8,19-DIMETHYL-TETRAEPOXY[22]ANNULENE(2.1. 2.1) - THE FIRST TETRAEPOXY-BRIDGED AROMATIC [22]ANNULENE

By McMurry reaction of 5,5'-ethylidenebis[furan-2-carbaldehyde] (15), a syn/anti mixture 16 of (E,E)- and -8,19-dihydro-8,19-dimethyl-tetrae poxy[22]annulene is obtained. The (E/E)-isomers 16 are the first rotat ionally active noncyclic conjugated macrocycles, where the (E)-ethened iyl moieties rotate around the connecting single bonds. The dihydro-te traepoxy[22]annulenes 16 are dehydrogenated by (Ph3C)BF4 as well as by O-2 to give the tetraepoxy[22]annulene 11. The spectroscopic data sup port the character of 11 as an aromatic, diatropic ring system, which is rather sensitive towards O-2. In the oxidation mixture obtained fro m 11, beside polymeric products, two compounds 19 and 20 can be isolat ed, carrying one and two CHO groups, respectively, resulting by oxidat ion of one or both Me-groups but having retained the aromatic 22 pi sy stem of 11.