1989 Volume 37 Issue 9 Pages 2303-2306
The title compound (6) was synthesized by the one-pot coupling reaction of 1, 3-bis(2-isocyano-2-tosylethyl)benzene (4) with thiophene-2, 5-dicarbaldehyde (5), along with the higher homolog (7). On the basis of proton nuclear magnetic resonance (1H-NMR) spectra at various temperatures, it was considered that (i) the conformational change of 6 at room temperature was strongly erstricted because of the observation of very broad signals in both aromatic and aliphatic regions, (ii) the coalescence temperature (TC) of the methylene proton signals is 69°C and the energy barrier (ΔG〓) of the conformational change is calculated to be 69.4kJ/mol, which is higher than those of the dioxazolo[32]-metacyclophane (1a) and dioxazolo[32](2, 5)furanometacycophane (3), and (iii) at -31°C, 6 exists in two fixed conformers, i.e., syn and anti forms because of the observation of a set of the oxazole C2-H signals. These results suggest that the rigidity of the thiophene-containign heterophane 6 is due to the bulkiness of the large sulfur atom as well as the presence of a longer carbon-sulfur bond.