1989 Volume 37 Issue 5 Pages 1176-1178
Two novel heterocyclophanes, dioxazolo[32](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°C could be assigned as a syn form, and the energy barrier (ΔG〓) for the conformational flipping at the coalescence temperature (Tc=12°C) was determined to be 58.0 kJ/mol, which is lower than that of dioxazolo[32]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.
