Tricyclo nonene

Acetoxy-6-oxo-l,4-dimethyl-tricyclo 3.2.2.02[Pg.660]

At higher temperatures (290°C), the 4.2.1 triene gives c/5 -8,9-dihydroindene by at least two pathways, the dominant of which (70%) results from an intramolecular Diels-Alder reaction to tetracyclo[4.2.1.0. 0 ]nonene followed by a homo-1,5-hydrogen shift to give tricyclo[4.3.0.0 ]nona-4,7-diene followed by another homo-1,5-hydrogen shift as revealed by deuterium and carbon-13 labeling in separate experiments summarized in Scheme 10.22. ... 

Dimethylenecyclobutene has been prepared by thermolysis of 1,4-dimethylene-tricyclo[4,2,l,0 ]nonene (151), which is itself available from the addition product of quadricyclane and maleic anhydride. The benzocyclobutene analogues of (151) do not decompose thermally to give benzocyclobutadiene. Both exo- and endo-epimers (152) and (153) give (154), the product of intramolecular [2 + 2] addition. Under the same conditions, saturated e do-benzocyclobutene (155) rearranges to its exo-isomer (157). 

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