Applications ethyl vinyl ether

In an analogous study by Meske, the impact of various oxazaborolidinone catalysts for the 1,3-dipolar cycloaddition reactions between acyclic nitrones and vinyl ethers was studied [31]. Both the diastereo- and the enantioselectivities obtained in this work were low. The highest enantioselectivity was obtained by the application of 100 mol% of the tert-butyl-substituted oxazaborolidinone catalyst 3d [27, 32] in the 1,3-dipolar cycloaddition reaction between nitrone la and ethyl vinyl ether 8a giving endo-9a and exo-9a in 42% and 27% isolated yield, respectively, with up to 20% ee for endo-9a as the best result (Scheme 6.10). 

The above described reaction has been extended to the application of the AlMe-BINOL catalyst to reactions of acyclic nitrones. A series chiral AlMe-3,3 -diaryl-BINOL complexes llb-f was investigated as catalysts for the 1,3-dipolar cycloaddition reaction between the cyclic nitrone 14a and ethyl vinyl ether 8a [34], Surprisingly, these catalysts were not sufficiently selective for the reactions of cyclic nitrones with ethyl vinyl ether. Use of the tetramethoxy-substituted derivative llg as the catalyst for the reaction significantly improved the results (Scheme 6.14). In the presence of 10 mol% llg the reaction proceeded in a mixture of CH2CI2 and petroleum ether to give the product 15a in 79% isolated yield. The diastereoselectiv-ity was the same as in the acyclic case giving an excellent ratio of exo-15a and endo-15a of >95 <5, and exo-15a was obtained with up to 82% ee. 

The preparation of resin-bound nitroalkenes via a microwave-assisted Knoevenagel reaction of resin-bound nitroacetic acid with aryl and alkyl substituted aldehydes is reported. The potential of these resin-bound nitroalkenes for application in combinatorial chemistry is demonstrated by a Diels-Alder reaction with 2,3-dimethylbutadiene (Scheme 8.9). It is also used for one-pot three-component tandem [4+2]/[3+2] reactions with ethyl vinyl ether and styrene 46... 

Apart from these findings, the limited application of ZnCl2 (cyclopropanation of some cyclic 1,3-dienes, isoprene and ethyl vinyl ether 4S-49)) and copper(II) acetyl-acetonate (cyclopropanation of enamines 50)) still stand alone. 

The perfluoroacetamide catalysts, rhodium(II) trifluoroacetamidate [Rh2(tfm)4] and rhodium(II) perfluorobutyramidate [Rh2(pfbm)4], are interesting hybrid molecules that combine the features of the amidate and perfluorinated ligands. In early studies, these catalysts were shown to prefer insertion over cycloaddition [30]. They also demonstrated a preference for oxindole formation via aromatic C-H insertion [31], even over other potential reactions [86]. In still another example, rhodium(II) perfluorobutyramidate showed a preference for aromatic C-H insertion over pyridinium ylide formation, in the synthesis of an indole nucleus [32]. Despite this demonstrated propensity for aromatic insertion, the perfluorobutyramidate was shown to be an efficient catalyst for the generation of isomtinchnones [33]. The chemoselectivity of this catalyst was further demonstrated in the cycloaddition with ethyl vinyl ethers [87] and its application to diversity-oriented synthesis [88]. However, it was demonstrated that while diazo imides do form isomtinchnones under these conditions, the selectivity was completely reversed from that observed with rhodium(II) acetate [89, 90]. 

Recently, the first examples of catalytic enantioselective preparations of chiral a-substituted allylic boronates have appeared. Cyclic dihydropyranylboronate 76 (Fig. 6) is prepared in very high enantiomeric purity by an inverse electron-demand hetero-Diels-Alder reaction between 3-boronoacrolein pinacolate (87) and ethyl vinyl ether catalyzed by chiral Cr(lll) complex 88 (Eq. 64). The resulting boronate 76 adds stereoselectively to aldehydes to give 2-hydroxyalkyl dihydropyran products 90 in a one-pot process.The diastereoselectiv-ity of the addition is explained by invoking transition structure 89. Key to this process is the fact that the possible self-allylboration between 76 and 87 does not take place at room temperature. Several applications of this three-component reaction to the synthesis of complex natural products have been described (see section on Applications to the Synthesis of Natural Products ). 

High-pressure absorption spectroscopy is widely applicable for studying the reactivity and the selectivity of chemical transformations. Some results are shown concerning the investigation of the //ctc/ o-Diels-Alder reactions between the enamine carbaldehyde 1 and enamino ketones 2 with ethyl vinyl ether 3, which lead to the diastereomeric dihydropyrans 4-1-5 and 6 + 7, respectively. Scheme 6.7-1 (Buback et al., 1988 Buback et al., 1989). 

A useful preparative application of enolate oxidation was presented by Torii in the context of a facile synthesis of 4-hydroxyindole 59 [145]. Similar to Schafer s work [114], the anion of 1,3-cyclohexadione was added anodically to ethyl vinyl ether providing products 56 and 57 in 65%. The mixture of both can be transformed by reaction with (NH4)2C03 in methanol into 58 that is finally converted to 59. 

Esterification of dialkyl phosphates is carried out with diethyl azodicarboxylate and triphenylphosphine (equation 46). This condensation is applicable to phosphorylation of pyrimidine nucleosides. The trichloromethanephosphonic acid derivative (69 equation 47) serves as a phosphorylating agent of ribonucleosides, affording the 2 - and 3 -monophosphates. ° Ethyl vinyl ether assisted the dimeric condensation of diethyl hydrogen phosphate giving tetraethyl pyrophosphate (equation 48). ... 

The first example of the successful application of high pressure in the one-pot [4 + 2]/[3 + 2] cycloaddition is the reaction of ethyl vinyl ether (10), yff-nitrostyrene (11) and methyl acrylate (12) (Scheme 9.5). At ambient pressure nitroso acetal (13) was obtained in 43 % yield, after stirring for 20 days using 30 equiv. of enol ether... 

Heterocyclic o-quinodimethanes are unstable and reactive dienes that must be generated in situ. In solution and in the pre.sence of a dienophile the -quinodimethanes can be intercepted in a Diels-Alder reaction, often in high yield. Most of the dienophiles investigated so far have been electron deficient A-phenylmaleiinide. acrylonitrile, methyl vinyl ketone, acrylate, ftimarate and acetylenedicarboxylic esters are typically used. However, since the objective of most of the work was simply to establish that the o-quinodimethane was being formed, the scope of the reaction has not been adequately explored. The pyridine derived o-quinodimethane 12 has recently been shown to undergo cycloaddition to ethyl vinyl ether (Scheme 2) and to dihydroftiran <96T11889>, and it is thus clear that the scope of the Diels-Alder reaction extends beyond electron deficient alkenes and alkynes. Heterodienophiles (azodicarbonyl compounds and nitrosobenzene) have been added to indole-2,3-quinodimethanes <91T192,S> and this type of hetero Diels-Alder reaction is also potentially of wider application. 

A strategy developed by Tietze and coworkers early in his independent career involved the application of intramolecular or intermolecular inverse electron demand hetero-Diels-Alder reactions to iridoid total synthesis. The intermolecular [4+ 2]-cycloaddition of ethyl vinyl ether and unsaturated aldehyde 31 provided acetal 32, which underwent double bond isomerization to afford 33 (Scheme 1) An intramolecular variant of this reaction is discussed in detail later (Scheme 10). More recently, Jacobsen and Chavez extended this work with the enantio- and diastereoselective synthesis of a range of iridoid natural products. Utilizing tridentate Cr(III) catalyst 34, acetal 35 was prepared in 98% ee with good diastereoselectivity (Scheme 1)P... 

As we have already reported, sequential living cationic polymerizations of functionalized vinyl ethers (8) readily give amphiphilic block copolymers (17). Such sequential living polymers are equally applicable to the star polymer synthesis. A typical example utilizes an AB living block copolymer ( ) that consists of 2-(acetoxy)ethyl vinyl ether and IBVE (10 and 30 units per chain, respectively). The... 

Acrylate copolymers produced by emulrion polymerization are being used as elastomers which, after vulcanization, have a combination of heat resistance and oil resistance useful in specialty applications such as gai ts for automatic transmissions in automotive engines. Two t3q>es of copolymers are being used. In one, ethyl acrylate is copolymerized with about 5 per cent of a chloro-containing monomer such as chloroethyl vinyl ether in the other, either ethyl acrylate or butyl acrylate is copolymerized with about 5-15 per cent of acrylonitrile., ... 

The early hot melt adhesives were not strictly definable as rubber-based adhesives. Most rubber polymers such as natural rubber and random SBR are of such molecular weight and structure that they do not melt readily to a workable coating consistency at a temperature below which thermal degradation and decomposition take place. Certain synthetic polymers, however, lend themselves to the formulation of a wide range of hot melt adhesive compositions. Polyamide and polyester resins, ethylene-vinyl acetate (EVA) copolymers, ethylene-ethyl acrylate (EEA) copolymers, low molecular weight polyethylene and amorphous polypropylene, and certain vinyl ethers have found application in hot melt adhesives. These adhesives have found wide use in packaging, industrial, and construction applications. 

A copolymer of ethyl acrylate with 5% chloroethyl vinyl ether has been marketed as an oil-resistant, high-temperature-stable, specialty elastomer. The pendant chlorine group gives a preferred cross-linking site with polyfunctional amines. The relatively high Tg of the rubber (about 28°C) can be lowered by plasticization, but this can be temporary if oils or solvents are in contact with the product and leach out the plasticizer. Interpolymers of ethyl acrylate with methyl methacrylate and with higher acrylates and methacrylates are widely used as latex paints and as additives for paper and textiles. The Tg of an interpolymer can be tailored for a particular application by varying the ratio of acrylate to methacrylate monomers. 

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