Cyclophanes. VII. : Synthesis and Structures of Dioxazolo[3^2]metacyclo(2,5)thiophenophane and a Hihger Homolog

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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 (T_C) of the methylene proton signals is 69℃ and the energy barrier (ΔG^〓) of the conformational change is calculated to be 69.4kJ/mol, which is higher than those of the dioxazolo[3^2]-metacyclophane (1a) and dioxazolo[3^2](2,5)furanometacycophane (3), and (iii) at -31℃, 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.
社団法人日本薬学会の論文
1989-09-25