of photosensitizer compounds and potassium cinnamate using a phase transfer catalyst in an aprotic polar solvent. The photochemical reactivity of the obtained polymers was also investigated. 

VNP, and only homopolymer of polyl2-(cinnamoyloxy)ethyl vinyl ether] (PCEVE) was obtained. It seems that the cationic reactivity of the vinyl ether group in VNP was decreased because of the electron attracting nitro group attached at the 4-position on the phenoxide. 

Therefore, most probably, the formation of chrysenes 246 from 2-benzopyrylium salts occurs via the process of a-1 dimerization. At the same time, one cannot exclude the action of anhydrobase 267 as dieno-phile, which leads to its addition to positions 1 and 4 of the initial 2-benzopyrylium cation by analogy with [4 + 2] cycloadditions in reaction with ethyl vinyl ether (Scheme 14) (cf. Section III,D,1). 

Intermolecular addition and addition-cyclization reactions of aminium cation radicals with electron-rich alkenes such as ethyl vinyl ether (EVE) allow an entry into products containing the N—C—C—O moiety of 13-amino ethers 70 or the equivalent of /3-amino aldehydes 71. The mild conditions under which aminium cation radicals are generated from PTOC carbamates makes the reactions described in Scheme 22 possible. In the absence of hydrogen atom donors, the /3-amino ethoxy(2-pyridylthio) acetal 71 was the major product. The mixed acetal can easily be converted... 

Ar-Vinylacctarnides and ethyl vinyl ether can behave as acetaldehyde anion equivalents and under acidic conditions convert 9-hydroxythioxanthene into thioxanthen-9-ylacetaldehyde 354 via dehydration to the cation (Equation 77) <2004JOC584>. 

The dimerization of butadiene, aryl olefins and ethyl vinyl ether is best rationalized by postulating a radical cation 89 (Eq. (174) ) as first intermediate. As the fi -carbon of 89 has the highest free valence, the highest positive charge density and the lowest atom localization energy radical or electrophilic reactions of 89... 

Phenyl- 1,2-dithiolium cation reacts with acetone and ethyl vinyl ether in the following way (Scheme 4).28... 

Most of the reported polyfvinyl ether) macromonomers have been prepared with a methacrylate end group which can be radically polymerized and which is non-reactive under cationic polymerization conditions [71-73]. Generally, the synthesis was based on the use of the functional initiator 30, which contains a methacrylate ester group and a function able to initiate the cationic polymerization of vinyl ethers. Such initiator can be obtained by the reaction of HI and the corresponding vinyl ether. With initiator 30 the polymerization of ethyl vinyl ether (EVE) was performed using I2 as an activator in toluene at -40 °C. The MW increased in direct proportion with conversion, and narrow MWD (Mw/Mn= 1.05-1.15) was obtained. The chain length could be controlled by the monomer to initiator feed ratio. Three poly(EVE) macromonomers of different length were prepared by this method Mn=1200,5400, and 9700 g mol-1. After complete... 

The preparation involves an oxymercuration (Section 3.5.3) of the C=C double bond of the ethyl vinyl ether. The Hg(OAc) ion is the electrophile as expected, but it forms an open-chain cation A as an intermediate rather than a cyclic mercurinium ion. The open-chain cation A is more stable than the mercurinium ion because it can be stabilized by way of oxocarbe-nium ion resonance. Next, cation A reacts with the allyl alcohol, and a protonated mixed acetal B is formed. Compound B eliminates EtOH and Hg(OAc) in an El process, and the desired enol ether D results. The enol ether D is in equilibrium with the substrate alcohol and ethyl vinyl ether. The equilibrium constant is about 1. However, the use of a large excess of the ethyl vinyl ether shifts the equilibrium to the side of the enol ether D so that the latter can be isolated in high yield. 

Aryl cation chemistry allows a double functionalization of vinyl ethers in a three-component reaction, as depicted in Scheme 3.30. In this case, a 3-arylacetal (e.g., 47) was synthesized after the initial addition of the 4-hydroxyphenyl cation onto ethyl vinyl ether, followed by trapping with the nucleophilic solvent MeOH [77]. For related arylation reactions, see Chapter 10. 

B. Living Cationic Polymerization of Ethyl Vinyl Ether with the... 

There is a scant data on the radical behavior of thianthrene radical cation [58]. As pointed out above, thianthrene radical cation couples with radicals. It shows little reactivity toward oxygen but this may be ascribed to its positive charge which should render it an electrophilic radical. It initiates the polymerization of styrene [59,60], a-methyl styrene [59], and ethyl vinyl ether [59,60],but not that of vinyl pyridine [61], vinyltrimethylsilane [59], methyl acrylate [59, 61], or acrylonitrile [59,61 ]. These results can be explained by cationic rather than radical polymerization. 

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