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＝3.9×10 4 L•mol -1 , K2＝2.4×10 4 L•mol -1 , Ka＝ 9.4×10 8 L 2 •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 1 H 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. Keywords macrocycle; pillar[5]arene dimer; oxacalix[4]arene; fixed conformation; host-guest chemistry 1 引言 大环主体分子的高效构筑历来是驱动超分子化学 蓬勃发展的强劲引擎 [1] . 随着分子机器领域的快速发展, 大环分子设计的结构趋于复杂化, 同时构象的固定也成 为其重要方向之一 [2] . 多环类大环分子由于具有协同效 应 [3] , 为构筑多层次自组装结构提供了很好的发展机会.
