Chemische Reaktionen mit Fischer‐Carben‐Komplexen des 1,6‐Methano[10]annulens

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 ( Dötz reaction). Depending 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(η 6 ‐arene)(CO) 3 ] complex 26 ( Scheme 7 ). The X‐ray structure and NMR data of 26 established a remarkable perturbation of the 10π perimeter of the 1,6‐methano[10]annulene part in the hydroquinones 19–26 , but no evidence of a σ‐homoaromatic “bis(trinorcaradiene)” system. The first double Dötz 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 π‐homoaromatic system, but as its σ‐homoaromatic valence isomer.