O-Benzylation of the flexible macrocycle 1 with benzyl bromide in the presence of NaH in THF under reflux afforded a mixture of two conformers of the tri-O-benzylated products, cone-2a and partial-cone-2a in a ratio of 20∶80 in 80% yield. In contrast, O-alkylation of the triol 1 with 2-(chloromethyl)pyridine in the presence of NaH resulted in exclusive formation of cone-2b. Only when the template metal can hold the 2-pyridyl group(s) and the oxide group(s) on the same side of the [3.3.3]metacyclophane ring, is the conformation immobilized in the cone form. The template effect of the sodium cation plays an important role in this benzylation.The two-phase solvent extraction data indicated that tris(2-pyridylmethoxy)[3.3.3]metacyclophanes 2b show strong Ag+ affinity, high Ag+ selectivity being observed for both cone-2b and partial-cone-2b. 1H NMR Titration of cone-2b with AgSO3CF3 clearly demonstrates that a 1∶1 complex is formed with retention of the original symmetry. The pyridine moiety underwent conformational changes upon Ag+ complexation with the original outward orientation of the ring nitrogen changing to an inside orientation toward the cyclophane cavity.
在
四氢呋喃中,在 NaH 存在下,用
溴化苄基对柔性大环 1 进行 O-苄基化反应,可得到两种构象的三 O-苄基化产物混合物,即锥体-2a 和部分锥体-2a,两者的比例为 20∶80,产率为 80%。相反,在 NaH 存在下,用 2-(
氯甲基)
吡啶对三醇 1 进行 O-烷基化反应,只能生成锥-2b。只有当模板
金属能将 2-
吡啶基和氧化物基团固定在[3.3.3]偏环的同一侧时,构象才能固定为锥形。两相溶剂萃取数据表明,三(2-
吡啶基甲氧基)[3.3.3]偏环烷 2b 具有很强的 Ag+ 亲和力,锥-2b 和部分锥-2b 都具有很高的 Ag+ 选择性。锥-2b 与 AgSO3CF3 的 1H NMR 滴定清楚地表明,形成的 1∶1 复合物保留了原来的对称性。与 Ag+ 复合后,
吡啶分子的构象发生了变化,环氮原来的外向型变成了环烷空腔的内向型。