Synthesis, characterization, and crystal structures of two strained cyclic diacetylenes and their precursors

The synthesis, characterization, and crystal structures of two novel strained cyclic diacetylenes are reported. A discussion is presented about the relative bond distances of the diacetylenes compared to a previously reported strained cyclic diacetylene to further determine the degree of aromaticity of that compound. 1,2:5,6:9,10:13,14-Tetrabenzo-3,7,11,15,17-pentadehydro[18] annulene (5) is triclinic, P(-)1, with alpha = 9.489(5), b = 10.550(5), c = 12.155(6) Angstrom, alpha = 100.50(4), beta = 106.50(4), gamma = 100.85(4)degrees. 1,2:5,6:9,10:13,14:17,18-Pentabenzo-3,7,11,15,19,23,25-heptadehydro[26]annulene (7) is triclinic, P(-)1, with a = 9.611(2), b = 10.388(3), c = 15.963(3) Angstrom, alpha = 88.67(2), beta = 76.25(1), gamma = 68.69(2). In addition, two precursors of 5, 3 and 4 which have a helical twist, are reported. [1,2-ethynediyl-bis(2,1-phenylene-2,1-ethynediyl-2, 1-phenylene-2,1-ethynediyl]bis[trimethyl-silane] (3) is monoclinic, P2(1)/c, with a = 13.682(4), b = 9.787(2), c = 13.448(4) Angstrom, beta = 112.37(2)degrees. 1,1'-(1,2-ethynyldiyl)bis[2-[(2-ethynylphenyl)ethynyl]-benzene (4) is monoclinic, P2(1)/n, with a = 15.951(3), b = 3.999(1), c = 18.168(4) Angstrom. beta = 99.05(3)degrees.