Cyclophanes. V. : Synthesis and Conformational Analysis of Novel Heterocyclophanes Containing 2,5-Bis(5-oxazolyl)furan Units

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Two novel heterocyclophanes, dioxazolo[3^2](2,5)furanometacyclophane (5) and the higher homolog (6) possessing 2,5-bis(5-oxazolyl)furan units, were synthesized by the one-pot coupling reaction of 1,3-bis(2-isocyano-2-tosylethyl)benzene (3) with furan-2,5-dicarbaldehyde (4). On the basis of the variable-temperature nuclear magnetic resonance (VT-NMR) spectra of 5,the conformations in solution both at room temperature and at -18℃ could be assigned as a syn form, and the energy barrier (ΔG^〓) for the conformational flipping at the coalescence temperature (T_c=12℃) was determined to be 58.0 kJ/mol, which is lower than that of dioxazolo[3^2]metacyclophane (1a). Therefore, it was suggested that the oxygen atom of 5 with its lone pair is less bulky with respect to the conformational change than the aromatic carbon-hydrogen bond of 1a.
社団法人日本薬学会の論文
1989-05-25