Buta reaction + olefins

Free radical addition of HBr to buta-1,2-diene (lb) affords dibromides exo-6b, (E)-6b and (Z)-6b, which consistently originate from Br addition to the central allene carbon atom [37]. The fact that the internal olefins (E)-6b and (Z)-6b dominate among the reaction products points to a thermodynamic control of the termination step (see below). The geometry of the major product (Z)-(6b) has been correlated with that of the preferred structure of intermediate 7b. The latter, in turn, has been deduced from an investigation of the configurational stability of the (Z)-methylallyl radical (Z)-8, which isomerizes with a rate constant of kiso=102s 1 (-130 °C) to the less strained E-stereoisomer (fc)-8 (Scheme 11.4) [38]. 

In developing the mechanism, it was assumed that the adsorbed state of buta-1 2-diene active in hydrogenation was the di-7r-adsorbed species C in Fig. 32. The close similarity in the ZV-profiles for each butene formed in a given reaction suggests that each was formed as a primary product and the general mechanism shown in Fig. 33 was proposed. The difference in behaviour of the type A and B catalysts was explained by proposing that, at the type A surface, a-bonded and 7r-olefinic species are of importance as... 

Low-energy electron bombardment of monolayers of ethylene on a silver(lll) surface brings about C—H bond fission. The H is absorbed on the surface and the vinyl radical dimerizes to yield buta-1,3-diene. Higher doses of electrons lead to the formation of ethyne Olefins can undergo catalytic oxidation when they are irradiated in the presence of silver catalysts either as silver powder or supported silver metals on anatase titania, sihca and porous glass. Irradiation under these conditions increases the reaction rate. When the surface is coated with ethene and deuterium, partly deuteriated ethene is formed on irradiation, presumably as a result of a vinyl radical reacting with deuterium. UV... 

The interesting olefin perfluoromethylenecyclopropane (see p. 59) fails to undergo the familiar [2 + 2] additions of fluoro-olefins possibly for steric reasons, but it is a reactive dienophile in the Diels-Alder reaction. Cyclopentadienc yields adduct (106) at 0 °C buta-1,3-diene and fra s,fra/i,y-hcxa-2,4-diene (but not the CIS,CIS- or cis,trans-isomsrs) react at 100 °C anthracene gives the expected adduct at 100 °C and quadricyclane yields adduct (107) at 25 °C. The isomeric perfluoro-1-methylcyclopropene forms Diels-Alder adducts with cyclopentadiene and buta-1,3-diene with equal facility. ... 

The Diels—Alder reaction involves the addition of a dienophile, which is an olefinic or acetylinic compound, to the 1,4-position of a conjugated diene system to produce a cyclohexene. Since the reaction forms a cyclic product, via a cyclic transition state by the addition of a 47T-electron system (i.e., diene) to a 27t-electron system (i.e., dienophile), it can also be described as a [7t" s -I- TT s] cycloaddition reaction. Numbers 4 and 2 identify both the number of TT-electrons involved in the electronic rearrangement and the number of atoms in the cyclohexene ring. The letter s indicates that the reaction takes place suprafacially on both the components. The reaction between buta-1,3-diene and ethene to give cyclohexene is a typical example of Diels—Alder reaction (Scheme 4.5). 

Homologation of olefins by four carbon atoms is achieved by reaction of the derived borane (265) with buta-1,3-diene monoxide in the presence of catalytic amounts of oxygen. Trialkylboranes are also converted into the 4,4-dialkyl-c/j-but-2-ene-l,4-diols (266) in good yields by addition to a-lithiofuran and oxidation of the intermediate boroxarocyclohexenes (267) with hydrogen peroxide. ... 

Upon irradiation of hexa-terf-hutyl-cyclotrisilane in the presence of olefins such as cyclopentane, cyclohexane, styrene, or allylhenzene the corresponding siliranes are formed in good to excellent yields. The colorless liquids can be separated from the less-volatile reaction products of the disilene via distillation under reduced pressure (4). Interestingly, conjugated olefins such as 2,3-dimethyl-buta-l,3-diene, isoprene, 2,3-dimethoxy-buta-l, 3-diene, cyclohexa-1,3-diene, or cyclopenta-1,3-diene, reacted not yield the expected five-membered rings but the corresponding vinyl-siliranes (4). The nonconjugated alkene norbomadiene also reacts selectively to the endo-silirane (4). 

Zirconium dioxide shows specific catalytic actions for the cleavage of a C-H bond (ref.8) and the hydrogenation of buta-1,3-diene by a molecular hydrogen and hydrogen donor molecules such as cyclohexadiene (refs.9-11) and high selectivities for the formation of 1-olefins from secondary alcohols (ref.12) and of isobutane in CO + H2 reaction (ref.l3). Recently decomposition of triethylamine to yield acetonitrile, in which both dealkylation by acidic sites and dehydrogenation by basic sites were involved, was reported (ref.14). These characteristic behaviors of Zr02 are considered due to the acid-base... 

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