Synthesis and Properties of Kinetically Stabilized Cyclohepta[def]fluorene Derivatives

The dihydrocyclohepta[def]fluorene 18 was prepared by starting from 2,7‐di‐tert‐butylfluorene (11). Deprotonation of 18 furnished the dianion 32− in which the charge is mainly localized at the five‐ and seven‐membered rings as evidenced by NMR investigations. Attempts to oxidize 32− to the uncharged species 3 failed. The ketones 26 and 29 were obtained by regioselective oxidation of 18. Deprotonation of 29 and 26 furnished the anions 4 and 5, respectively, which could be described as cyclohepta[def]fluorenes with a strong donor substituent. 13C‐NMR spectroscopic investigations, however, revealed that 4 is described best as an acyl‐substituted fluorenyl anion. In contrast to this, proof of the existence of the anion 5 could be obtained only from a trapping experiment.