Mixed Macrocycles Derived from 2,6-Diformylpyridine and Opposite Enantiomers of trans-1,2-Diaminocyclopentane and trans-1,2-Diaminocyclohexane

The condensation reaction of 2,6-diformylpyridine with an equimolar mixture of opposite enantiomers of trans-1,2-diaminocyclopentane and trans-1,2-diaminocyclohexane using a dynamic combinatorial chemistry approach has been examined. In nonmetal-templated reactions, depending on reaction conditions, mixed 2 + 1 + 1 macrocyclic imine or bigger mixed 4 + 2 + 2 imine macrocycle are formed selectively. The 2 + 1 + 1 imine used as a precursor in the templated by Cd-II ions produces a library of enlarged chiral mixed imines coordinated with metal cations among which the hexanuclear Cd-II complex of 6 + 3 + 3 imine was isolated and characterized. All macrocyclic imine compounds have been reduced to the corresponding macrocyclic amines, which have been further transformed into their hydrochlorides. Each macrocyclic compound has been obtained as two enantiomers. For imine macrocycles and for the hydrochloride derivatives of macrocyclic amines, their X-ray crystal structures have been determined. In particular, the crystals of protonated 4 + 2 + 2 macrocyclic amine, which contains two types of diastereomeric cations differing in terms of inverted twists of pyridine moieties, and hexanuclear Cd-II complex of 6 + 3 + 3 imine, which gives a deeper insight into the expansion reaction, have been investigated. A heterochiral self-sorting of 2 + 2 and 2 + 1 + 1 macrocyclic imines has been confirmed by a competition reaction of 2,6-diformylpyridine, racemic trans-1,2-diaminocyclopentane, and racemic trans-1,2-diaminocyclohexane and theoretical calculations.