Multi-macrocyclic hosts with fixed conformations provide important platforms for the construction of complicated mechanically inter-locked structures. In order to synthesize rigid multi-macrocycles, a type of oxacalix[4]arene-bridged pillar[5]arene dimers were further derivatized. Firstly, the four NO₂ groups in pillar[5]arene dimer 1 were reduced under catalytic hydrogenation conditions using Raney Ni as a catalyst to give tetraamino compound 2. Unfortunately, the aromatic amino groups in compound 2 were unstable in the air and hard for next investigation of molecular recognition. Therefore, further derivatization was used to introduce more stable aliphatic amino groups. After multiple optimization attempts, the “1+4” intermediate product 3 was obtained in a high yield of 72% from reaction of compound 2 and ten equivalents of t-butoxycarbonyl (Boc)-β-alanine 5 in the presence of dicyclohexylcarbodiimide (DCC) at room temperature. The N-Boc protection groups were further removed in the presence of trifluoroacetic acid in CH₂Cl₂ to afford target compound 4 with four aliphatic amino groups. The structure of 4 was thoroughly confirmed by nuclear magnetic resonance (NMR), high resolution mass spectrometry (HRMS) and X-ray single crystal analysis. X-ray single crystal analysis indicated that the tricyclic host had a shape of binoculars and the conformation was rigid, which could be slightly tuned by different substituents. With a pillar-calix-pillar structure, the host-guest properties of compound 4 were investigated subsequently. Because of its small cavity, oxacalix[4]arene unit played just a role of framework to make two pillar cavities parallel and appropriate for association with guest molecules. The dimers 4 could associate with 1,4-dicyanobutane and form the complex of 2G⸦4 with strong binding ability. The binding constants (K₁=3.9×10⁴ L•mol^–1, K₂=2.4×10⁴ L•mol^–1, K_a=9.4×10⁸ L²•mol^–2) were determined by ultraviolet and visible (UV-Vis) spectroscopy. The complexation between pillar[5]arene dimer 1 with NO₂ group and G was also investigated for comparison. The ¹H NMR spectrum and UV-vis spectroscopy studies indicated the binding ability for 1 was not as good as that for 4. This investigation provides a new opportunity for fabricating hierarchical supramolecular systems.

Key words: macrocycle, pillar[5]arene dimer, oxacalix[4]arene, fixed conformation, host-guest chemistry