Macrocyclic [4n+2]-Huckel aromatic systems up to n = 9 and [4n] antiaromatic systems up to n = 10: Homologous sequences from tetraepoxy[24]annulene(2.0.2.0) to tetraepoxy[40]annulene(12.0.12.0) and from the 'tetraoxa[22]porphyrin(2.0.2.0)'- to the 't

摘要

Tetraepoxy[32]annulene(8.0.8.0) 3, tetraepoxy[36]annulene(10.0.10.0) 4, and tetraepoxy[40]annulene(12.0.12.0) 5 are synthesized and oxidized to give the 'tetraoxa [30]-', 'tetraoxa [34]-', and 'tetraoxa[38]porphyrin' dications 8-10. The annulenes as well as the 'porphyrins' are mixtures of at least two different configurational isomers, which can be analyzed by H-1-NMR techniques. Together with systems described already earlier, a complete homologous sequence from tetraepoxy[24]annulene(2.0.2.0) to tetraepoxy[40]annulene(12.1.12.0) and from 'tetraoxa[22]porphyrin(2.0.2.0)' to 'tetraoxa[38]porphyrin(12.0.12.0)' dications are available for the First time. The UV/VIS-absorption maxima in the annulene series are shifted to longer wavelengths with an increment of 12 nm per additional C=C bonds, and the Delta delta values of the H-1-NMR spectra demonstrate a decreasing paratropic character (Delta delta = 5.97 (1), 2.80 (3), and 4.23 ppm (4)). The averaged lambda(max) values of the Sorer bands of the 'tetraoxaporphyrin' dications show a linear bathochromic shift with an increment Delta lambda of 58 nm per two additional double bonds, the absorptions of the most intensive Q-bands also increase linearly with an increment of ca. 160 nm. The Delta delta values of the H-1-NMR spectra of the 'tetraoxaporphyrin' dications are increasing with the ring size (Delta delta = 24.04 (7a) to 25.17 (9a) ppm), respectively, decreasing (Delta delta = 21.55 (6) to 21.50 (9b) ppm) with a small maximum of 22.60 ppm for 7b, depending on the configuration of the isomers. The results confirm the antiaromatic character of the annulenes with up to 40 pi electrons and the aromatic character of the 'tetraoxaporphyrin' dications with up to 38 pi electrons. [References: 44]