Self-assembly of achiral and chiral macrocyclic ligands: synthesis, protonation constants, conformation and asymmetric catalysis

New 30-membered achiral and chiral polyaza macrocyclic ligands, L1 and L2 were synthesized directly from [3 + 3] condensation of phthalic dicarboxaldehyde with cis- and (1R, 2R)-diaminocyclohexane, respectively. The trimeric macrocyclic structures were confirmed by electrospray ionization mass spectrometry (ESI-MS), H-1 NMR, C-13 NMR spectroscopy and elemental analysis. Potentiometry was used to determine the protonation constants of the ligands. UV-vis spectrophotometric titration was employed to investigate the coordination and conformational properties of the chiral ligand (L2). Direct enantioselective aldol reaction has been successfully performed using 4-nitrobenzaldehyde and acetone in the presence of the chiral macrocycle and its zinc(II) complexes as catalysts.