Zusammenfassung
The McMurry reaction of (all-E)-5,5'-([2,2'-bifuran]5,5'-diyl)bis[penta-2,4-dienal] (13) only occurs intramolecularly to give a mixture of the diepoxy[18]annulenes(10.0) 6 and 7. Tetraepoxy[36]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 (ZE,E,Z,E)-configured. The H-1-NMR data confirm that in 6 the ...
Zusammenfassung
The McMurry reaction of (all-E)-5,5'-([2,2'-bifuran]5,5'-diyl)bis[penta-2,4-dienal] (13) only occurs intramolecularly to give a mixture of the diepoxy[18]annulenes(10.0) 6 and 7. Tetraepoxy[36]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 (ZE,E,Z,E)-configured. The H-1-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 sigma-bonds Beginning at -70 degrees, this rotation freezes, and 6 is becoming a diatropic aromatic ring system. Beside [18]annulene itself, (Z,E,Z,E,Z)-diepoxy[18]annulene(10.0) 6 is the only hitherto known [18]annulene derivative with dynamic properties.
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