Trans-bicyclo nona-3,7-diene

Surprisingly, /ranj-tris-a-homobenzene (eni/o/exo-tetracyclo[6.1.0.0 . 0 ]nonane), and its hexamethyl derivative, at elevated temperatures (380-400°C in a flow system and 120°C, respectively) rearrange to frani-bicyclo[4.3.0]nona-3,7-diene and hexamethyl-rra 5-tricyclo[4.3.0.0 ]non-3-ene. It was shown by isotopic labeling, however, that this rearrangement also proceeds by way of a [ 2 + A -t- cycloreversion, which in these cases leads to highly reactive cis,trans,trans-cyclonona-l,4J-tnenes, which undergo a subsequent intramolecular [2-1-2] cycloaddition. ... 

The metal-catalyzed dimerization of norbornadiene was discovered in 1961 by two independent groups of workers (3, 4) and since then has received considerable attention by others. The various possible dimers are shown in Table II. Excluding structures in which the cyclobutane ring is fused, trans, 14 dimers (XXIII-XXXVI) are possible, of which seven have been isolated. The structures of six are now rather well established. Initially (3) the structure of one dimer was considered to be (XXXVII). In the meantime NMR measurements (44) and synthetic studies (45, 46) have shown that (XXXVII) is (XXV), the liquid exo-trans-endo dimer. Pyrolysis of both (XXV) and (XXIII) (m.p. 67-68°) yields cyclopentadiene and a mixture of bicyclo[4.2.1]nona-2,4,7-triene (XXXVIII) and exo-tricyclo[4.2.1.02 ]nona-3.7-diene (XXXIX) (46). The exo-trans-endo isomer (XXV) decomposes more... 

The same mixture of compounds was obtained from pyrolysis of trans-, 9-dihydroindene. Since the major products were not obtained upon pyrolysis of bicyclo[6.1.0]nonatriene, it is clear that this material and bicyclo[5.2.0]nonatriene and all c/ -cyclononatetraene or its c,t,c,c or t,c,c,c isomer are not involved in these thermal isomerizations (see Section 2.1). It would appear reasonable that 1,5-hydrogen shifts could convert the rra/i5 -8,9-dihydroindene to the major product and ultimately to the other products however, not clear is how the tetracyclononene is converted to rra/i5 -8,9-dihydroindene. This latter material could undergo a concerted or stepwise homo-3,3-shift to tricyclo[4.3.0.0 ]nona-4,7-diene, but progress from there to fra/i5 -8,9-dihydroindene is not obvious (Scheme 10.25). 

The parent trans isomer was found to give rran -bicyclo[4.3.0]nona-3,7-diene with log k = 13.39 - 42000/2.37 r. Pyrolysis of the 3,6- C material gave the bicyclic compound with labels at C2, C3, and C8 in a 0.5 0.5 1.0 ratio suggesting the intermediacy of cis, trans, trans-1,4,7-cyclononaihene formed by a concerted retro 2 -h 2 + 2 cyclization followed by a 2s + 2a cycloaddition to a transfused tricyclo[4.3.0.0 ]non-3-ene which undergoes the usual non-concerted conversion of bicyclo[2.1.0]pentane to cyclopentene (see Chapter 6, Section 1) (Scheme 10.70). ... 

Knott, P.A. and MeUor, J.M., Photochemical rearrangement of bicyclo[3.3.1]nona-3,7-diene-2,6-diones,/. Chem. Soc., Perkin Trans. 1,1030, 1972. 

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