TETRAOXA[24]PORPHYRINOGEN(4.0.4.0) TETRAOXA[22]PORPHYRIN(4.0.4.0) DICATION - A FURTHER ISOMER OF THE AROMATIC 22-PI-TETRAOXAPORPHYRINS/

While the antiaromatic tetraoxa[24]porphyrinogen(2.2.2.2) 1 (trans,cis ,trans,cis) and the corresponding aromatic dication 1(2+) have been pu blished recently, the synthesis of the title compounds is described fo r the first time. Beside the trans,cis,trans-tetraoxa[24]porphyrinogen (4.0.4.0) 2b the isomeric porphyrinogens 2a (hans, cis,cis,trans) and 2c (all-trans in the cisoid conformation) could be isolated. The tetra oxa[22]porphyrin(4.0.4.0) dication is an aromatic 22 pi-system, it exi sts only in the cis,trans,cis,trans-configuration. The dication 2b(2+) can be reduced with tetrakis-N,N-dimethylaminoethene to give pure por phyrinogen 2b. The electrochemistry of the system 2/2b(2+) and AM1 cal culations are described.