Synthesis and crystal structure of [2 + 2] calixsalens

The synthesis and crystal structure of macrocyclic Schiff bases formed in a short reaction time from (1R,2R)-diammoniumcyclohexane mono-(+)-tartrate were investigated. Microwave irradiation of a mixture of bis-(hydroxyaldehydes) and chiral diamines in the presence of potassium carbonate afforded chiral macrocyclic tetraimines in moderate good yields. The structure of the [2+2] macrocycle was confirmed by both MALDI-TOF analysis and single-crystal XRD. The X-ray crystallographic analysis of the unsolved macrocycle Schiff base grown from a hexane-ethyl acetate solution confirmed the cyclic nature of the structure. The macrocycle stack in an eclipsed manner along the crystallographic a-axis, giving rise to infinite columns with macropores. The results show that the crystal structure of the macrocycles resembles that of calixarene and exhibits columnar staking in the solid state.