Annulenes, dehydro, benzo

The known bridged [18]annulenes are also diatropic as are most of the known dehydro[18]annulenes. The dianions of open and bridged [16]annulenes are also 18-electron aromatic systems, and there are dibenzo[18]annulenes. [22]Annulene and dehydro[22]annulene are also diatropic. A dehydro-benzo[22]annulene has been prepared that has eight C=C units, is planar and possesses a weak induced ring current. In the latter compound there are 13 outer protons at 6.25-8.45 5 and 7 inner protons at 0.70-3.45 8. Some aromatic bridged... 

Marsden JA, Palmer GJ, Haley MM (2003) Eur J Org Chem 2355-2369 Synthetic strategies for dehydro-benzo[n] annulenes... 

These proposed benzo-fused dehydro [8] annulenes can generally be accessed via a bromination-dehydrobromination synthetic pathway. As shown in Scheme 5.1, upon bromination under irradiation, dibenzo[a,e]COT (19) was converted into dibromo and tetrabomo compounds 20 and 21, which then underwent dehydro-bromination with f-BuOK to give stable dibenzo[ ,e]cyclocta-l,3,5-trien-7-yne... 

Scheme 5.1 Synthesis of benzo-fused dehydro[8]annulenes 11 and 12.

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