REACTIONS OF FISCHER CARBENE COMPLEXES OF 1,6-METHANO[10]ANNULENE

The new Fischer carbene complexes 7, 8, and 10 of 1,6-methano[10]annulene as well as the bis(carbene) complex 15, were readily available in moderate yields by using the classical Fischer method (Schemes 1 and 2). The complexes 5 and 7 reacted easily with several alkynes under benzo-annulation conditions (Dotz reaction). Dapending on the workup conditions, the new benzoquinones 16 and 17 (Scheme 5), hydroquinones 19 and 20 (Scheme 6), and protected hydroquinones 23-25 (Schemes 6 and 7) were synthesized. Surprisingly, in one run we were able to isolate the air-stable [Cr(eta(6)-arene)(CO)(3)] complex 26 (Scheme 7). The X-ray structure and NMR data of 26 established a remarkable perturbation of the 10 pi perimeter of the 1,6-methano[10]annulene part in the hydroquinones 19-26, but no evidence of a sigma-homoaromatic 'bis(trinorcaradiene)' system. The First double Dotz reaction of 15 with hex-3-yne resulted in the formation of the 'anti'-dibenzo-annulated 1,6-methano[10]annulene 32 (Scheme 8), which does not exist furthermore as a pi-homoaromatic system, but as its sigma-homoaromatic valence isomer.