Tetrakisdehydro annulenes

Recently, some tetrakisdehydro[18]annulenediones (201-204) have been synthesized --The electrochemical reduction of 201, 203 and 204 clearly indicates that these annulenediones are indeed quinones derived from the aromatic tetra-kisdehydro[18]annulene . 

The preparation of annelated tetrakisdehydro[18]annulenes 349 and 350 and the reference dehydroannulene 351 afforded further insight into the 7t-electron delocalization in annelated annulenes . When a dihydronaphthalene nucleus in 351 was replaced by naphthalene to form the annelated dehydroannulene 350, an appreciable suppression of diatropicity in 350 was observed. Further replacement of the dihydronaphthalene by naphthalene to give the dinaphtho-annelated derivative 349 resulted in a further suppression of the diatropicity in contrast to the increase of diamagnetic ring current in the case of transition from 342 to 340 and from 343 to 341. 

At the same time, the synthesis of a condensed system consisting of two acetylene-cumulene tetrakisdehydro[18]annulenes has been reported by Nakagawa and his coworkers . ... 

Another tetrakisdehydro[14]annuleno[14]annulene (LXI) is of some interest because two different types of bisdehydro[14]annulene are fused together, the B ring being of the sort which in either Kckulc form contains a triple bond and an allenic system [272]. 

The electrochemical reduction of (XXIX) [101], a 2,ll-bisdehydro[18]-annulene-1,10-dione [102], and of 2,4,11,13-tetrakisdehydro[18]-annulenc-1,6-diones and 2,4,11,13-tetrakisdehydro[18]annulene-l,10--diones [103,104] is consistent with the reduction behaviour of quinones. They are more easily reduced than is benzoquinone, possibly because there is less electrostatic repulsion between the resultant negatively charged oxygen atoms in the products, since they are further apart than in a six-membered ring. The [16]dione (XXX) is less easily reduced than the [18]diones this could either reflect that reduction in this case leads to a 4u TT-electron system rather than a (4n+2) system, or it may be due to the greater proximity of the oxygen atoms in (XXX) [104]. 

An example of an annulenoannulene with one bond common to both rings is the following tetrakisdehydro[14]annuleno[14]annulene [270] ... 

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