Tropone (cyclohepta-2,4,6-trienone) derivatives related to biphenylene. 5H-Benzo[3,4]cyclobuta[1,2]cyclohepten-5-one, 6H-Benzo[3,4]cyclobuta[1,2]cyclohepten-6-one and 7H-Benzo[3,4]cyclobuta[1,2]cyclohepten-7-one

Abstract

Synthetic routes to 5H-benzo[3,4]cyclobuta[1,2]cyclohepten-5-one (6), 6H-benzo[3,4]cyclobuta-[1,2]cyclohepten-6-one (5) and 7H- benzo[3,4]cyclobuta[1,2]cyclohepten-7-one (7), which are analogues of biphenylene in which one benzenoid ring has been replaced by the cyclohepta-2,4,6-trienone (tropone) ring, have been investigated. The tropone (5) was obtained as a stable, crystalline solid and 1H n.m.r, evidence suggests that (5) has a more localized π-bond system in the seven-membered ring than tropone itself. The reactive tropone derivative (7) was generated in solution, and trapped as a _6πs+_4πs cycloadduct with cyclopentadiene.