Transvinylation reaction

The transvinylation reaction between carboxylic acids and vinyl acetate presumably follows a course similar to the reaction of vinyl chloride and acetate just described.558... 

The synthesis of monomers derived from fatty acids incorporating end-functions susceptible to classical poly addition reactions has been revived recently and yielded interesting results. Vinyl oleate (VO) and vinyl linoleate (VL) were synthesised by a transvinylation reaction of the corresponding fatty acids with an excess of vinyl acetate (VAc) in bulk using a safe iridium-based catalyst instead of previously used mercury-based counterparts (which are not acceptable today because of safety concerns) [91]. Scheme 4.21 summarises this synthesis in the case of OA. 

Another procedure involves the dehydration of N(2-hydroxyethyl)carbazole [405,406], which is obtained by the reaction of potassium carbazole with ethylene oxide or 2-chloroethanol. Dehydrochlorination of N(2-chloroethyl)carbazole was reported to be a convenient laboratory scale method [407,408]. Several other methods, such as direct vinylation with ethylene catalyzed by PdCl2 [409] or with vinyl chloride [410] and some transvinylation reactions, have been reported. Although a variety of purification techniques have been developed [404], complete elimination of impurities from NVK prepared from coal tar seems to be impossible. NVK from coal tar contains substantial amounts of sulfur compounds as well as a variety of condensed aromatic impurities... 

It is also possible to prepare vinyl ethers by a transvinylation reaction between an alcohol and a vinyl ether as shown in equation (4). The reaction can be catalyzed by palladium(II) complexes [19] and by mercury salts [20-23]. 

This method is especially recommended for the preparation of vinyl ether monomers bearing functional groups that are sensitive to the basic conditions of the vinylation reaction using acetylene. Transvinylation reactions can also be carried out between alcohols and vinyl acetate, a reaction that has been described by Adelman [24] is also being catalyzed by salts of mercury such as mercuric sulfate. 

Alternatively, thermal cracking of acetals or metal-catalyzed transvinylation can be employed. Vinyl acetate or MVE can be employed for transvinylation and several references illustrate the preparation especially of higher vinyl ethers by such laboratory techniques. Special catalysts and conditions are required for the synthesis of the phenol vinyl ethers to avoid resinous condensation products (6,7). Direct reaction of ethylene with alcohols has also been investigated (8). 

The reaction with cyclohexene was highly stereoselective, since 99% syn addition was observed. By contrast, the propargyl ether MeC=20CH2SiMe3 gave a transvinyl iodonium salt [23]. 

It has been shown that it is the vinyl group that is transferred in this reaction, not an alcoholic one as in acid- or alkali-catalyzed transesterification of esters with saturated alcoholic components. With 0-labeled acetic acid in the transvinylation of vinyl-propionate, the labeled oxygen remained completely in the acetate group [68]. 

A frequently used route is the mercury- or acid-catalyzed transvinylation of vinyl ethers with allylic alcohols (Saucy-Marbet reaction)152-154. 

The metal-catalyzed transvinylation of vinylacetates or vinyl ethers with alcohols is initiated by an oxy-metallation reaction. With PdCl2(PhCN)2 as the catalyst and at low temperature, transvinylation takes place exclusively (Scheme 5a). At higher temperatures, acetal formation is observed after an induction period, in addition to precipitation of palladium (Scheme 5b). It is probable that the acetaliza-tion step is catalyzed exclusively by traces of Brpnsted acid (HCl), rather than via proto-de-metallation of a Pd(II) alkyl species [21, 22]. Consequently, a recent report on the protection of primary alcohols as tetrahydropyranyl- (THP-)ethers by addition to 2,3-dihydropyrane in the presence of PdCl2(MeCN)2 as catalyst... 

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