Telomerization,Telomer

Telomerization. Polymerization of DAP is accelerated by telogens such as CBr, which are more effective chain-transfer agents than the monomer itself (65) gelation is delayed. The telomers are more readily cured in uv than DAP prepolymers. In telomerizations with CCl with peroxide initiator, at a DAP/CCl ratio of 20, the polymer recovered at low conversion has a DP of 12 (66). 

Carbon tetrachloride forms telomers with ethylene and certain other olefins (14—16). The mixture of Hquid products derived from ethylene telomerization may be represented CCl2(CH2CH2) Cl ia which nis 2l small number. Reaction of ethylene and carbon tetrachloride takes place under pressure and is induced by the presence of a peroxygen compound, eg, ben2oyl peroxide (17—19) or metal carbonyls (14,15). 

The authors (ref. 19) managed to perform this reaction selectively as telomerization at the C-Br bond of bromoform using initiating system Fe(CO)5 + DMF, which facilitates a bromine transfer at a step of a chain transfer (ref. 19). In this case only one row of telomers is formed which contain three bromine atoms in molecules ... 

These telomerization reactions of butadiene with nucleophiles are also catalyzed by nickel complexes. For example, amines (18-23), active methylene compounds (23, 24), alcohols (25, 26), and phenol (27) react with butadiene. However, the selectivity and catalytic activity of nickel catalysts are lower than those of palladium catalysts. In addition, a mixture of monomeric and dimeric telomers is usually formed with nickel catalysts ... 

The most characteristic reaction of butadiene catalyzed by palladium catalysts is the dimerization with incorporation of various nucleophiles [Eq. (11)]. The main product of this telomerization reaction is the 8-substituted 1,6-octadiene, 17. Also, 3-substituted 1,7-octadiene, 18, is formed as a minor product. So far, the following nucleophiles are known to react with butadiene to form corresponding telomers water, carboxylic acids, primary and secondary alcohols, phenols, ammonia, primary and secondary amines, enamines, active methylene compounds activated by two electron-attracting groups, and nitroalkanes. Some of these nucleophiles are known to react oxidatively with simple olefins in the presence of Pd2+ salts. Carbon monoxide and hydrosilanes also take part in the telomerization. The telomerization reactions are surveyed based on the classification by the nucleophiles. 

Telomerization of various primary and secondary alcohols has been carried out (45). The results obtained by using Pd(acac)2 and PPh3 at 60°C for 6 hours are shown in Table III. It can be said that primary alcohols react most easily with butadiene, but the higher the alcohol, the lower the reactivity to give the telomers. The reactivity of the secondary al-... 

Hydrosilanes react with butadiene by the catalysis of palladium compounds, but the nature of the reaction is somewhat different from that of the telomerization of other nucleophiles described before. Different products are obtained depending on both the structure of silanes and the reaction conditions. Trimethylsilane and other trialkylsilanes reacted with butadiene to give the 1 2 adduct, l-trialkylsilyl-2,6-octadienes (65), in high yield (98%) (62-64). Unlike other telomers which have the 1,6-octadienyl chain, the telomers of silanes have the 2,6-octadienyl chain. As catalysts, Pd(PPh3)2 (maleic anhydride), PdCl2(PhCN)2, PdCl2, and 7r-allylpalladium chloride were used. Methyldiethoxysilane behaved similarly to give the 1 2 adduct. 

The results in Table VI were obtained by the reactions at 80°C with Pd(acac)2 using different ligands in a mixture of methanol and isopropyl alcohol. From these results, it seems likely that reaction temperature has large influence on the regiospecificity of the telomerization. As another example, a mixture of isomeric telomers was obtained by the reaction of methanol and isoprene at 100° (95). 

Interestingly, the (co)telomers used behave as further potential telogens for subsequent telomerizations, and all of them can be end-capped with ethylene (E). 

Telnic bronze, 24 426 Telo-inertinite, 6 707t Telomeres, 17 610, 2 814 Telomer formation, 11 865 Telomerization, 2 261 butadiene, 4 374-375 TEMoo mode, 14 683. See also Gaussian mode (TEMoo)... 

At last, nucleolin might play a specific role in telomeric replication and maintenance, as suggested by two types of data. First, it binds telomeric repeat (TTAGGG)n in vitro (Ishikawa et al, 1993 Pollice et al, 2000), with a marked preference for the single-stranded form. Secondly, it interacts in vitro and in vivo with hTERT (Khurts et al, 2004), the protein catalytic component of human telom-erase. This interaction takes place both in the cytoplasm and in the nucleolus, where it could promote the assembly of hTERT with the RNA subunit hTERC. As a conclusion, many data regarding the involvement of nucleolin in DNA replication are indirect and an experimental demonstration through knockdown or knockout studies is still awaited. 

Note An oligomer obtained by telomerization is often termed a telomer. 

The telomerization of the lower reactive isoprene with glycerol was achieved in the presence of palladium-carbene complex but in a dioxane/PEG solvent [15]. Under such conditions, both glycerol and PEG are converted. After 24 h, in the presence of 0.06% [Pd(acac)2/IMes.Cl] (1/1.5) at 90°C, the telomerization of isoprene with glycerol (glycerol/PEG/dioxane/isoprene = 1/2.5/2.5/5) yields 70% of the linear monoether glycerol together with 29% of PEG telomer. 

To circumvent the formation of ditelomers and to attempt recycling of the catalysts, the telomerization of polyols was studied in the presence of water using water soluble catalysts such as Pd/TPPTS (TPPTS = tris(m-sulfonato-phenyl) phosphine trisodium salt) [9, 12, 16, 17]. Behr et al. studied the telomerization of ethylene glycol under biphasic conditions. Under such reaction conditions, 80% of mono-telomer are formed and only traces of ditelomer and butadiene dimers are detected (Fig. 4). This is attributed to the solubility of the monomer in the catalyst phase. However, the catalyst is unstable and decomposes rapidly, leading to almost inactive catalyst after three runs. This is due to TPPTS oxidation during the work-up of the reaction and can be avoided by addition of 2.5 equiv. ligand in the solution prior to each run. 

Fig. 22 Surface tension of a crude telomer mixture issued from the telomerization of 1 with bran syrup as a function of concentration...

Ar-Acrylamidohexanoyl -lactosylamine 51 was telomerized (AIBN, MeOH) in the presence of either tcrt-butylmercaptan or methyl mercapto-propionate to provide families of discrete telomers 52 and 53 separable by size-exclusion chromatography (Scheme 9) [74,75]. Using 5.5 equivalents of t-BuSH per monomer gave monoadduct (27%), dimer (14%), trimer (1%), and higher telomers 52 (45%) in 87% yield. When methyl mercaptopropionate was used (0.43 eq), monoadduct 54 (26%), dimer (22%), trimer (12%), tetramer (7%), and hi er telomers 53 (n > 5,31 %) were obtained. 

Although various transition-metal complexes have reportedly been active catalysts for the migration of inner double bonds to terminal ones in functionalized allylic systems (Eq. 3.2) [5], prochiral allylic compounds with a multisubstituted olefin (Rl, R2 H in eq 2) are not always susceptible to catalysis or they show only a low reactivity [Id]. Choosing allylamines 1 and 2 as the substrates for enantioselective isomerization has its merits (1) optically pure citronellal, which is an important starting material for optically active terpenoids such as (-)-menthol, cannot be obtained directly from natural sources [6], and (2) both ( )-allylamine 1 and (Z)-allylamine 2 can be prepared in reasonable yields from myrcene or isoprene, respectively, The ( )-allylamine 1 is obtained from the reaction of myrcene and diethylamine in the presence of lithium diethylamide under Ar in an almost quantitative yield (Eq. 3.3) [7], The (Z)-allylamine 2 can also be prepared with high selectivity (-90%) by Li-catalyzed telomerization of isoprene using diethylamine as a telomer (Eq. 3.4) [8], Thus, natural or petroleum resources can be selected. 

Photolysis of this polymer gives radicals on which side chains can be formed, giving graft polymerization 122, 123, 153). Similarly the polymerization of styrene (152) or vinyl acetate (157) in the presence of bromotrichloromethane gives telomers carrying terminal bromine atoms and trichloromethyl groups. By ultraviolet irradiation (3500 A) in the presence of methyl methacrylate the carbon-bromine links are broken and block copolymers are formed. The telomerization of acrylonitrile and acrylic acid with bromoform is based on the same technique the end groups of both polyacrylonitrile and polyacrylic acid were photolyzed in the presence of acrylamide and afforded polyacrylamide blocks linked to polyacrylonitrile or polyacrylic acid blocks (164, 165). 

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