TETRAEPOXY[22]ANNULENE(2.2.2.0) - A TETRA EPOXY-BRIDGED NEUTRAL AROMATIC [22]ANNULENE OF A NEW-TYPE

We describe the synthesis of tetraepoxy[22]annulene(2.2.2.0) 4, the fi rst aromatic annulene of type B by a cyclizing twofold Wittig reaction of 2,2'-bifuran-5,5'-dicarbaldehyde (5) and the bis[phosphonium] salt 8. The configuration of 4, mainly determined by NMR spectroscopy is ( Z,E,Z). According to the UV/VIS spectrum and the H-1-NMR data, the ele ctronic situation in 4 is quite different from that of tetraepoxy[22]a nnulene(3.0.3.0) 2 and tetraepoxy[22]annulene(2.1.2.1) 3. According to variable-temperature H-1-NMR spectroscopy, 4 is a highly dynamic syst em, where the (E)-double bond rotates around the adjacent sigma-bonds. At ca. -130 degrees, this dynamic process is frozen, and 4 appears as a diatropic aromatic system; the free activation energy of the rotati on Delta G double dagger is ca. 5.75 kcal/mol.