Dimerization strained hydrocarbons

Roth, Schilling and coworkers [47-54] have investigated the nuclear spin polarization behavior of cation-radicals of numerous strained hydrocarbon systems produced by PET to strong electron acceptors such as chloranil, anthraquinone and cyanoaromaties. These systems include cyclopentadiene dimers, methyl-enebicyclo[2.2.0]hexenes [48], bicyclo[1.1.0]butanes [49], hexamethyl (Dewar benzene) [50], norbomadiene [53], quadricyclene [53], and 1,2-diphenylcyclopropanes [54]. 

Two transition metal catalyzed [27t + 2strained hydrocarbons, reacts with exo-tricyclo[3.2.1.0 " ]oct-6-ene (5) to give tetracyclo[3.3.0.0 .0 ]octane (6) in quantitative yield. The endo-isomer is unreactive. ... 

Many other ion-molecule reactions involving highly unsaturated hydrocarbon ions and neutral olefins or the equivalent strained cycloalkanes have been studied by mass spectrometry98. For example, we may mention here the addition of ionized cyclopropane and cyclobutane to benzene radical cations giving the respective n-alkylbenzene ions but also isomeric cyclodiene ions such as ionized 8,9-dihydroindane and 9,10-dihydrotetralin, respectively. Extensive studies have been performed on the dimerization product of charged and neutral styrene4. 

Thus, they prevent an arrangement of the spindle apparatus. The tubuline-benzimidazole-interactions have been studied in detail (.6). It is known that carbendazim, for example, after entering the nucleus, specifically binds to the 3 -subunit of tubuline and by this inhibits the dimerization of the a and 3 -subunits to a functional tubuline unit. Resistant strains possess altered 0 -subunits with a decreased affinity for benzimidazoles (7). The modes of action of other inhibitors of mitosis, like dicarboximides, aromatic hydrocarbons, or dithiocarbamates, have not yet been precisely described on a molecular basis. 

Bicyclo[3.2.0]hept-l-ene (151) can be prepared from the tosylhydrazone of norbornan-7-one via norbornan-7-ylidene 150 in 74% as a stable olefin (144). Similarly, 152 has been obtained from norborn-2-en-7-one in a yield of 67% (144a). Introduction of a further double bond leads to the strained triene 153, which has been prepared from 105b (Scheme 3). Compound 153 dimerizes readily at room temperature to a 1 1 mixture of hydrocarbons 154 (145). The most likely structures of these dimers arise from a formal [2 + 2]cycloaddition of the bridgehead double bonds of 153 with each other. Support for the intermediacy of 153 comes from trapping experiments with 1,3-diphenyl-isobenzofuran, which yield a mixture of stereoisomers via reaction with the bridgehead double bond of 153. 

Diels-Alder reaction of the highly strained alkene (48) with benzene is one of the strikingly unusual reactions. The driving force of the unusual cycloaddition would be a favorable electron transfer from benzene to the low-lying LUMO of the highly electron-deficient double bond of 48 [15]. In contrast, the corresponding hydrocarbon (50) dimerizes and polymerizes rapidly at ambient temperature (Scheme 1.43) [16]. 

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