Annellation of tricarbonylcyclobutadieneiron to the cycloheptatrienyl (tropylium) cation and to cyclohepta-2,4,6-trienone (tropone). Synthesis of some derivatives of (1,7,8,9-h-bicyclo[5,2,0]nonatetraene)tricarbonyliron.

The compounds (1,7,8,9-η-bicyclo[5,2,0]nonatetraenyl hexafluorophosphate)tricarbonyliron (9), (1,7,8,9-η-bicyclo[5,2,0]nona- 1(7),2,5,8-tetraen-4-one)tricarbonyliron (10), and (1,7,8,9-η-bicyclo- [5,2,0]nona-1(7),3,5,8-tetraen-2-one)tricarbonyliron (11) have been prepared. The cation (9) undergoes nucleophilic capture at C2, the position α to the coordinated cyclobutadiene ring. Oxidative removal of the tricarbonyliron group from the symmetrical tropone derivative (10) generates bicyclo-[5,2,0]nona-1(7),2,5,8-tetraen-4-one, which can be trapped as a Diels-Alder adduct with cyclopentadiene.