- Controlled radical polymerization of 3-methylenecyclopentene with N-substituted maleimides to yield highly alternating and regiospecific copolymers
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High-molecular-weight diene copolymers with a regiospecific repeating structure were produced in a high yield during the alternating radical copolymerization of N-substituted maleimides (RMIs) and 3-methylenecyclopentene (MCP) as the cyclic 1,3-diene monomer including a reactive exomethylene moiety. The eminent copolymerization reactivity of MCP was in contrast to the predominant occurrence of the Diels-Alder reaction of isoprene with the RMIs rather than copolymerization. The highly alternating structure of the copolymers was confirmed based on the monomer reactivity ratios for the copolymerization of MCP (M1) and N-phenylmaleimide (PhMI, M2), r 1 = 0.010 and r2 = 0.0080. A mechanism for the highly controlled 1,4-regiospecific propagation, which consists of the addition of an RMI radical to the exomethylene group of MCP and subsequent 1,4-regiospecific propagation, was supported by the DFT calculations using model reactions as well as the precise structure determination of oligomers produced during telomerization in the presence of 1-butanethiol as a chain transfer agent. The resulting copolymers exhibited no weight-loss under 340 C during heating in a nitrogen atmosphere and their glass transition temperature was over the wide temperature range of 66-159 C, depending on the structure of the N-alkyl substituents. The transparent and flexible films were fabricated by a casting method. The optical properties of the films were as follows: the visible light transmittance over 95% at 380 nm, the refractive indices of 1.54-1.58, and the Abbe number of 42-45.
- Yamamoto, Daisuke,Matsumoto, Akikazu
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p. 9526 - 9536
(2014/03/21)
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- Flash vacuum pyrolysis over magnesium. Part 1 - Pyrolysis of benzylic, other aryl/alkyl and aliphatic halides
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Flash vacuum pyrolysis over a bed of freshly sublimed magnesium on glass wool results in efficient coupling of benzyl halides to give the corresponding bibenzyls. Where an ortho halogen substituent is present further dehalogenation gives some dihydroanthracene and anthracene. Efficient coupling is also observed for halomethylnaphthalenes and halodiphenylmethanes while chlorotriphenylmethane gives 4,4′-bis(diphenylmethyl)biphenyl. By using α,α′-dihalo-o-xylenes, benzocyclobutenes are obtained in good yield, while the isomeric α,α′-dihalo-p-xylenes give a range of high thermal stability polymers by polymerisation of the initially formed p-xylylenes. Other haloalkylbenzenes undergo largely dehydrohalogenation where this is possible, in some cases resulting in cyclisation. Deoxygenation is also observed with haloalkyl phenyl ketones to give phenylalkynes as well as other products. With simple alkyl halides there is efficient elimination of HCl or HBr to give alkenes. For aliphatic dihalides this also occurs to give dienes but there is also cyclisation to give cycloalkanes and dehalogenation with hydrogen atom transfer to give alkenes in some cases. For 5-bromopent-1-ene the products are those expected from a radical pathway but for 6-bromohex-1-ene they are clearly not. For 2,2-dichloropropane and 1,1-dichloropropane elimination of HCl occurs but for 1,1-dichlorobutane, -pentane and -hexane partial hydrolysis followed by elimination of HCl gives E, E-, E,Z- and Z,Z- isomers of the dialk-1-enyl ethers and fully assigned 13C NMR data are presented for these. With 6-chlorohex-1-yne and 7-chlorohept-1-yne there is cyclisation to give methylenecycloalkanes and -cycloalkynes. The behaviour of 1,2-dibromocyclohexane and 1,2-dichlorocyclooctane under these conditions is also examined. Various pieces of evidence are presented that suggest that these processes do not involve generation of free gas-phase radicals but rather surface-adsorbed organometallic species.
- Aitken, R. Alan,Hodgson, Philip K.G.,Morrison, John J.,Oyewale, Adebayo O.
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p. 402 - 415
(2007/10/03)
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- Photoisomerization of bicyclopropylidene and 1,2-dimethylenecyclobutane in rare-gas matrices: Towards the IR-spectroscopic identification of tetramethyleneethane (2,3-dimethylenebutane-1,4-diyl)
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Bicyclopropylidene (3) and 1,2-dimethylenecyclobutane (7) have been irradiated in rare-gas matrices. If 1,2-dimethylenecyclobutane (7) is exposed to the light of a KrF excimer laser (λ = 248 nm), an isomeric species is produced, showing an absorption at 793.1 cm-1 (argon matrix) or 791.2 cm- 1 (xenon matrix) in the IR spectrum. The back reaction can be induced with light of k λ = 254 nm. This photochemical interconversion, together with the comparison between the experimental and calculated band positions, supports the assignment of the IR absorption near 790 cm-1 to tetramethyleneethane (5).
- Maier, Guenther,Senger, Stefan
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p. 1291 - 1294
(2007/10/03)
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- Central and Lateral Bicyclo[1.1.0]butane Bond Cleavage with Subsequent Wagner-Meerwein Rearrangements or Carbene Formation in the 185-nm Photolysis of Tricyclo[3.1.0.02,6]hexane, Tricyclo[4.1.0.02,7]heptane, and Tricyclo[5.1.0.02,8]octane
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The 185-nm photochemistry of tricyclop[3.1.0.02,6]hexane, tricyclo[4.1.0.02,7] heptane, [1,7-d2]tricyclo[4.1.0.02,7]heptane, tricyclo[5.1.0.02,8]octane, and [1-d]tricyclo[5.1.0.02,8]octane was investigated. Tricyclo[5.1.0.02,8]octane yields bicyclo[4.2.0]oct-7-ene, tricyclo[4.1.0.02,7]heptane yields 85% bicyclo[3.2.0]hept-6-ene and 15% 3-methylenecyclohexene, and tricyclo[3.1.0.02,6]hexane yields 39% 3-methylenecyclopentene, 15% 1,3-cyclohexadiene, 26% trans-1,3,5-hexatriene, and 20% cis-1,3,5-hexatriene. From the deuterium-labeling studies, it is concluded that, in the case of the tricyclooctane, the central bicyclobutane bonds cleave in the primary step to give radical cationic or zwitterionic species that undergo a Wagner-Meerwein rearrangement. Also, in the case of tricycloheptane, this is the dominating pathway but lateral C-C bond cleavage with subsequent carbene and product formation takes place to the extent of ca. 15%. For tricyclohexane, this pathway becomes the major route. Our photomechanistic observations are in good agreement with earlier theoretical investigations on the relative energetic ordering of the bicyclobutane HOMOs, in that the product composition reflects this.
- Adam, Waldemar,Alt, Christine,Braun, Max,Denninger, Uwe,Zang, Gerald
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p. 4563 - 4571
(2007/10/02)
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- On the Thermal Isomerization and Aromatization of Hex-1-ene-5-yne
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The gas phase conversion of hex-1-ene-5-yne induced by conventional hot-wall pyrolysis, very low pressure pyrolysis (VLPP-MS technique) and continuous-wave CO2 laser-photosensitized (SF6) pyrolysis was studied at 350-1100 deg C.The pyrolysis experiments were performed in quartz reactors and the reaction products analyzed by capillary gas chromatography, mass and n.m.r. spectroscopy.The pattern of conversion suggested for all the processes involved a sequence of isomerizations ( -> hexa-1,2,5-triene -> methylcyclopentenes), aromatization (into benzene via pentafulvene) and C-C bond rupture (into propargyl and allyl radicals).The formation of benzene is explained by reaction network with methylenecyclopentenes and methylcyclopentadienes as key intermediates.
- Remmler, M.,Ondruschka, B.,Vorwerk, D.,Olk, B.,Pola, J.,Kubat, P.
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p. 699 - 709
(2007/10/02)
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- Carbene Rearrangements, X. 2-Vinylcyclobutylidene
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The Bamford-Stevens reaction of 2-vinylcyclobutanone tosylhydrazone sodium salt (13) has been studied with respect to the potential carbene-carbene rearrangement 3 -> 4. 2-Vinylcyclobutylidene (3) surprisingly undergoes exlusively carbene rearrangements.In 3 the cyclobutylidene-methylenecyclopropane rearrangements to 16 and 17 dominate.The 1,3-carbon migration of the divalent carbon is not observed.
- Brinker, Udo H.,Koenig, Lothar
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p. 882 - 893
(2007/10/02)
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- Reactions of Methylenecyclopropanes, VI. Palladium(0)-catalyzed Cycloadditions of 1-Methylene-2-vinylcyclopropane
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1-Methylene-2-vinylcyclopropane (1) is cyclodimerised at palladium(0)/triisopropylphosphane catalysts to give the carbocycles 3 - 5, which in certain cases are obtained as Z/E-isomers.In the presence of norbornene codimerisation occurs, which leads to the
- Binger, Paul,Germer, Alfred
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p. 3325 - 3335
(2007/10/02)
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