Annulenes, bridged, benzo

Although most of the fundamental studies of cycl[3.2.2]azines were reported in CHEC(1984) (see Section 12.16.6.3 for leading references), there is continuing interest - synthetic, spectroscopic, and theoretical - in these and their benzo- and dibenzo-fused analogues, all of which may be considered as bridged analogues of [10]-, [14]-, and [18]-annulenes, respectively. The same level of theoretical interest continues to apply to those />m -fused systems with a hypervalent sulfur or selenium at the 5 5 ring junction (Section 12.16.6.6). 

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... 

Most of the compounds discussed in foregoing chapters have been monocyclic although some mention has been made of benzo-annelated derivatives and also, in the preceding chapter, of bridged annulenes and annulenoannulenes, all of which are bicyclic or polycyclic compounds. 

The same effect of benzoannelation is also seen for bridged annulenes thus a benzomethano[10]annulene [149] and a benzometheno-[10]annulene [259] both show reduced diatropicity and a benzo-methano[12]annulene [260] shows reduced paratropicity compared to their non-annelated analogues. 

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