4,8-bridged bicyclo octa-2,5-dienes

When a small ring was fused to the bridge of TBP precursor 44a, strained cycloalkene would be formed in the rDA reaction. Thus, the rDA temperamre was expected to be raised in this case. Such precursors were prepared from cycloheptatriene 49e [55] and cyclooctatriene 49f [56]. The DA reaction of these diene equivalents with disulfonylethy-lene 4b proceeded via norcaradiene and bicyclo[4.2.0]octa-diene forms to give the tricyclo adducts 51e and 51f, which were transformed to precursors 53e-H2 and 53f-H2 in the usual manner (T. Okujima et al., manuscript in preparation). The rDA temperatures of 53e-H2 and 53f-H2 were proved to be extremely raised. Cyclopropane-fused 53e-H2 and cyclo-butane-fused 53f-H2 did not undergo the thermal rDA reaction below 265 and 180 C, respectively, and were successfully metallated with Cu(OAc>2 to give 53e-Cu and 53f-Cu (T. Okujima et al., manuscript in preparation). 

In contrast to norbornadiene, bicyclo[2.2.2]octa-2,5-diene does not always give the transan-nularly bridged products in normal solution reactions, whereas in the anodic electrooxidation this nonconjugated octadiene showed the formation of products, mainly tricyclo-[2.2.2.0 ]octane derivatives 5 and 6 from transannular interaction, exclusively. ... 

Gross and coworkers demonstrated that both Cf Hi2+ isomers reside in distinct potential wells and can be characterized by CID in both sector-field and FT-ICR mass spectrometers. The mass spectrometric experiments were in line with calculation in that the ionized bicyclic isomer appears to be more stable than 4-vinylcyclohexene ions, and with the radiolytic results in that a closely related bicyclic isomer, viz. ionized bicy-clo[2.2.2]octene, is not easily formed upon ionization of the other CgHn hydrocarbons. The retro-Diels-Alder reaction ionized bicyclo[2.2.2]octa-2,5-dienes leading to expulsion of the initially saturated bridge as an alkene gives rise to the base peak in the El spectra . ... 

The bridged heterocycles (4 X = S, Se, or Te) have been prepared from the dibromides. Compound (4 X = Te), which extruded tellurium on heating, did not give the expected bicyclo[3,3,0]octa-2,6-diene, but instead gave the fluxional bicyclo[5,l,0]octa-2,5-diene. ° ... 

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