3,9,15-Tris(p-tert-butylphenyl)dodecadehydro[18]annulene (6) and 3,6,9,12,15,18-hexa-substituted dodecadehydro[18]annulenes (7, 8, and 9) have been prepared. These compounds were shown to be heated up to 150 °C without decomposition. The molecular structure of 7 was determined by X-ray crystallography, which showed that 7 has a planar π-system with D6h-symmetry. The UV and NMR spectral data indicate