Isomerization tricyclo hexane

The thermolysis of ladderanes has been studied in detail (Scheme 1). On heating, bicyclo[2.2.0]hexane and its derivatives exhibit skeletal inversion and cleavage to 1,5-hexadiene derivatives.26 The thermolysis of anti- and yyft-tricyclo[4.2.0.02,5]octanes and their derivatives gives cis,cis- and cis, trans-1,5-cyclooctadienes, cis- and trans-1,2-divinylcy clobutanes, and 4-vinylcyclohexene as ring-opening products.27-29 Furthermore, syn-tricyclo-[4.2.0.02,5]octane isomerizes to aw//-tricyclo[4.2.0.02,5]octane.29c,d The thermodynamic parameters and the reaction mechanisms for these thermal reactions have been discussed. 

The ra s-tricyclo[3.1.0.02-4]hexane derivatives, prepared according Eq. 15, are easily isomerized by some Rh(I) catalysts to give tram-1,2- and 1,3-divinylcyclobutane derivatives 72) (Eq. 19). 

Besides polymeric material, a mixture of three ene reaction products is obtained (18% combined yield) in the thermal reaction, which proceeds at 20°C within several minutes. Similar results are found when zeolites with a large pore diameter (5-13 A) are used as catalysts. After irreversible addition of the cyclopropene to the zeolite, only polymeric material is obtained. Zeolites with 3- or 4-A pores give rise to a product spectrum similar to that obtained with phosphane-free palladium(O) catalyst systems, i.e. 90-97% of the tricyclic dimers are formed from 1- or 3-methylcyclopropene at temperatures between — 35 and 35 C. The palladium(II) chloride catalyzed reaction almost quantitatively yields a 2 1 mixture of the isomeric 1,2- and l,4-dimethyl-evo-tricyclo[3.1.0.0 ]hexane (lA and IB) from 1-methylcyclopropene. The reaction is strongly exothermic and therefore must be carried out in dilute solutions with effective... 

The room temperature stable 1,3,3-trimethylcyclopropene, which because of geminal disubstitution cannot undergo any ene reaction, can react analogously. On treatment with di-jW-chloro-bis[(r -allyl)palladium], a 10% yield of the two isomeric dimers, 1,2,3,3,6,6- and 1,3,3,4,6,6-hexamethyl-exf)-tricyclo[3.1.0.0 ]hexane (2A and 2B), is obtained, along with large amounts of polymeric material. 

Of the photochemical conversions of 3,6-bridged cyclohexa-1,4-dienes to 3,6-bridged syn-tricyclo[3.1.0.0 ]hexanes, the light-induced isomerization of norbornadienes to quadricyclanes (see Houben-Weyl, Vol.4/5a, pp 232-237) has been most intensively studied. The parent hydrocarbon, quadricyclane (1, tetracyclo[3.2.0.0 . 0 ]heptane) has become available on a preparative scale by acetophenone sensitized isomerization of norbornadiene (bicyclo [2.2.1]hepta-2,5-diene). ... 

The remarkable tricyclo-octanes shown below have recently been synthesized (Avram et al., 1964). They both yield 1,5-cyclo-octadiene on pyrolysis at 150° C which suggests that the kinetic parameters for these isomerizations cannot be two dissimilar to those for the isomerization of bicyclo[2,2,0]hexane. 

On the other hand, R-exchanged zeolites have also been used in combination with a metal function, for carrying out the isomerization and hydrocracking of paraffins and cycloalkanes. This is the case for isomerization of n-hexane to isohexane and 2,2-dimethyl-butane (Rabo et al. 1961) the isomerization of n-undecane to mixed Ci 1 isomers at 275°C on Pt/Ce-Y zeolite (Weitkamp et al. 1985) the isomerization of c (7o-exo-tricyclo[5.2.1.02,6]-decane or exo-tricyclo[6.2.1.02,7]-undecane into adamantane or 1-methyladamantane, respectively, on R-Y at 150-270°C (Lau and Maier 1987) the isomerization of tetrahydrodicyclopentadiene into adamantane on Re-Y in a H2/HC1 atmosphere at 250°C (Honna et al. 1986) or the double bond relocation of 2-alkyl acrolein into fran.j-2-methyl-2-alkenals over Ce,B-ZSM-5 (Fisher et al. 1986). Recently, it has been reported that Ce-promoted Pd/ZSM-5 is an active and selective catalyst in the dehydroisomerization of a-limonene to / -cymene (Weyrich et al. 1997). 

Remarkably, the thermal isomerization of tricyclo[3.1.0.0 ]hexane gives all-cw-l,3-cyclohexadiene (Scheme 5.5). Interestingly, the activation energy (log k = 13.6 — 41700/2.3Rr) is similar to that of the parent molecule. " ... 

Martin and Eisenmann have re-investigated the thermolysis of syn- and anti-tricyclo[4,2,0,0 ]octane (511) and (512). Both ultimately give cis,cis-cyclo-octa-l,5-diene but the re-investigation shows that cis,trans-octa-l,5-diene is also produced and that it isomerizes to the all-cis-diene under the reaction conditions. The cis,trans-diene was trapped with hexachlorocyclopentadiene, and was also characterized as its dimer or its silver nitrate complex. Both (511) and (512) give mixtures of cis,cis-and cis,trans-octadiene in a co. 3 5 ratio. Thus the single-inversion pathway usually found in the pyrolysis of bicyclo [2,2,0] hexanes is also followed, at least partially, by... 

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