Synthesis of C2 Chiral Bidentate Diamine Ligands Derived from Macrocyclic Troger Base and Its Application to Asymmetric Synthesis

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We have succeeded in developing an efficient synthesis of a macrocyclic Troger base with a polyether tether (Trogarophane) by reacting triethylene glycol bis (p-aminophenyl) ether and formalin in HCl-EtOH solution at 80℃ for 18 h. Since the molecular cavity found to be too small for use as a cyclophane host, we turned to the outer dinitrogen moiety. It was expected that when the endo-methylene group is removed, the resulting diamine will become a promising bidentate ligand and, because the inversion is prohibited by the polyether tether, the C2 chiral properties of Troger base will be preserved. Removal of the endo-methylene bridge was not straightforward, because the ether oxygen made the already electron-rich benzene ring more reactive towards oxidixing agents. On successive treatments with trifluoroacetic anhydride and methanolic sodium carbonate the diNH compound was obtained. Methylation of one or both of the nitrogen atoms was completely controlled by suitable selection of the reaction conditions. The optical resolution of all the compounds was effectively accomplished by use of a chiral column (Chiralcel OJ) with increasing efficiency diNMe<NHNMe<Tr o gerophane<diNH.Although the separation for the diNH compound was really remarkable, for the reasons of wide applicability Tr o gerophane was mainly separated. It is gratifying that rather sparingly soluble racemic Trogerophane becomes very soluble on separation so that considerable amounts can be applied on the column with the use of cosolvent. Determination of the absolute structure of the separated Trogerophane is underway.Since the metal ion complexation was confirmed with several kinds of elements, we are currently examining the right conditions for asymmetric synthesis.