Hexakisdehydro annulenes

The prototropic rearrangement of the cyclic tetramer 152, the pentamer 153 and the hexamer 154 on treatment with potassium r-butoxide gave the tetrakis-dehydro[24]- (157) , the pentakisdehydro[30]- (159) and the hexakisdehydro[36]-(161) annulenes . Catalytic half-reduction of the triple bonds in 157 and 159 gave [24]annulene (158) and [30]annulene (160), respectively , although their configurations were not firmly established. 

Hexakisdehydro[18]annuIene (178), a [4/i + 2]dehydroannulene having a similar geometry to l,5,9-trisdehydro[12]annulene (172), has been synthesized according to the following sequence of reactions ... 

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