Cyclophanes. II. : Preparation and Conformational Properties of 5,14-Bis(4-bromophenyl)diimidazolo[3^2]metacyclophane and a Higher Homolog

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5,14-Bis(4-bromophenyl)diimidazolo[3^2]metacyclophane (12) and 5,14,29,38-tetrakis(4-bromophenyl)tetraimidazolo[3^4]metacyclophane (13) as a higher homolog were synthesized by the one-pot coupling reaction of 1,3-bis(2-isocyano-2-tosylethyl)benzene (3b) with 1,3-bis(4-bromophenyliminomethyl)benzene (11). At -5℃, the proton nuclear magnetic resonance (^1H-NMR) spectrum of 12 strongly suggests the existence of two fixed conformers, i.e., syn and anti forms, on the NMR time scale.Moreover, on the basis of the variable-temperature (VT)-NMR spectra of 12 at various temperatures between 25℃ and 100℃, the coalescence temperature (T_c) of the methylene proton signals is 80℃ and the energy barrier (ΔG^〓) of the conformational change is determined to be 69.3kJ/mol, which is higher than those of the parent[3^2]metacyclophane (4a) and dioxazolo [3^2]metacyclophane (6a). The conformational rigidity of 12 is attributed to the further substitutions of bulky 4-bromophenyl groups on the imidazole moieties in addition to the annelations of two imidazole rings to the two methylene bridges of the [3^2]metacyclophane ring.
社団法人日本薬学会の論文
1988-06-25