Vinyl ethers and esters

Limited work has revealed that vinyl and allyl halides cyclize only in low yield, and the products suffer halogen loss in the process. Also, unlike allyl ethers, vinyl ethers and esters are only marginally... 

Living cationic polymerization techniques are also capable of producing well defined star-block copolymers. An approach similar to the DVB method described above for the case of anionic polymerization was employed in order to prepare amphiphilic star-block copolymers [20]. In one case, living diblock copolymers of vinyl ethers and ester-containing vinyl ethers, prepared by the initiating system Hl/Znh in toluene, were reacted with a small amount of a difunctional vinyl ether to produce star shaped block copolymers (Scheme 5). 

Vinyl ethers and esters From readily available ROCH=CH2 and through an exchange reaction catalyzed by (Ph3P)AuCl-AgOAc a great variety of vinyloxy compounds are prepared. 

Simple alkencs that do undergo the Diels-Alder reaction include conjugated carbonyl compounds, nitro compounds, nitriles, sulfones, aryl alkenes, vinyl ethers and esters, haloalkenes, and dienes. In addition to those you have seen so far, a few examples are shown in the margin. In the last example it is the isolated double bond in the right-hand ring that accepts the diene. Conjugation with the left-hand ring activates this alkene. But what exactly do we mean by activate in this sense We shall return to that question in a minute. 

Simple alkenes that do undergo the Diels-Alder reaction include conjugated carbonyl compounds, nitro compounds, nitriles, sulfones, aryl alkenes, vinyl ethers and esters, haloaUc-... 

Exchange Reactions of Vinyl Ethers and Esters. Vinyl ethers are activated by Pd. Exchange with other alcohols to give mixtures of acetals and vinyl ethers is catalyzed by PdC (eq 41). This reaction was used as the key step in the total synthesis of rhizobitoxine (eq 42). ... 

Addition of nucleophiles to both activated and unactivated alkenes is catalyzed by Pd(II). Addition of alcohols or AcOH to alkenes bearing EWGs is catalyzed by PdCl2(PhCN)2 to give the corresponding ethers and esters. The addition of an alcohol to the cyclic acetal of acrolein 82 to give the ether 83 is also possible with the same catalyst[64]. Amines add to the vinylic ether 84 to give 85, but not to simple alkenes[65]. 

Vinylation. Acetylene adds weak acids across the triple bond to give a wide variety of vinyl derivatives. Alcohols or phenols give vinyl ethers and carboxyHc acids yield vinyl esters (see Vinyl polymers). 

It is possible to treat ketones with allyl alcohol and an acid catalyst to give y,5-unsaturated ketones directly, presumably by initial formation of the vinylic ethers, and then Claisen rearrangement.In an analogous procedure, the enolates (126) of allylic esters [formed by treatment of the esters with lithium isopropylcyclohex-... 

Both ( )-l-phenylsulfonyl and (5)-(+)-3-p-tolylsulfmyl -alk-3-en-2-ones can exhibit high diastereoselectivity in their reactions with vinyl ethers and styrenes, with the dienophile having a dominant influence on the stereochemical outcome <96T1205,96TL3687>. Indol-2-ylideneacetic acid esters can act as both dienophile and heterodiene in cycloaddition reactions in the latter case pyrano[3,2-h]indoles are formed <96SYN519>. 

Another important type of reactivity of palladium, namely oxidative addition to Pd(0), is the foundation for several methods of forming carbon-carbon bonds. Aryl126 and alkenyl127 halides react with alkenes in the presence of catalytic amounts of palladium to give net substitution of the halide by the alkenyl group. The reaction, known as the Heck reaction,128 is quite general and has been observed for simple alkenes, aryl-substituted alkenes, and substituted alkenes such as acrylate esters, vinyl ethers, and A-vinylamides.129... 

Vinyl ethers and vinyl esters are not employed extensively in organic transformations. During the synthesis of phlegmarine, however, the stereogenic center at C-10 was to be introduced stereoselectively by catalytic hydrogenation-hydrogenolysis of the vinyl triflate (Scheme 4.7). 

The most characteristic and useful reaction is the dimerization with incorporation of certain nucleophiles. It is well-known that simple olefins coordinated by Pd2+ compounds undergo nucleophilic substitutions [Eq. (9)] or addition reactions [Eq. (10)] (16, 17). Water, alcohols, and carboxylic acids are typical nucleophiles which attack olefins to form aldehydes, ketones, vinyl ethers, and vinyl esters. 

The hydrogenation is usually limited to nonpolar alkenes (terminal and internal cyclic and acyclic alkenes), even though Ti systems have been used to hydrogenate alkenes containing ether and ester functionalities such as vinyl ethers or methyl oleate [42, 45, 59, 62]. 

The first stage of the polymerisation is again the formation of the ester PjD with complete consumption of D such that [PjD] = [D]0, e.g., CH3CHIOR from HI + alkyl vinyl ether, and the complexation of the monomer M by the acceptor A ... 

Monomers that copolymerize with thiocarbonyl fluoride include olefins, vinyl halides, vinyl esters, ally esters, acrylates, vinyl ethers, and vinyltrichloro-silane. Nonconjugated diolefins lead to crosslinked products. Conjugated dienes inhibit polymerization. 

When using a suitable type I photoinitiator, e.g., acylphosphine oxides and non-amine-containing acetophenones in this system, the polymerization process is very efficient and the resulting product is a 1 1 alternating copolymer. This system is susceptible to oxygen inhibition, but to a much lesser extent than acrylate polymerization. An important advantage of this system is its low toxicity. Typical components include a variety of vinyl ethers and unsaturated esters, such as maleate, fumarate, citra-conate, imides (maleimides), or N-vinylformamides. The system is also... 

Enol Ethers and Esters 0-15 O-Alkylation of carbonyl compounds with diazo alkanes 0-17 Transetherification 0-20 Reaction between acyl halides and active hydrogen compounds 0-23 Transesterification 0-24 Acylation of vinylic halides 0-94 Alkylation with ortho esters 0-107 O-Acylation of 1,3-dicarbonyl compounds... 

The second method is the most widely used to prepare optically active vinyl polymers (poly-a-olefins, poly-vinyl-ethers, polyacrylic esters and amides etc.. ... 

The transfer of a carbamate moiety to olefins has been documented only in very few cases, using activated unsaturated substrates. For example, Yoshida and Inoue reported the selective (100%) formation of 1-ethoxyethyl N,N-dialkylcarbamate esters by the reaction of C02 (5 MPa) with ethyl vinyl ether and secondary amines R2NH (R = Me, Et) in the absence of any catalyst (Equation 6.11) [85]. 

Among all remaining monomers, those containing (per)fluorinated side chains such as fluorinated acrylates, vinyl ethers or esters, maleimides and styrenic monomers are also very interesting and have been studied in (co)telo-merisation. Most of them have been previously reviewed [15]. However, they are not mentioned in this chapter. 

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