Dimerization olefin

Other Dimer Olefins. Olefins for plasticizer alcohols are also produced by the dimerization of isobutene [115-11-7] 4 8 codimerization of isobutene and / -butene [25167-67-3]. These highly branched octenes lead to a highly branched isononyl alcohol [68526-84-1] product. BASE, Ruhrchemie, ICl, Nippon Oxocol, and others have used this source. 

A simple kinetic criterion is applicable in those a-eliminations which lead to the formation of dimeric olefins (see Fig. 2). In basic media, a number of organic halides and onium salts, characterized by the absence of a /J-hydrogen, undergo this reaction. It can be formulated as... 

A widely exploited procedure for bringing about carbenoid reactions of organic mono- and fifem-dihalides is by use of lithium alkyls. Examples are given in equations (11) and (12). Dimeric olefin formation, stereospecific cyclopropane formation from olefins, and insertion into carbon-hydrogen bonds have all been observed in suitable cases, together with further reactions of these products with excess of the lithium alkyl. 

Reaction with iam dihaUdes. Dicobalt octacarbonyl reacts at 50° with activated gem-dihalides in THF or benzene first to give a coupling product, which is then dehalogenated to the dimer olefin ... 

Dichlorodiphcnylmcthanc and 9,9-dibromofluorcne react in this way to give the dimer olefin in high yield. 

It was earlier discussed that 1,3-dithiolanes underwent an interesting desulfurdimerization reaction leading to dimeric olefins on treatment of metal carbonyls, such as W(CO)6 or MofCO) <1995JOC7380>. In the case of the monomeric 296, this reaction performed with W(CO)6 in refluxing chlorobenzene for 48-60 h afforded the corresponding oligophenylenevinylenes (OPVs) 297 in 67-81% yields (Equation 28) <2001JOM(1)63> . 

Completion of the monomeric unit was achieved via Swem oxidation and Arbuzov reaction with trimethylphosphite to give the phosphonate 75 in 31% overall yield from the resolved amino alcohol. Dimeric olefination was effected upon deprotonation to yield the macrocycle 76, which could be converted in 81% yield to optically active vermiculine (56) via sequential cleavage of the thioketal and ketal protecting groups. 

Moreover, ESR studies show that when the temperature of the sample is raised, trapped radicals recombine just below a transition point or below the melting point (2, 13, 15, 16). When the melting point of the irradiated hydrocarbon is low, the only fate for a trapped radical is recombination with another radical. Indeed, at low temperature, the rate constants of the other reactions are very small. After melting, trapped radicals will be found as dimers, olefins, or parent molecules. This work completes the ESR study of the radiolysis of solid hydrocarbons at low temperature and reports the first results on the radiolysis of n-pentane. We studied only heavy and unsaturated products. 

Unlike all the other substituted 9-bromofluorenes, the highly acidic 3-nitro-9-bromo isomer is converted extensively into its conjugate base by bases in /-butyl alcohol . The rate of elimination can thus be followed by monitoring the absorption of the blue carbanion rather than the red olefinic product, as is otherwise employed. Extensive carbanion formation is also observed with 4-nitrobenzyl chloride and 4-nitrodiphenylmethyl chloride. For all three of these substrates, the rate of elimination shows a complex dependence on the substrate concentration, but an inverse dependence on the medium basicity. This observation is not consistent with a carbene mechanism but accords with the displacement scheme if the substrate is always more than half-ionised under the reaction conditions. To achieve a rapid successful preparative conversion to the dimeric olefin, it is necessary to keep the substrate in an excess of the base in order to maximise the concentration of unionised substrate on which the carbanion can exert a displacement. 

A number of benzylic halides and onium salts under the influence of base undergo an apparent a-elimination to yield dimeric olefins, viz. 

Metal carbonyl complexes readily displace halogen atoms of organic halides, producing reactive species which are useful in organic synthesis. Certain ge/w-dihalides are reduced with iron pentacarbonyl (Coffey, 1961) or dicobalt octacarbonyl (Seyferth and Millar, 1972) or molybdenum hexa-carbonyl (Alper and Des Roches, 1976) to form dimeric olefin products. Ordinary monohalides are much less reactive, however. 

---