Hexamethylene bridged cycloheptatrienes and tropone

The novel, bridged bromocycloheptatriene (4) is obtained by the thermolysis of a tricyclo6.4.1.0^1,8]tridecane derivative (6), and the observed anti stereochemistry of the Br atom on C(13) is accounted for by assuming the suprafacial 1,5] hydrogen shift in the intermediate 7. The mother hydrocarbon (8) and syn-methyltropylidene (9), as well as tropone (10), are derived from 4, and the structures of these products are examined spectrometrically. The covalent CBr bond of 4 remains intact under various reaction conditions of nucleophilic substitution, and this is ascribed to the conformational rigidity constrained by the short hexamethylene bridge. The attempted transformation of 4 or 10 to the corresponding tropyllium ion 12 or 14 fails to success and this is again attributed to the bridge effect.