Vinyl side chain

Ring closure of functionalized dienones occurs again in 1,4-fashion to give an annulated six-membered ring. Both Lewis acid (ethylaluminum dichloride) and fluoride ion can be employed, but the chemical yield of this particular cyclization is low and no stereoselection regarding the position of the vinyl side chain was achieved35. 

Catalysts with an unsymmetrical NHC ligand featuring a vinylic side chain have the unique ability to metathesise their own ligand to form a metaUacycle as shown in Scheme 3.7 [119], Ring opening metathesis will then incorporate the monomers, e.g. cyclooctene, into that cycle until a cyclic polymer is cleaved by another intramolecular metathesis step. The catalyst is recovered and can restart this endless route to cyclic polymers [121]. 

Di- or tetrahydropyrans with vinyl side chains obtainable by diastereo-selective ring closing metathesis or by addition of vinylmagnesium chloride to appropriately functionalized tetrahydropyranones are converted to spirocyclic hemiacetals under hydroformylation conditions (Scheme 4) [33]. Oxidation yields the corresponding lactones. 

These reactions, performed many times, show, in addition to the reversal of the absolute configuration of the product with the change in the configuration at C-8 and C-9 of the alkaloids, a small but reproducible difference in the e.e. of the product. It is evident that the diastereomeric nature of quinine vs. quinidine and cinchonidine vs. cinchonine expresses itself via small but important energy differences in the best fits of the transition states. Noteworthy in this respect is the fine work of Kobayashi (20), who observed larger differences (in the e.e. s of products) when the diastereomeric cinchona alkaloids were used as catalysts after having been copolymerized with acrylonitrile (presumably via the vinyl side chain of the alkaloids). 

Metal ion chelates of various porphyrins, differing in their substituents at positions 1-8, are intimately involved in a great number of life processes. Iron protoporphyrin (13) is the most common form and serves as the cofactor of a large number of enzymes. Usually (13) is non-covalently bound to its conjugate apoenzymes. Examples of covalently attached (13) are provided by c-type cytochromes, the attachment being between two vinyl side chains of (13) and two cysteine residues of the protein. Other biologically important derivatives of porphyrin include chlorophyll a (14), bacteriochlorophyll a and heme a (B-79MI11002). 

Attempted Vilsmeier formylations (POCl3/DMF) of metalloporphyrins bearing vinyl side chains results in formylation of the vinyl group (to give 84) at a rate which is faster than methine formylation as a result, vinyl groups usually need to be protected as the 2-hydroxyethyl derivative (78) which, in one step, can be formylated and transformed into 2-chloroethyl (ready for dehydrochlorination to regenerate the vinyl) by treatment with thionyl chloride. 

A stereocontrolled Staudinger cycloaddition reaction has been reported to be performed on vinylketenes, possessing a y-heteroatom, and imines to produce frans-vinyl-(3-lactams [112]. The vinyl side chain adopted stereoselectively the (Z) configuration in the transition state, stabilizing the vinyl ketene and leading, exclusively, to the frans-3-vinyl-(3-lactam (Scheme 37). 

The siloxane polymer usually has a rather high molecular weight, and may have reactive ends for end-linking curing or vinyl side chains for peroxide curing. 

Aliphatic or aromatic peroxide curing agents can also be used, by reactions with vinyl side chains or even saturated alkyl groups. Specihc peroxides are chosen on the basis of their decomposition temperatures, and the reaction products they leave behind after the curing process is complete. Some peroxides used are Mv(2,4-dichloroben-zoybperoxide, benzoyl peroxide, dicumyl peroxide, and di-t-butyl peroxide.83-86... 

Static H 2D NOE spectroscopy was applied in a first experiment showing that the technique can be used to measure inter-chain interactions [44], This work was then continued by applying the technique under MAS to investigate the inter-molecular interactions responsible for the miscibility in polybutadiene/polyisoprene blends above the Tg [45]. It was shown that intermolecular association can be probed by this technique and the results reveal the existence of weak intermolecular interactions between the polyisoprene methyl group and the vinyl side chain of the polybutadiene. 

Influence of the presence of a vinyl side chain (heliannuol C) versus an isopropyl side chain (heliannuol B) in the germination of onion. 

Through sulfur ylide reactions rings can be enlarged by three atoms, two from the vinyl side chain and a third one from the a-alkyl substituent of the sul-fonium ion. The reaction product is, like the starting material, a thiacycloalkane... 

Va represented one stereochemically satisfactory example of the possibilities (71). The reaction of gelsemine with diethyl azodicarboxylate rendered the first of these untenable, but the structure VI (position of ether link again unspecified), advanced in lieu of Va or Vb (75) was in turn invalidated by the discovery that the molecule contains a vinyl side chain. 

Most known multiheme cytochromes and enzymes belong to the family of cytochromes c (see Iron Heme Proteins Electron Transport), which contain Fe-protoporphyrin IX covalently attached to the polypeptide chain by two thioether bonds, formed by addition of two cysteinyl residues to the vinyl side-chains of the porphyrin ring. The two cysteines form a characteristic amino acid sequence motif CXXCH, usually indicative of heme c ligation, and where the histidine is the axial fifth ligand to the iron. For some cytochromes (see Section 2), the number of residues between the two cysteines can be three or four. The heme redox potentials in cytochromes c cover a wide range and are tuned by several factors, usually dominated by the type of axial ligation and the extent of solvent exposure of the heme. ... 

Direct attack of the monomer on the metal is a heterogeneous reaetion. The lithium was used as a fine dispersion with a large surface area to speed up the initiation reaction, and the process was carried out in hydrocarbon solvents because polar solvents increase the generally undesired vinyl side chain content of the product polymer (cf. Section 9.2.7). 

Recently Gajewski and Warner have reportedan experiment designed to circumvent the mechanistic complication caused by the intermediacy of transoid biradicals in the thermal reactions of vinylcyclopropanes. They reasoned that attachment of a r-butyl group to the vinyl side chain, as shown in Figure 25, would sterically disfavor the conformation of the reactant that would tend to give a transoid biradical. Apparently this strategy was successful because they found a diene cyclopentene ratio of 2.38 1 (for the unlabeled compound at 280.0° C) instead of the more normal 11-16 1. 

When the diene is incorporated, some methyl groups will be replaced by vinyl side chains. These can be cross-linked with sulfur in the manner of rubber. Rubber is, of course, polyisoprene. 

UnsaCuraCed Aromatic Compounds. Although they do not ordinarily do so in free-radical polymerization, aromatic compounds with allyl or vinyl side chains should be capable, under certain conditions, of undergoing reaction not only in the side chains but also at the ring. This has... 

Tetrafunctlonal monomers or polymers with vinyl side chains offer the unique possibility of quantum amplification by spatial polymerization. This reaction Is also shown In Figure 6. Multlcentered polymerization by chain reaction provides high speed and the mechanical-physical strength of a crossllnked polymer. However, because of the rapid Increase In viscosity, the amplification may not be as large as expected. 

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