Vinyl transfer

Among other organosilicon reagents used for cross-couplings, notable ones are commercial vinylsiloxanes, which are useful for vinyl-transfer reactions (81).280... 

A preliminary investigation directed to determine the influence of the substituents in both the telluride and the starting cuprate, employing cyclohexenone as substrate, showed that phenylvinyl tellurides are not appropriate as the source of the vinyl copper reagent, since both the vinyl and phenyl groups are transmetallated and add to the enone. This result could be anticipated since both the formed carbanions are sp hybridized. Otherwise, butyl vinyl tellurides undergo exclusive Te/vinyl transmetallation followed by the desired vinyl transfer. 

The mechanism of the Petasis boronic acid-Mannich reaction is not fully understood. In the first step of the reaction, upon mixing the carbonyl and the amine components, three possible products can form iminium salt A, diamine B, and a-hydroxy amine C. It was shown that preformed iminium salts do not react with boronic acids. This observation suggests that the reaction does not go through intermediate A. Both intermediate B and C can promote the formation of the product. Most likely, the reaction proceeds through intermediate C, where the hydroxyl group attacks the electrophilic boron leading to an ate -complex. Subsequent vinyl transfer provides the allylic amine along with the boronic acid sideproduct. 

R.A. Batey and co-workers developed a modification of the Petasis-boronic acid-Mannich reaction that occurs via N-acyliminium ions derived from A/-protected-2,3-dihydroxypyrrolidine and 2,3-dihydroxypiperidine derivatives. This method was utilized in the total synthesis of (+)-deoxycastanospermine. The formation of the A/-acyliminium ion was achieved by treating A/-Cbz-2,3-pyrrolidine with BF3-OEt2. ° Subsequent vinyl transfer from the alkenylboronic ester provided the product with excellent yield and diastereoselectivity. 

In the case of 53, a chair-like pre-transition state conformer 53a is thought to be involved, in which the bulky aryl and palladium groups are pseudo equatorial. This gives rise to the energetically most favourable equatorial conformer 53b, which is transformed into 54a (Scheme 5.6.16). Under identical conditions, in the presence of vinyltri-n-butyltin, the intermediate 53a is intercepted by vinyl transfer (Scheme 5.6.16) showing that this inter-molecular anion capture 54b is significantly faster than the 6-exo-trig cyclization-anion capture. 

Intramolecular vinyl transfer from a vinyl ether to an ester has been reported. ... 

A-Alkyl-a,a-dichloroaldimines, for example, A-propyl (40), undergo Lewis-acid-catalysed vinyl transfer, using a terminal alkyne as vinyl donor, yielding geometrically... 

SCHEME 3.122 Synthesis of enamides through vinyl transfer reactions [130]. 

An interesting approach to the preparation of enamides entailed a formal vinyl transfer from vinyl ethers (Scheme 3.122) [130]. The reaction was catalyzed by palladium complexes bearing a phenanthroline derivative as the solubilizing/stabilizing ligand. Several secondary amides including cyclic and acyclic substrates were screened, and... 

Denmark and Wang have shown how hydrosilylation can install a silyl group that can be activated by fluoride via hypervalent intermediate 14.14 so as to act like a boronic acid does in the Suzuki-Miyaura coupling. After vinyl transfer from 14.14 to Pd, reductive elimination with an aryl group from the Arl coreactant gives net addition of Ar-H across a C=C triple bond (Eq. 14.7). 

Scheme 5-183. A palladium catalyzed vinyl transfer—Claisen...

Scheme 5 Palladium-catalyzed vinyl transfer reaction...

FLUORINECOMPOUNDS,ORGANIC - POLY(VINYL FLUORIDE)] (Vol 11) TED. See Transferred electron devices. 

Fig. 4. Chemistry of poly(vinyl cinnamate) negative-acting resist. Initial light absorption by the photosensitizer is followed by energy transfer to produce a pendant cinnamate group in a triplet electronic state. This combines with a second cinnamate on another polymer chain, forming a polymer—polymer...

An example of a commercial semibatch polymerization process is the early Union Carbide process for Dynel, one of the first flame-retardant modacryhc fibers (23,24). Dynel, a staple fiber that was wet spun from acetone, was introduced in 1951. The polymer is made up of 40% acrylonitrile and 60% vinyl chloride. The reactivity ratios for this monomer pair are 3.7 and 0.074 for acrylonitrile and vinyl chloride in solution at 60°C. Thus acrylonitrile is much more reactive than vinyl chloride in this copolymerization. In addition, vinyl chloride is a strong chain-transfer agent. To make the Dynel composition of 60% vinyl chloride, the monomer composition must be maintained at 82% vinyl chloride. Since acrylonitrile is consumed much more rapidly than vinyl chloride, if no control is exercised over the monomer composition, the acrylonitrile content of the monomer decreases to approximately 1% after only 25% conversion. The low acrylonitrile content of the monomer required for this process introduces yet another problem. That is, with an acrylonitrile weight fraction of only 0.18 in the unreacted monomer mixture, the low concentration of acrylonitrile becomes a rate-limiting reaction step. Therefore, the overall rate of chain growth is low and under normal conditions, with chain transfer and radical recombination, the molecular weight of the polymer is very low. 

Tetiafluoioethylene—peifluoiopiopyl vinyl ethei copolymeis [26655-00-5] aie made in aqueous (1,2) oi nonaqueous media (3). In aqueous copolymerizations water-soluble initiators and a perfluorinated emulsifying agent are used. Molecular weight and molecular weight distribution are controlled by a chain-transfer agent. Sometimes a second phase is added to the reaction medium to improve the distribution of the vinyl ether in the poljmier (11) a buffer is also added. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Although most aromatic modified C-5 resins are typically higher softening point resins, certain appHcations, such as adhesives, require lower softening points. Copolymerization of a C-8—C-10 vinyl aromatic fraction with piperylenes in the presence of a C-4—C-8 mono-olefin chain-transfer stream yields resins with softening points ranging from 0—40°C (44). A particular advantage of these Hquid resins is the fact that they eliminate the need for plasticizers or oils in some pressure sensitive adhesive appHcations. 

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