M-But-2-ene

The addition to alkenes of radicals derived from an a-nitroketone is also catalysed by manganese(III) [30]. During the reaction between a-nitroacetophenone 8 and m-but-2-ene, the stereochemical relationship between the methyl substituents is not preserved. The process terminates with the formation of a nitrone. A related process will generate nitromethyl radicals from nitromethane and these add to benzene to give phenyinitromethane [31],... 

Meta photocycloaddition was discovered simultaneously and independently by two groups in 1966. Wilzbach and Kaplan [4] found that the adducts from m-but-2-ene, cyclopentene, and 2,3-dimethylbut-2-ene with benzene are substituted tricyclo 3.3.0.02X]oct-3-enes. The adducts were formed by irradiation of solutions (-10%) of the olefins in benzene, at room temperature under nitrogen, with 2537-A light. Bryce-Smith et al. [5] subjected an equimolar mixture of m-cyclooctene at room temperature or in the solid phase at 60°C to ultraviolet radiation of wavelength 235-285 nm. A mixture of 1 1 adducts was obtained from which the main component (-85%) was readily obtained pure by treatment of the mixture with methanolic mercuric acetate. This 1 1 adduct proved to be a meta photocycloadduct (Scheme 2). The minor nonaromatic adduct (10-15%) could, at that time, not yet be obtained completely free from the meta photocycloadduct the structure of a rearranged ortho adduct was provisionally assigned to this isomer. 

Most physical properties of alkenes are similar to those of the corresponding alkanes. For example, the boiling points of but-l-ene, m-but-2-ene, fran.v-but-2-ene, and n-butane... 

The electrophile does not need to be a proton. Bromine adds to double bonds to give the 1,2-dibromo compound (reaction 5.21). The intermediate bromonium cation here is believed to have the cyclic structure 27 rather than the open structure 28 because of the stereochemistry of the products, trans-But-2-ene (29) reacts with bromine to give the optically inactive meso dibromide 31 as a single compound (reaction 5.22) [m-but-2-ene gives an equimolar mixture of the two enantiomers (R,R)- and (S,S)-2,3-dibromobutane, which is also optically inactive]. 

N-acyl group with the consequence that the sulphinamide N—S bond is easily attacked by various nucleophiles. In the case of 2-alkyl(or aryl)sul-phonylthiazines it has been shown that the ring-opening process with the nucleophiles HO, RO, or RS results in the formation of derivatives of 4-sulphonylamino-m-but-2-ene sulphinates [e.g. (4) -> (5)], whereas with... 

The formation of /ra/M-but-2-ene and cw-but-2-ene is interpreted in terms of the reduction of two cyanonickel intermediates oti and oc which contain a TT-methylallyl and a w-buta-l,3-diene ligand respectively, the i species yielding predominantly the traw -isomer whereas 2 gives the ciy-form. 

J as-Dimethyl. b (Z)-But-2-ene gave the m-dimethyl product ( )-but-2-cnc gave the /ram-dimethyl product. c (Z)-Hex-3-ene gave the cw-diethyl product (A )-hex-3-cnc gave the frans-diethyl product. d Product 2,2-dichloro-3- or -4-trimethylsilylcyclobutanonc. 

The concerted nature of these reactions is also supported by the pyrolytic cleavage of cis-2,3-dimethylcyclobutanone and rra i-2,3-dimethylcyclobutanone at a temperature of 325 °C under a pressure of 10 Torr, from which approximately 99% retention of configuration in the resulting but-2-enes is observed.92,93 Moreover, the results obtained from the thermolysis of cis- and m -2,4-dimethylcyclobutanone also lend support to the concertedness of this reaction.92,93 However, as substantiated by Arrhenius parameters, a diradical pathway is the most likely competing reaction in the pyrolysis of 2-chlorocyclobutanone.94 On the other hand, the kinetics of the gas-phase pyrolysis of bicyclo[3.2.0]hept-2-en-6-one (14),95 bicyclo[3.2.0]heptan-6-one (IS)96 and 2,2-dimethyl-3-ethoxycyclobutanone (16)97 are commensurate with a concerted cycloreversion mechanism involving four-center auasi-zwitterionic transition structures. 

Favorable sorption sites for the butene isomers were found to be the double 10-rings of the three-dimensional channel system. Thus, diffusion was investigated between adjacent 10-rings. Results showed that the diffusion was an activated process the lowest barrier was 17.5 kJ/mol (but-l-ene) and the largest 22.5 kJ/mol (m-but-2-enc). The authors concluded that all of the three-dimensional channel system is accessible by the four butene isomers, since the diffusion barriers are small enough to be overcome at ambient temperatures. 

In the presence of 12, allyl methyl sulphide undergoes self-metathesis leading to MeSCH2CH=CHCH2SMe (90% trans), and cometathesis with cw-but-2-ene leading to MeCH=CHCH2SMe (75% trans)m. 

Z)-But-2-ene-l,4-diol.24 But-2-yne-l,4-diol (20g) is dissolved in methanol (350ml) and hydrogenated at atmospheric pressure in the presence of 0.5 per cent palladium-on-calcium-carbonate (2.0 g). After 24 hours one equivalent of hydrogen (5650 ml) will be absorbed. The catalyst is then separated and the filtrate distilled, giving (Z)-but-2-ene-l,4-diol as a colourless oil (15.7g, 77%), b.p. 134-135 °C/15 mmHg, n 5 1.4716. The product forms a dibenzoate (prisms from aqueous methanol), m.p. 69-70 °C. 

To a stirred suspension of diisopinocampheylborane (50 mmol) (1) in tetra-hydrofuran (18 ml) is added 4.5 ml of (Z)-but-2-ene. The reaction mixture is stirred at 25 °C for 4.5 hours. The solid diisopinocampheylborane disappears and the formation of the trialkylborane is complete. The organoborane is treated with 4 ml of methanol, followed by 18.3 ml of 3 m sodium hydroxide and the careful addition of 20 ml of 30 per cent hydrogen peroxide, maintaining the temperature of the reaction below 40 °C. The reaction mixture is further stirred at 55 °C for 1 hour, cooled, and extracted with ether (3 x 50 ml). The extract is washed successively with water (2 x 25 ml) and brine (3 ml) and dried over magnesium sulphate. The organic layer is carefully fractionated to provide butan-2-ol, b.p. 96-98 °C, 2.9 g (73%), purity > 95 per cent. The last traces of impurities are removed by preparative g.l.c. (2) to yield (R)-butan-2-ol, [a] 3 —13.23° (neat), ee 98.1 per cent. 

As mentioned in the above sub-section ( Adsorbed Species ), physisorbed, i,e., weakly bound, species can generally be observed with conventional liquid-state spectrometers. It is important to realise, therefore, that many catalytic reactions which occur via fairly loosely bound species can be perfectly adequately followed by such n.m.r. techniques. The isomerization of alkenes has been reported recently by Nagy etal for but-l-ene to cis- and tnz/is-but-2-ene over mixed Sn-Sb oxide catalysts145 and earlier over zeolites.146 A mechanism has been proposed involving a cyclic intermediate. When the catalyst is NiO/Si02, however, dimerization occurs,147 which in the case of propene leads to a mixture of isomers of hexene, the composition of the mixture depending upon the reaction temperature. 13C-enriched propene was used in this study. 

Compounds with permanent dipole moments engage in dipole-dipole attractions, while those without permanent dipole moments engage only in van der Waals attractions. cw-But-2-ene and fran -but-2-ene have similar van der Waals attractions, but only the cis isomer has dipole-dipole attractions. Because of its increased intermolecular attractions, m-bul-2-ene must be heated to a slightly higher temperature (4 °C versus 1 °C) before it begins to boil. 

In Fig. 7.1, the metal hydride 7.1 is the important catalytic intermediate. Conversion of 7.2 to 7.3 involves insertion of 1-butene in the M-H bond in a Markovnikov manner. Complex 7.4 is the anti-Markovnikov product. But-2-ene is formed from the Markovnikov product by /8-hydride elimination. A slightly different mechanism involves 1,3-hydrogen shift and the involvement of a Tj3-allyl rather than a metal-alkyl intermediate. This is shown schematically in Fig. 7.2. 

Musilek, K., Kuca, K., Jun, D., Dohnal, V., Dolezal, M. (2006a). Synthesis of the novel series of bispyridinium compounds bearing (i7)-but-2-ene linker and evaluation of their reactivation activity against chlorpyrifos-inhibited acetylcholinesterase. Biorg. Med. Chem. Lett. 16 622-1. 

Alkenes react with bromine to give the products of 1,2-addition. The reaction is classified as an electrophilic addition of bromine, and the two bromine atoms in the product, 1,2-dibromoalkane, are mutually trans. Therefore from the addition of bromine to trans-but-2-ene (2) the product is m o-2,3-dibromobutane (37). This result is explained as follows the initial step is nucleophilic attack by the double bond of the alkene on one bromine, with displacement of the other as bromide ion. The organic intermediate is a bromonium ion 36, whose formation is rationalized in Scheme 4.7. The bromide that was expelled in formation of 36 now becomes a nucleophile and attacks 36 with equal probability at C(2) or C(3). In each case the reaction occurs with inversion of configuration to produce 37. 

The stereochemistry of the cyclopropanation reactions is difficult to predict. (Dimethoxy-phosphoryl)carbene reacts stereospecifically with ( )-l,2-diphenylethene to give 3-dimethoxy-phosphoryl-/ra .v-l,2-diphenylcyclopropane. In contrast, photolysis of (dimethoxyphosphor-yl)(phenyl)diazomethane in the presence of (Z)-but-2-ene gave a mixture of diastereomeric m-isomers, (la,2, 3 )-2 and (la,2a,3a)-2, along with the /ranj-isomer, (la,2ot,3/ )-2, in 15, 3 and 5% yield, respectively. Reaction with ( )-but-2-ene afforded only two of the possible cyclopropanes, namely (la,2, 3 )-2, and (Ia,2a,3/S)-2. ... 

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