Coupling yielding vinyl ethers

Intermolecular coupling of a vinyl ether with styrene at a carbon anode in methanol is successful, giving a mixture of the cross coupled product and the two homocoupled products [49], Intramolecular coupling between an enol ether and an alkene centre, as in 24 and 25, proceeds to give the cyclized product in good yield [50], Five and six membered rings can be constructed in this way. An easily oxidised vinyl ether group is necessary to initiate the reaction and the second alkene... 

In addition to the effect of the experimental conditions, the influence of the nature of the arms and of the divinyl compound was also studied. It was shown that bulkiness of the arms strongly influences the yield of star polymer for instance, arms of poly(cetyl vinyl ether) were linked in very low yield as compared with poly(IBVE). The influence of the structure of the divinyl ether was investigated and appears to be of great importance. Coupling with 3 and 4 led to low yield of star polymer, while the efficiency of 1 and 2 was much higher. The explanation provided by the authors was that compact and flexible spacers between the two vinyl groups of 3 and 4 could lead to smaller cores where further reaction of incoming chains would be sterically hindered. 

Pd(dba)2 followed by acid hydrolysis gives 8-acetylquinoline <2001T2507>, but utilizing -butyl vinyl ether as coupling partner in a Heck reaction gives 8-acetylquinoline 644 in a better yield. 

Substituted 3-aminofuran-2-carboxylate esters can be prepared following a simple two-step procedure (Scheme 10) <20000L2061>. n-Cyano ketones are coupled with ethyl glyoxylate under Mitsunobu conditions to provide a-cyanovinyl ethers in good yield. Subsequent treatment of the vinyl ether with sodium hydride affords the 3-aminofuran. It was found that carrying out the reaction sequence in a one-pot procedure afforded the 3-aminofuran in comparable yields. 

Simple allylic alcohols and vinyl ethers can be coupled to give 2-alkoxytetrahydrofurans employing a Pd(ii)/Cu(ii) catalyst system under an oxygen atomosphere (Equation 101) <2006SL3110>. The reaction is stereospecific in that the (Z)-cinnamyl alcohol leads to the double-bond geometrical isomer of the product depicted in Equation (101) in 82% yield. 

Vinylic ethers (44) can be synthesized in high yields by the cross-coupling of aryl or benzyl halides with tris(2-ethoxyvinyl)borane (4S) in the presence of 1 molej% of a palladium compound such as tetrakis(triphenylphosphine)palladium and a base (Eq. 108) Since vinylic ethers (44) thus obtained can readily be hydrolyzed to aldehydes, this reaction provides a convenient procedure for converting aryl or benzylic halides into the corresponding aldehydes with two more carbon atoms. 

With regard to the preparation of the Zn/Cu couple, several methods have been developed Dibromomethane may be used instead of diiodomethane when a specifically prepared Zn/Cu couple is applied . The use of Zn/Ag couple often gives better results . Ultrasound irradiation of the reaction mixture has been shown to facilitate the reaction . The cyclopropanation of alkenes with diiodomethane and diethylzinc can be carried out in hydrocarbon solvents and is particularly suitable with easily polymerizable olefins such as vinyl ethers . It has been reported that molecular oxygen remarkably promotes the reaction of diiodomethane with diethylzinc and substantially increases the yield of the adducts . A convenient modification which avoids the handling of pyrophoric diethylzinc has been reported . In reaction of olefins which are sensitive to the unavoidably produced zinc iodide (the Lewis acid), the addition of one equivalent of dimethoxyethane (DME) to the solvent has been recommended . Zinc iodide is then precipitated as the 1 1 DME complex as it is formed. Zinc salts, which often complicate the workup of the reaction mixture, can also be removed as precipitates by the addition of pyridine prior to the workup . ... 

Blaser and Spencer used aroyl halides in place of aryl halides, with aroyl chlorides being of specific interest as ubiquitous, relatively cheap compounds ( Blaser reaction ) [24], This latter reaction is normally conducted in aromatic solvents phosphines are not used here as catalyst ligands since they fully inhibit the reaction. In the same way, benzoic acid anhydrides can be used as the aryl source in combination with PdCl2 and catalytic amounts of NaBr [79]. In this reaction, one of the arenes is used in the coupling reaction by elimination of CO, whereas the other benzoate serves as the base. The benzoic acid thus formed can easily be recycled into the anhydride. The use of aryl and vinyl triflates according to Cacchi [25] and Stille [26] extends the scope of the Heck coupling to carbonyl compounds phenol derivatives act via triflate functionalization as synthetic equivalents of the aryl halides. The arylation of cyclic alkenes [27], electron-rich vinyl ethers [28], and allylic alcohols [29] is accessible through Heck reactions. Allylic alcohols yield C-C-saturated carbonyl compounds (aldehydes) for mechanistic reasons (y9-H elimination), as exemplified in eq. (6). 

Kinetic and mechanistic investigations on the NO3 radical oxidation of three vinyl ethers, methyl, propyl and butyl vinyl ethers have been performed in smog chambers (Klotz et ah, 2004, Georges et al, 2004). Analyses were performed using an in situ FTIR device coupled to a multi-reflection White-cell. Rate constants for the oxidation of methyl and propyl vinyl ethers with NO3 were determined using the relative rate technique and/or by a pseudoabsolute rate technique. Rate constants of (4 2) xio and (1.3 0.2) xio cm molecule" s" were obtained for the NO3 oxidation of methyl and propyl vinyl ethers, respectively. Mechanistic experiments also have been performed for methyl, propyl and butyl vinyl ethers. Main oxidation products are formaldehyde, a formate (methyl, propyl or butyl), nitrates and peroxynitrates (Figure 3). Formaldehyde and the formates have been quantified and their formation yields estimated to be around 50 %. 

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