Calix[6]arene Derivatives Selectively Functionalized at Alternate Sites on the Smaller Rim with 2-Phenylpyridine and 2-Fluorenylpyridine Substituents to Provide Deep Cavities

The synthesis is described of calix[6]arene derivatives 4, 9, and 14 functionalized at alternate sites on
the smaller rim with 4‘-(pyrid-2‘ ‘-yl)phenylmethoxy, (6‘-phenylpyrid-3‘-ylmethoxy), and {6‘-[2-(9,9-di-n-hexylfluorenyl)]pyrid-3‘-ylmethoxy} substituents, respectively. They were obtained by 3-fold reactions
of 2-[4-(bromomethyl)phenyl]pyridine (3), 5-(bromomethyl)-2-phenylpyridine (8), and 5-(bromomethyl)-2-(9,9-di-n-hexylfluorenyl)pyridine (13) with the 1,3,5-trimethylether of the t-Bu-calix[6]arene in the
presence of sodium hydride in THF in 56−75% yields. Detailed analysis of the 1H NMR spectra (including
variable-temperature data for 4) has established that 4, 9, and 14 exist predominantly in the C3v cone
conformation with minor Cs isomers also observed. The X-ray crystal structure of 4 reveals two molecules
of similar cone conformation, with all three 4‘-(pyrid-2‘ ‘-yl)phenylmethoxy substituents stretched in the
axial direction. Molecule I has a dimeric capsule structure with (pyrid-2‘ ‘-yl)phenylmethoxy substituents
of one molecule interpenetrating those of its inversion equivalent to form a deep enclosed intermolecular
cavity, which contains a CH2Cl2 guest molecule. Molecule II forms no such pair:  the intramolecular
cavity is filled with solvent molecules.

本研究报道了杯[6]芳烃（calix[6]arene）衍生物4、9和14的合成，三者分别在较小下缘的交替位点上修饰有4'-(吡啶-2''-基)苯甲氧基、(6'-苯基吡啶-3'-基)甲氧基以及{6'-[2-(9,9-二正己基芴基)]吡啶-3'-基}甲氧基取代基。它们通过2-[4-(溴甲基)苯基]吡啶（3）、5-(溴甲基)-2-苯基吡啶（8）以及5-(溴甲基)-2-(9,9-二正己基芴基)吡啶（13）与叔丁基杯[6]芳烃的1,3,5-三甲醚在氢化钠存在下的四氢呋喃（THF）溶剂中发生三取代醚化反应得到，产率为56%~75%。对氢核磁共振（1H NMR）光谱（包括衍生物4的变温测试数据）的详细分析表明，4、9和14主要以C3v对称锥式构象存在，同时可检测到少量Cs对称异构体。衍生物4的X射线单晶衍射结构显示，其存在两个构象相似的锥式构象分子，且三个4'-(吡啶-2''-基)苯甲氧基取代基均沿轴向伸展。分子I形成二聚胶囊结构，其中一个分子的(吡啶-2''-基)苯甲氧基取代基与其反演等效分子的取代基相互穿插，形成一个深邃的分子间封闭空腔，该空腔包埋有二氯甲烷（CH2Cl2）客体分子。分子II则未形成此类二聚体：其分子内空腔被溶剂分子填充。