2,3-dimethyl-2-butene, addition

The dimerization of propene has been extensively studied because the propene dimers are of considerable interest as fuel additives and as starting materials for the preparation of monomers (4, 48, 49, 101). The reaction course can be controlled to give methylpentenes, 2,3-dimethyl-butenes (2, 4, 7, 47, 51), or hexenes (44-46) as the main products. 

One of the industrially important dimerization reactions that involves the use of homogeneous catalysts is the dimerization of propylene. Dimerization of propylene produces mixtures of the isomers of methyl pentenes, hexenes, and 2,3-dimethyl butene and is practiced by the Institut Francis du Petrole (IFP), Sumitomo, and British Petroleum (BP). The methyl pentenes and hexenes are used as gasoline additives. Dimethylbutene is used in the fragrance and the agrochemical industries. 

To explain this observation, experiments have shown that 2,3-dimethyl-butene reacts with ozone to give 140 by initial dipolar addition however, a rearrangement occurs to give 139, which is commonly called an ozonide. When 139 is treated with aqueous hydrogen peroxide in a second chemical step, two molar equivalents of acetone are formed. The overall transformation cleaved both bond of the C=C unit, converting each carbon to a carbonyl. The overall process is called oxidative cleavage and will be elaborated in Chapter 17, Section 17.4. 

In laser-impulse experiments with chlorophenyldiazirine the carbene could be observed by UV spectroscopy. On addition of defined amounts of alkene the rate of cyclopropanation was measured directly. The rate constants with various alkenes were (lO moF s ) 1-hexene, 1.3 ( )-2-pentene, 34 2-methyl-2-butene, 77 2,3-dimethyl-2-butene, 130 (80JA7576>. 

The photolysis of a-diazosulfones dissolved in alkenes provides sulfonyl-substituted cyclopropanes in high yields. This is exemplified by the preparation of l-(p-methoxyphenylsulfonyl)-2,2,3,3-tetra-methylcyclopropane in 75% yield from -methoxybenzenesulfonyl-diazomethane and 2,3-dimethyl-2-butene. A similar addition to [Pg.101]

An alternative view of these addition reactions is that the rate-determining step is halide-assisted proton transfer, followed by capture of the carbocation, with or without rearrangement Bromide ion accelerates addition of HBr to 1-, 2-, and 4-octene in 20% trifluoroacetic acid in CH2CI2. In the same system, 3,3-dimethyl-1-butene shows substantial rearrangement Even 1- and 2-octene show some evidence of rearrangement, as detected by hydride shifts. These results can all be accoimted for by a halide-assisted protonation. The key intermediate in this mechanism is an ion sandwich. An estimation of the fate of the 2-octyl cation under these conditions has been made ... 

Addition of hydrogen chloride to 3,3-dimethyl-1-butene gives a... 

Intramolecular oxonium ylide formation is assumed to initialize the copper-catalyzed transformation of a, (3-epoxy diazomethyl ketones 341 to olefins 342 in the presence of an alcohol 333 . The reaction may be described as an intramolecular oxygen transfer from the epoxide ring to the carbenoid carbon atom, yielding a p,y-unsaturated a-ketoaldehyde which is then acetalized. A detailed reaction mechanism has been proposed. In some cases, the oxonium-ylide pathway gives rise to additional products when the reaction is catalyzed by copper powder. If, on the other hand, diazoketones of type 341 are heated in the presence of olefins (e.g. styrene, cyclohexene, cyclopen-tene, but not isopropenyl acetate or 2,3-dimethyl-2-butene) and palladium(II) acetate, intermolecular cyclopropanation rather than oxonium ylide derived chemistry takes place 334 ). 

Dimethyl-4-silacyclohexadienylidene (lv) is of interest as a potential source of silaxylene 24, however, all attempts to convert the carbene into an aromatic compound failed.107 The only isolated product from gas phase reactions is the dimer 25. In solution, carbene lv was found to add stereospecifically to cis-2-butene. With butadiene as trapping reagent both the products of the 1,2- and 1,4-addition 26 and 27, respectively, are observed (Scheme 21).107 In addition, silacyclopentene 28 is formed, which is the trapping product of cyclo-... 

Ceric ammonium nitrate promoted oxidative addition of silyl enol ethers to 1,3-butadiene affords 1 1 mixtures of 4-(/J-oxoalkyl)-substituted 3-nitroxy-l-butene and l-nitroxy-2-butene27. Palladium(0)-catalyzed alkylation of the nitroxy isomeric mixture takes place through a common ij3 palladium complex which undergoes nucleophilic attack almost exclusively at the less substituted allylic carbon. Thus, oxidative addition of the silyl enol ether of 1-indanone to 1,3-butadiene followed by palladium-catalyzed substitution with sodium dimethyl malonate afforded 42% of a 19 1 mixture of methyl ( )-2-(methoxycarbonyl)-6-(l-oxo-2-indanyl)-4-hexenoate (5) and methyl 2-(methoxycarbonyl)-4-(l-oxo-2-indanyl)-3-vinylbutanoate (6), respectively (equation 12). 

The cycloaddition of A-benzoyliminochloromethanesulfenyl chloride and 3,3-dimethyl-2-butene in nitromethane and in the presence of lithium perchlorate involves addition of the electrophile at the double bond and 1,2-methyl shift. Unusually, the ring closure is accompanied by elimination of the benzoyl group (Equation 16) <2002CHE1150>. 

Figure 6.8 summarizes the mechanism of the reaction of N03 with 2,3-dimethyl-2-butene (Skov et al., 1994 Olzmann et al., 1994). The addition of the NO-, to a double bond is about 20 kcal mol-1 exothermic, so that the initially formed adduct is excited and either can be stabilized or decompose by breaking the weaker C0-N02 bond to form the epoxide and N02. The stabilized adduct can also decompose in a similar manner, in competition with its reaction with 02. Under... 

FIGURE 6.9 Expected atmospheric fates of peroxy radical formed in N03 addition to 2,3-dimethyl-2-butene. 

Little evidence is available to determine whether aromatic ketones can act as singlet sensitizers. If they can do so, it will be only at high acceptor concentrations because the lifetime of benzophenone singlets,154 for example, is less than 2 x 10-10 sec and that of several other aromatic ketones is estimated to be less than 10 10 sec.155 Yang231 has noticed that the photochemical addition of benzophenone to 2,3-dimethyl-2-butene is less efficient in neat olefin than in 4M olefin, which may indicate deactivation of benzophenone singlets. Golub218 has mentioned that benzophenone is a singlet sensitizer in the photolysis of 1,4-dichlorobutane. 

Work of Yang242 and of Warwick and Wells243 has shown that two excited states are involved in the photochemical addition of 9-anthraldehyde (56) to 2,3-dimethyl-2-butene. Quenching by di-/-butylnitroxide gave a curved Stern-Volmer plot that could be analyzed to yield lifetimes of 1.0 and... 

This procedure describes the preparation of 3-nitropropanai, 1, employing the rarely encountered 1,4-addition of ambident nitrite ion with its "softer N-atom,2 and further transformations of 1, as reported earlier.3 A similar preparation of 3-nitrobutanal from crotonaldehyde (3-butenal) is known,4 as well as analogous additions to a, 3-enones.2 The reduction of 1 to the alcohol 2, originally carried out with borane-dimethyl sulfide (BMS),3 is now more conveniently and economically done with sodium borohydride. The acetalization of 1 to yield the dimethyl acetal 3 is based on our earlier report.3... 

Another simple oligomerization is the dimerization of propylene. Because of the formation of a relatively less stable branched alkylaluminum intermediate, displacement reaction is more efficient than in the case of ethylene, resulting in almost exclusive formation of dimers. All possible C6 alkene isomers are formed with 2-methyl-1-pentene as the main product and only minor amounts of hexenes. Dimerization at lower temperature can be achieved with a number of transition-metal complexes, although selectivity to 2-methyl-1-pentene is lower. Nickel complexes, for example, when applied with aluminum alkyls and a Lewis acid (usually EtAlCl2), form catalysts that are active at slightly above room temperature. Selectivity can be affected by catalyst composition addition of phosphine ligands brings about an increase in the yield of 2,3-dimethylbutenes (mainly 2,3-dimethyl-1-butene). 

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