Chiral macrocyclic aliphatic oligoimines derived from trans-1,2-diaminocyclohexane.

Aliphatic dialdehydes of rigid structures having a cyclohexane, a bicyclo[2.2.2]octane or a [7]triangulane skeleton, have been condensed with enantiomerically pure trans-1,2-diaminocyclohexane to give [3+3] or [2+2] macrocyclization products. Unlike acyclic aliphatic imines, these macrocyclic oligoimines show enhanced stabilities and their structures in the crystals could be determined by X-ray diffraction analyses. The enantiomerically pure [7]triangulane dialdehyde showed remarkable diastereoselectivity in the condensation with the two enantiomers of trans-1,2-diaminocyclohexane: only one of the enantiomers gave a [2+2] macrocyclization product. Circular dichroism measurements combined with computational analysis show that the lowest energy electronic transition in these cyclic oligoimines is of n-pi* type.