Isomerization of the bicyclo[5.1.0]octadienyl anion: (Short communication)

NMR spectroscopy has revealed that the bicyclo[5.1.0]octadienyl anion 2 isomerizes by opening of the three‐membered ring and a 1,2 shift of hydrogen to the 1,6‐methanoheptatrienyl anion 3. The symmetry‐forbidden electrocyclic ring opening of 2 to the cyclo‐octatrienyl anion 5 does not occur. Experiments with cyclo‐octa‐1,3,5‐triene showed that 5 is unstable relative to disproportionation into cyclo‐octatriene and cyclo‐octatetraenyl dianion.