Selective Formylation of Azacalixpyridine Macrocycles and Their Transformation to Molecular Semicages

The aromatic electrophilic formylation
reaction of azacalix[2]­arene[2]­pyridine
and azacalix[4]­pyridine were systematically studied. By simply controlling
the ratio of reactants and the reaction temperature, the Vilsmeier–Haack
reaction selectively afforded mono-, di-, and tetra-formylated azacalix[2]­arene[2]­pyridines
and azacalix[4]­pyridines. The preferential and selective functionalization
reactions of macrocycles were discussed in terms of their conformational
structure and conjugation effect between aromatic subunits and bridging
nitrogen atoms. All resulting functionalized azacalix[2]­arene[2]­pyridines
and azacalix[4]­pyridines adopted a 1,3-alternate conformation both
in the crystalline state and in solution. Taking advantage of the
close proximity of aldehyde groups in 1,3-alternate di- and tetra-formylated
azacalixpyridine macrocycles, the McMurry reductive coupling reaction
of carbonyls was accomplished to yield unique semicage molecules.

系统研究了氮杂杯[2]芳烃[2]吡啶（azacalix[2]arene[2]pyridine）与氮杂杯[4]吡啶（azacalix[4]pyridine）的芳香亲电甲酰化反应。通过调控反应物配比与反应温度，维尔斯迈尔-哈克（Vilsmeier–Haack）反应可选择性得到单甲酰化、双甲酰化及四甲酰化的氮杂杯[2]芳烃[2]吡啶与氮杂杯[4]吡啶产物。研究结合大环化合物的构象结构，以及芳香亚单元与桥联氮原子间的共轭效应，对其优先选择性官能化反应规律进行了探讨。所有经官能化改性的氮杂杯[2]芳烃[2]吡啶与氮杂杯[4]吡啶，在晶态与溶液状态下均采取1,3-交替构象。借助1,3-交替构象的双甲酰化与四甲酰化氮杂杯吡啶大环中醛基的紧密空间邻近性，本研究完成了羰基的麦克默里（McMurry）还原偶联反应，得到了独特的半笼状分子。