Syntheses of Alkyl Substituted Bis-oxido-bridged [15] annulenones

Abstract

Methyl substituted bis-oxido-bridged [15] annulenones III and VIII, n=3 members of [4n+3] annulenone, were prepared starting from 2, 15-dimethoxycarbonyl-[15] annulenone I. Annulenones III and VIII have no appreciable amount of a diamagnetic ring current due to the nonplanar conformations. On the contrary, VI and XI sustain a strong diamagnetic ring current as a consequence of the delocalized14π electron system, whose planarity is enforced by ring formation. On protonation, annulenone III and VIII were converted into stable annulenium ions IIIa and VIIIa, respectively.