Dipartimento di Chimica e Biologia "A. Zambelli", Università di Salerno , Via Giovanni Paolo II 132, I-84084 Fisciano, Salerno, Italy.
J Org Chem. 2017 Sep 1;82(17):8973-8983. doi: 10.1021/acs.joc.7b01388. Epub 2017 Aug 21.
The threading of monostoppered alkylbenzylammonium axles 7 and 8 with the calix[6]-wheel 3 can occur by both routes of entering the macrocycle 3 in the cone conformation: passage through the upper rim and the through the lower rim. Thus, under thermodynamic conditions, with both the axles 7 and 8, the two possible orientations of calix[2]pseudorotaxane, namely, endo-benzyl and endo-alkyl, are formed by a stereoselectivity controlled by the endo-alkyl rule. Interestingly, by H NMR monitoring of the threading process between 8 and 3, we revealed two calix[2]pseudorotaxane isomers in which the calix-wheel adopts 1,2,3-alternate and cone conformations, which represent the kinetic and thermodynamic species, respectively. Finally, the synthesis of ammonium-based oriented calix[2]rotaxane is here described.
单帽烷基苄基铵轴 7 和 8 与杯[6]-轮 3 的穿线可以通过进入大环 3 的两种锥体构象的途径发生：穿过上边缘和穿过下边缘。因此，在热力学条件下，对于两个轴 7 和 8，杯[2]假轮烷的两种可能取向，即苄基内型和烷基内型，是由内烷基规则控制的立体选择性形成的。有趣的是，通过对 8 和 3 之间的穿线过程的 1 H NMR 监测，我们揭示了两种杯[2]假轮烷异构体，其中杯轮采用 1,2,3-交替和锥体构象，分别代表动力学和热力学物种。最后，描述了基于铵的定向杯[2]轮烷的合成。
