Diepoxy[18]annulene(10.0) : (Z,E,Z,E,Z)‐Diepoxy[18]annulen(10.0) – ein hochdynamisches Annulen

Diepoxy18]annulenes(10.0): ( Z , E , Z , E , Z )‐Diepoxy18]annulene(10.0) – a Highly Dynamic Annulene The McMurry reaction of (all‐E)‐5,5′‐(2,2′‐bifuran]‐5,5′‐diyl)bispenta‐2,4‐dienal] ( 13 ) only occurs intramolecularly to give a mixture of the diepoxy18]annulenes(10.0) 6 and 7 . Tetraepoxy36]annulene(10.0.10.0) resulting from an intermolecular McMurry reaction is not formed. According to spectroscopic data, 6 is (Z,E,Z,E,Z)‐ and 7 (Z,E,E,Z,E)‐configured. The ¹H‐NMR data confirm that in 6 the (E)‐ethene‐1,2‐diyl bonds (C(11)=C(12) and C(15)=C(16)) rotate around the adjacent σ‐bonds. Beginning at ?70°, this rotation freezes, and 6 is becoming a diatropic aromatic ring system. Beside 18]annulene itself, (Z,E,Z,E,Z)‐diepoxy18]annulene(10.0) 6 is the only hitherto known 18]annulene derivative with dynamic properties.