Telomerization reaction

A simple template-free methyl acrylate telomerization was conducted using the cyclohexyl iodide/allyltributyltin system in order to identify retention times for the telomers 26 from the ACT reactions. Telomerization of methyl acrylate (900 mM) with 120 mM cyclohexyl iodide and 300 mM allyltributyltin gave 27% of the n=4 telomers. Scheme 8-10. Under the best GC conditions found, only four different n=4 telomers, out of a possible 16, were observed in this product mixture. This experiment gives a baseline value for telomer distribution obtained without the use of a template. It is clear that simple template-free telomerization is not useful for the preparation of an oligomer of a specific length. 

As result of such a reaction telomere molecules are formed, which differ from the oligomer molecules by their ends. These are laige substituents coming from the decomposition of the solvent molecule (e.g., Cl and such groups as CCI3, CHCl, CH CH Cl, etc.), which exert a decisive influence on the properties of the final product. For this reason, telomeres cannot be equated with oligomers, which do not have reactive terminal functional groups. 

Dimerization and Telomerization of Conjugated Dienes and Related Reactions... 

The dimerization of isoprene is possible, but the reaction of isoprene is slower than that of butadiene. Dimerization or telomerization of isoprene, if carried out regioselectively to give a tail-to-liead dimer 18 or a head-to-tail... 

Although acetonitrile is one of the more stable nitriles, it undergoes typical nitrile reactions and is used to produce many types of nitrogen-containing compounds, eg, amides (15), amines (16,17) higher molecular weight mono- and dinitriles (18,19) halogenated nitriles (20) ketones (21) isocyanates (22) heterocycles, eg, pyridines (23), and imidazolines (24). It can be trimerized to. f-trimethyltriazine (25) and has been telomerized with ethylene (26) and copolymerized with a-epoxides (27). 

A telomerization reaction of isoprene can be carried out by treatment with 2-chloro-3-pentene, prepared by the addition of dry HCl to 1,3-pentadiene (67). An equimolar amount of isoprene in dichi oromethane reacts with the 2-chloro-3-pentene at 10°C with stannic chloride as catalyst. l-Chloro-3,5-dimethyl-2,6-octadiene is obtained in 80% yield by 1,4-addition. 

Synthetic methods for the production of citroneUal iaclude the catalytic dehydrogenation of citroneUol (110), the telomerization of isoprene (151), and the Utbium-catalyzed reaction of myrcene with secondary alkylamines (128). 

Telomerization Reactions. Butadiene can react readily with a number of chain-transfer agents to undergo telomerization reactions. The more often studied reagents are carbon dioxide (167—178), water (179—181), ammonia (182), alcohols (183—185), amines (186), acetic acid (187), water and CO2 (188), ammonia and CO2 (189), epoxide and CO2 (190), mercaptans (191), and other systems (171). These reactions have been widely studied and used in making unsaturated lactones, alcohols, amines, ethers, esters, and many other compounds. 

Coupling of butadiene with CO2 under electrochemically reducing conditions produces decadienedioic acid, and pentenoic acid, as weU as hexenedioic acid (192). A review article on diene telomerization reactions catalyzed by transition metal catalysts has been pubUshed (193). 

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). 

Homolytic cleavage of dlazonlum salts to produce aryl radicals is induced by titan1um(III) salt, which is also effective in reducing the a-carbonylalkyl radical adduct to olefins, telotnerization of methyl vinyl ketone, and dimerization of the adduct radicals. The reaction can be used with other electron-deficient olefins, but telomerization or dimerization are important side reactions. 

Chloro-2,2,3-trifluoropropionic acid has been prepared by permanganate oxidation of 3-chloro-2,2,3-trifluoropropanol which is one of the telomerization products of chlorotrifluoroethylene with methanol. The present procedure is a modification of one reported earlier and is undoubtedly the method of choice for making propionic acids containing 2 fluorine atoms, i.e., 2,2,3,3-tetrafluoropropionic acid, 3,3-dichloro-2,2-difluoropropionic acid, and 3-bromo-2,2,3-trifluoropropionic acid. When preparing 2,2,3,3-tetrafluoropropionic acid from tetrafluoroethylene, it is desirable to use an additional 50 ml. of acetonitrile and externally applied heat to initiate the reaction. 

Similarly, Itexafluoroprapylene undergoes fluoride ion induced homotelo-merization to give a series of dimers and trimers These telomerizations can be induced by other nucleophiles, such as amines Indeed, the selectivity of the pi oce-,s can be changed significantly by varying reagents and reaction conditions [25, 26] (equations 19 and 20)... 

In addition to the applications reported in detail above, a number of other transition metal-catalyzed reactions in ionic liquids have been carried out with some success in recent years, illustrating the broad versatility of the methodology. Butadiene telomerization [34], olefin metathesis [110], carbonylation [111], allylic alkylation [112] and substitution [113], and Trost-Tsuji-coupling [114] are other examples of high value for synthetic chemists. 

When the products are partially or totally miscible in the ionic phase, separation is much more complicated (Table 5.3-2, cases c-e). One advantageous option can be to perform the reaction in one single phase, thus avoiding diffusional limitation, and to separate the products in a further step by extraction. Such technology has already been demonstrated for aqueous biphasic systems. This is the case for the palladium-catalyzed telomerization of butadiene with water, developed by Kuraray, which uses a sulfolane/water mixture as the solvent [17]. The products are soluble in water, which is also the nucleophile. The high-boiling by-products are extracted with a solvent (such as hexane) that is immiscible in the polar phase. This method... 

Although sulfonyl chlorides add readily to unactivated olefins, with vinylic monomers telomeric and/or polymeric products were observed. This difficulty has been overcome by carrying out the addition in the presence of catalytic amounts of CuCl2, so as to provide a general and convenient synthesis of /5-chlorosulfones (Asscher-Vofsi reaction)63. For the copper-catalyzed system a redox-transfer mechanism has been suggested in which the... 

ORGANOBROMINE COMPOUNDS IN REACTIONS OF HOMOLYTIC ADDITION AND TELOMERIZATION... 

The first examples of stereo-controlled radical addition and telomerization reactions are discussed. 

The essential difference in chemical behavior of chlorides and bromides used as telogens (addends) can be distinctly seen when the reactions of chloro- and bromoacetates are compared. In addition and telomerization reactions monochloroacetates react with 1-alkenes exclusively at C-H bond [under initiation... 

The adducts containing di- and tribromomethyl groups can react with another molecule of monomer, i.e. the secondary reactions occur including step-by-step telomerization in this case. The presence of the bromine atom adjacent to the radical center makes it probable the fragmentation with ejection of the bromine atom, which starts the further reaction, and as a result, the products of bromine addition to a double bond, not adducts, are formed. 

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 ... 

One more example of the similar reaction is the addition of bromotrichloromethane to (S)-l-acryloyl-2-methoxycarbonylpirrolidine catalyzed with system [Fe(CO)5 + PPh3] (75°C) (ref, 18). In this case the authors managed to exclude telomerization virtually and obtain adduct in 80 % yield, which is one of two possible diastereomers. 

Dibromodichoromethane was studied as telogen in the reaction with vinyl chloride (ref. 7). The authors showed that the reaction occurred as telomerization (under usual conditions) the changes in monomer / telogen ratio (from 1.5 to 15) allowed to vary the adduct content from 80 to 30 %. 

The water-aleohol method provided more dispersed catalysts than the impregnation method. The case of copper, the Cu particles of about 20 nm showed enhanced stability and higher activity than the particles larger than 40 nm. In the effect of active metal, copper was better stable and aetive than silver and zinc. In case of telomerization reaction, the most suitable reaction temperature was 380 410°C. 

Nielsen DJ, Cavell KJ (2006) Pd-NHC complexes as catalysts in telomerization and aryl amination reactions. In Nolan SP (ed) N-Heterocyclic carbenes in synthesis. WUey-VCH, Weinheim, pp 73-102... 

In an analoguous case, two-phase telomerization of butadiene with ammonia to give octadienylamine has been reported where higher selectivity is realized in a two-phase system of water-toluene. Here, octadienylamine is more reactive than ammonia and consecutive reaction leads to sec and ten amines. By adopting a two-phase strategy, a primary amine selectivity as high as 91 % has been realized (Drieben-Hoscher and Keim, 1998). 

Scheme 5-4 Platinum-catalyzed hydrophosphination of acrylonitrile using PH3 (Eq. I) and PH (CH2CH2CN)2 (Eq. 2). The proposed structure of a telomeric by-product of this reaction (I) Is also shown...

Butadiene telomerization using nitroethane as a trapping reagent is applied to the total synthesis of the natural product, recifeiolide, where the secondary nitro group is converted into the ketogroup by the Nef reaction, and the terminal double bond is converted into the iodide via hydro alumination (Scheme 5.6).71... 

Extension to carbocyclization of butadiene telomerization using nitromethane as a trapping reagent is reported (Eq. 5.48).72 Palladium-catalyzed carbo-annulation of 1,3-dienes by aryl halides is also reported (Eq. 5.49).73 The nitro group is removed by radical denitration (see Section 7.2), or the nitroalkyl group is transformed into the carbonyl group via the Nef reaction (see Section 6.1). 

CO2 [67]. Early work examining the free-radical telomerization of TFE in supercritical C02 took advantage of the high solubility of the low molecular weight perfluoroalkyl iodides products to prepare these materials homogeneously [77]. In these reactions, we utilized perfluorobutyl iodide as the telogen... 

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